Part III - Defining Prohibited Force

7 Anomalous Examples of ‘Use of Force’ and Non-‘Use of Force’ under Article 2(4) of the UN Charter

Introduction

The conclusions drawn in Part II regarding the meaning and elements of a ‘use of force’ under article 2(4) of the UN Charter are supported by the principles of treaty interpretation. But there is an interesting and important problem: there are several well-known and accepted ‘uses of force’ that violate the prohibition in article 2(4) but do not conform to all of the criteria set out above. Conversely, there are also some acts that do use physical means or have physical effects but are still not regarded as violating article 2(4). This chapter will set out some of these anomalous examples and then put forward some possible explanations and the implications for the interpretation of a prohibited ‘use of force’ under article 2(4).

Anomalous Examples of ‘Use of Force’

Subsequent Agreements Regarding Anomalous Categories of ‘Use of Force’: The 1974 Definition of Aggression

It is instructive to examine anomalous acts which States agree fall within the scope of article 2(4). For this purpose, the 1974 Definition of Aggression serves as a key example.¹ As explained in Chapter 5, the 1974 Definition is a subsequent agreement on the interpretation of the prohibition of the use of force in article 2(4) of the UN Charter under article 31(3)(a) of the Vienna Convention on the Law of Treaties (VCLT). Some of the acts of aggression (and therefore ‘uses of force’) referred to in the 1974 Definition of Aggression are not strictly ‘armed’ or kinetic forms of force. Article 2 of the 1974 Definition of Aggression provides that:

The first use of armed force by a State in contravention of the Charter shall constitute prima facie evidence of an act of aggression although the Security Council may, in conformity with the Charter, conclude that a determination that an act of aggression has been committed would not be justified in the light of other relevant circumstances, including the fact that the acts concerned or their consequences are not of sufficient gravity.

Article 3 lists acts which may qualify as acts of aggression and is set out and discussed later in the chapter. It provides that: ‘Any of the following acts, regardless of a declaration of war, shall, subject to and in accordance with the provisions of article 2, qualify as an act of aggression’. Article 4 notes that ‘[t]he acts enumerated [in article 3] are not exhaustive and the Security Council may determine that other acts constitute aggression under the provisions of the Charter’. Since articles 1 and 2 of the Definition refer to ‘armed force’, the acts listed in article 3 must all only relate to armed force. As some of the listed acts do not conform to a normal understanding of ‘force’ and do not exhibit all the elements identified in the preceding chapters, it is helpful to examine those acts to assist in the interpretation of the term ‘use of force’ in article 2(4) of the UN Charter. The relevant acts that will be analysed are invasion and military occupation (article 3(a)), blockade (article 3(c)), mere presence in violation of a Status of Forces Agreement (SOFA) (article 3(e)) and indirect use of force either through inter-State assistance (article 3(f)) or through non-State armed groups (article 3(g)).

Article 3(a) The invasion or attack by the armed forces of a State of the territory of another State, or any military occupation, however temporary, resulting from such invasion or attack, or any annexation by the use of force of the territory of another State or part thereof

Ian Brownlie has noted that ‘[i]nvasion and unopposed military occupation following a threat of force, as in the case of the German occupations of the Czechoslovakian territories Bohemia and Moravia in March 1939, are usually regarded as a case of actual resort to force.’² However, the inclusion of military occupation in itself (as opposed to the preceding invasion or attack) as an act of aggression in the 1974 Definition (and therefore an illegal use of force under article 2(4) of the UN Charter) is anomalous because occupation may follow from either a lawful or an unlawful use of force and is not unlawful in itself under the jus contra bellum. Article 42 of the 1907 Hague Regulations defines a territory as occupied ‘when it is actually placed under the authority of the hostile army. The occupation extends only to the territory where such authority has been established and can be exercised’.³ The lawfulness of an occupation is determined under the jus contra bellum, but once it is factually in place then an occupation is regulated by the laws of occupation, including the 1907 Hague Regulations,⁴ the Fourth Geneva Convention 1949⁵ and customary international humanitarian law.⁶ As with an unresisted invasion, an occupation may also meet with no armed resistance and may therefore involve no physical means or physical effects in terms of damage to persons or property.

In the Armed Activities case, the International Court of Justice (ICJ) held that the illegal occupation of Ituri by Uganda constituted a violation of the principle of the non-use of force.⁷ However, this characterisation of the occupation of Ituri was criticised by Judge Pieter Kooijmans since it undermines the separation of the jus contra bellum (which prohibits aggression) and the jus in bello (which sets out the regime governing military occupation and makes no distinction ‘between an occupation resulting from a lawful use of force and one which is the result of aggression’).⁸ Judge Kooijmans argued that article 3(a) of the 1974 Definition of Aggression ‘lent credibility’ to the impression of Governments that ‘“occupation” has become almost synonymous with aggression and oppression’, and held: ‘[t]his resolution, as important as it may be from a legal point of view, does not in all its terms reflect customary law. The reference to military occupation as an act of aggression is in my opinion less than felicitous.’⁹ As Bengt Broms has stated: ‘it could be argued in view of the way in which the paragraph has been construed that the military occupation or the annexation presupposes the existence of an act of aggression in the form of an invasion or attack and that it would therefore not have been necessary to include them separately in this paragraph.’¹⁰ The inclusion in article 3(a) of military occupation as an act of aggression (and therefore a ‘use of force’) is therefore controversial. Nevertheless, since it is a listed act in the 1974 Definition of Aggression, it may be considered that States have made a subsequent agreement under article 31(3)(a) of the VCLT that it is a ‘use of force’ in a violation of article 2(4) of the UN Charter.

Article 3(c) The blockade of the ports or coasts of a State by the armed forces of another State;

A blockade is

a belligerent operation to prevent vessels and/or aircraft of all nations, enemy and neutral, from entering or exiting specified ports, airports, or coastal areas belonging to, occupied by, or under the control of an enemy nation. The purpose of establishing a blockade is to deny the enemy the use of enemy and neutral vessels or aircraft to transport personnel and goods to or from enemy territory.¹¹

For a blockade to be binding under treaty and customary international law, it must meet certain requirements, including that it be effective¹² and ‘applied impartially to the vessels and aircraft of all States’.¹³ A blockade is an anomalous example of an illegal use of force because until it is challenged and enforced, there is a lack of employment of physical means or physical effects – only an expressed intention to use force under certain circumstances (when the blockade is challenged). According to Brownlie, ‘a naval blockade involves an unlawful use of force, although the tactical posture is passive, since its actual enforcement includes the use of force against vessels of the coastal state’.¹⁴

Article 3(c) of the 1974 Definition of Aggression does not specify that a blockade must actually be enforced in order to qualify as an act of aggression. An unchallenged blockade could be considered an act of aggression and therefore a ‘use of force’ because it is an act of warfare that confers a military advantage and is usually employed in conjunction with other forms of force as part of a broader military operation against the armed forces of the blockaded State.¹⁵ However, as with the example to be discussed later of overstaying a Status of Forces agreement, it is not clear if a blockade that is unchallenged may really amount to a ‘use of force’ under article 2(4) of the UN Charter.¹⁶ Nevertheless, an unchallenged blockade constitutes a ‘threat of force’ against the blockaded State and may therefore still violate article 2(4) of the UN Charter.

If a neutral warship or military aircraft attempts to or does breach a blockade, the neutral State commits a violation of the law of neutrality, but the blockading State does not have a right to attack it unless in the exercise of the right of self-defence.¹⁷ But a more interesting legal issue is raised when it comes to the enforcement of a blockade against a neutral merchant vessel on the high seas. Under the jus contra bellum, the enforcement of a blockade against a ship flagged to a neutral State may amount to a use of force within the meaning of article 2(4) and violate the prohibition of the use of force unless justified by one of the recognised exceptions, that is, self-defence. This view is supported by State practice, for example, the position taken by the UK during the Gulf War, when it claimed that Iran’s visit of a British-flagged merchant vessel on the high seas was justified as a measure of self-defence under article 51 of the UN Charter.¹⁸ This implies the legal view that stopping and searching a foreign-flagged merchant vessel on the high seas would otherwise constitute an unlawful use of force in violation of article 2(4) of the UN Charter – that is, that it would not be justified by the law of neutrality.¹⁹ It is not the blockade itself that transforms the capture or attack of the neutral ship into a use of force – due to the principle of exclusive flag State jurisdiction, such interference with a vessel flagged to a third State on the high seas takes place in ‘international relations’ and is arguably itself a use of force unless the capturing/attacking State has lawful grounds for the exercise of jurisdiction over the vessel, for example, under article 110 of the UN Convention on the Law of the Sea.²⁰

But under the laws of naval warfare (jus in bello), ‘since neutral merchant vessels and civilian aircraft are obliged to respect a blockade that conforms to the legal requirements of publicity and effectiveness they become liable to interception and capture if they act in violation of the legitimate right of the blockading power to prevent egress from, or ingress to, the blockaded area’.²¹ Under the jus in bello, neutral merchant vessels and civilian aircraft are liable to be attacked if they are clearly resisting interception and capture, because such an act leads to loss of civilian status and renders the vessel or aircraft a legitimate military objective.²² However, these rules apply under the laws of neutrality and armed conflict, not under the jus contra bellum. The law of blockade and jus in bello do not prohibit the attack, but neither do they justify it under the jus contra bellum. Therefore, attacking a merchant vessel attempting to resist intercept and capture by the blockading State in these circumstances would be an unlawful use of force unless justified by self-defence.

This raises the question of whether the law of neutrality and these rights of blockade continue to apply in the post-Charter era in the traditional way of providing a full justification for certain forcible action. On one view, belligerent rights and the traditional law of neutrality continue to exist in the post-Charter era, which means that the impairment of the rights of third States must be accepted.²³ On another view, the law of neutrality was abolished by the UN Charter and either belligerent rights no longer exist, or they have continued in a modified form under the rubric of self-defence.²⁴ As Stephen Neff notes, there are serious difficulties with each position,²⁵ and this controversial question remains open. Even if one takes the position that these belligerent rights continue to exist but have been modified by the modern jus contra bellum, a further question would be raised of whether the very imposition of a blockade remains a lawful instrument even for a State acting in self-defence, since the principle of effectiveness requires that the blockading State enforce the blockade against neutral vessels resisting interception and capture – in other words, that the blockading State use force against the vessels of third States.²⁶

Article 3(e) The use of armed forces of one State which are within the territory of another State with the agreement of the receiving State, in contravention of the conditions provided for in the agreement or any extension of their presence in such territory beyond the termination of the agreement;

This is an anomalous example of a ‘use of force’ because mere continuing presence of the armed forces of one State within the territory of another State in contravention of a Status of Forces Agreement, even without the actual employment of physical means or the producing of physical effects, may suffice under article 3(e) of the 1974 Definition of Aggression to constitute an act of aggression (and therefore a ‘use of force’ in violation of article 2(4) of the UN Charter), although this is a controversial proposition. Thomas Bruha observes that:

The mere continuance of the presence of armed forces in the territory of another state in violation of, or after the termination of the agreement concluded with it, does not necessarily entail the use of armed force in the ordinary sense of the word. … even if one considers the continued stationing of armed forces ‘within’ another state as a special case of non–transfrontier use of armed force comparable to occupation, it leaves many questions open: what degree of violation of the agreement is required? Must the continued presence of the armed forces in the host state be enforced with threats or other manifestations of the use of armed force?²⁷

The ICJ dealt with this point in the Armed Activities case. In that case, the Court found that Uganda’s actions were not justified by consent or self-defence and that they were a violation of the prohibition of the use of force. The Court acknowledged the Democratic Republic of the Congo (DRC) had previously consented to the presence of Ugandan troops on its territory for a limited purpose of responding to cross-border attacks but that the DRC had a right to unilaterally withdraw this consent without any formalities required.²⁸ The Court found that the DRC had at least by 8 August 1998 withdrawn its consent to the presence of Ugandan troops on its territory.²⁹ The Lusaka Agreement provided for the withdrawal of Ugandan troops from the DRC within a particular timeframe, but the Court found that this did not constitute consent by the DRC to the presence of the Ugandan troops during the withdrawal period³⁰ and that such presence could only be justified, if at all, on the basis of self-defence.³¹ A more recent example is provided by Bruha with respect to

[t]he involvement of units of the Russian Black Sea forces stationed in the Ukraine harbour of Sevastopol in the interventionist activities of Russia leading to the illegal annexation of the Crimea … even if no use of armed force was involved, these activities may be considered as aggression according to article 3(e) of the Definition, because they were instrumental to and occurred in the context of aggressive activities of Russia against Ukraine.³²

Article 3(f) The action of a State in allowing its territory, which it has placed at the disposal of another State, to be used by that other State for perpetrating an act of aggression against a third State;

This ‘use of force’ is also characterised by its lack of physical means or direct physical effects, unless one considers purely indirect means. This form of act of aggression is distinct from the other acts in that it appears to be either a new form of attribution or a broad understanding of the concept of ‘force’.³³ This is because the conduct referred to in article 3(f) is more ‘properly characterised as aid or assistance in the commission of an unlawful use of force by another State within the meaning of Article 16 of the International Law Commission (ILC) Articles on State Responsibility and customary international law’.³⁴ The analysis of article 3(f) by Claus Kreß³⁵ observes that paragraph 8 of the ILC commentary is ambiguous on this point because it characterises the conduct of the assisting State firstly as a breach of the obligation not to use force but in the same paragraph also discusses the Federal Republic of Germany’s acceptance ‘that the act of a State in placing its own territory at the disposal of another State in order to facilitate the commission of an unlawful use of force by that other State was itself an internationally wrongful act’. Kreß observes that:

While the first formulation suggests that the ILC believes that the state conduct described in littera (f) constitutes as such a use of force, the second rather suggests that the ILC characterises such aid and assistance in the commission of an unlawful use of force by another state as an internationally wrongful act related to but distinguishable from a use of force. In any event, the ILC has emphasised that ‘the assisting State is responsible for its own act in deliberately assisting another State to breach an international obligation by which they are both bound’ and that ‘it is not responsible, as such, for the act of the assisted State’.³⁶

If the internationally wrongful act of the assisting State is not a result of the attribution of the act of aggression of the acting State to it but is an unlawful act in its own right, then because of the wording of the 1974 Definition the conduct described in article 3(f) must be considered a ‘use of force’ even though it does not conform to a normal understanding of this term.

This unique form of a prohibited ‘use of force’ requires that the assisting State place its territory at the disposal of another State, that the other State use the territory to perpetrate an act of aggression and that the assisting State ‘allowed’ the use of its territory for this purpose. In terms of the acting State ‘making use of’ the territory of the assisting State for perpetrating an act of aggression, Kreß notes that this occurs ‘if its armed forces or the weapons that are used in the act of aggression are located on that territory’ but that article 3(f) does not require a direct territorial connection with the act of aggression.³⁷ Examples of use of territory falling within the scope of article 3(f) would thus include ‘a command-and-control facility through which the act of aggression is being directed, or a military base from which targeting information for use in the course of the act of aggression is provided’.³⁸ The required degree of involvement of the aggressor (assisting) State within the meaning of article 3(f) requires something approaching ‘active collusion’ rather than ‘mere acquiescence’ or a failure to prevent the use of its territory for perpetrating an act of aggression.³⁹ This degree of involvement therefore requires that the assisting State foresee the misuse of its territory and have ‘knowledge of the circumstances’ of the acts concerned⁴⁰ but does not require that the assisting State place its territory at the disposal of the acting State with the intention that the acting State use it for the purpose of carrying out an act of aggression.⁴¹

An example of inter-State assistance in which article 51 was invoked is Germany’s assistance to the coalition’s use of force in Syria and Iraq in 2015. The German parliament approved the military measures against IS in Iraq and Syria on the basis of article 51 of the UN Charter, article 42(7) of Treaty of the European Union and Security Council Resolutions 2170 (2014), 2199 (2015) and 2249 (2015).⁴² Germany notified the UN Security Council under article 51 of the UN Charter that it had ‘initiated military measures against the terrorist organization Islamic State in Iraq and the Levant (ISIL)’ ‘in the exercise of the right of collective self-defence’, and that ‘[e]xercising the right of collective self-defence, Germany will now support the military measures of those States that have been subjected to attacks by ISIL’.⁴³ Germany’s invocation of article 51 could be evidence of a belief that the acts being justified would otherwise violate article 2(4), namely, support of coalition forces through the provision of intelligence, aerial refuelling and weapons delivery to coalition States. But the legal reasons for invoking article 51 were not explained and despite article 3(f) of the 1974 Definition of Aggression, there is a lack of clear subsequent practice of the parties to the UN Charter demonstrating their agreement that the term ‘use of force’ in article 2(4) includes such forms of inter-State assistance.

Article 3(g) The sending by or on behalf of a State of armed bands, groups, irregulars or mercenaries, which carry out acts of armed force against another State of such gravity as to amount to the acts listed above, or its substantial involvement therein

Similar to article 3(f), article 3(g) of the 1974 Definition of Aggression relates to forms of indirect aggression in which a State facilitates the unlawful use of force by another actor, in this case, by non-State actors. According to the ICJ in the Nicaragua case, the description in article 3(g) applies to the concept of ‘armed attack’ and is customary international law.⁴⁴

There is debate about whether the State’s ‘substantial involvement’ must relate to ‘sending’ or to the acts of armed force of the armed bands.⁴⁵ Kreß points out that the French version is unambiguous that substantial involvement refers to substantial involvement in the sending:

L’envoi par un Etat ou en son nom des bandes ou de groupes armés, de forces irrégulières ou de mercenaires qui se livrent à des actes de force armée contre un autre Etat d’une gravité tel qu’ils équivalent aux actes énumérés ci-dessus, ou le fait de s’engager d’une manière substantielle dans une telle action.⁴⁶

There is also some debate about whether ‘substantial involvement’ is an alternative to or an application of the attribution test (direction or control); in other words, whether the conduct described is a form of ‘indirect force’ by the State itself or a form of attribution of the use of force by the armed group to the State. Article 3(g) of the 1974 Definition of Aggression must be read together with the chapeau of article 3 and article 2 of the Definition of Aggression, which refers to the first use of force by a State. Later ICJ judgments also discuss article 3(g) in terms of attribution.⁴⁷ Dapo Akande and Antonios Tzanakopolous⁴⁸ argue that article 3(g) reflects a customary rule for the attribution of acts by non-State actors to a State. Their position is that article 3(g) is merely an application of the direction or control test and that this is how the ICJ has interpreted it in Nicaragua and in the Armed Activities case.

Kreß argues that the test of attribution as set out in article 8 of the ILC Draft Articles should be applied to interpret the term ‘sending’, which according to the ICJ ‘requires effective control over the specific acts in question, which is a very demanding threshold’.⁴⁹ But he goes on to discuss the ‘alternative of the substantial involvement of a state in the sending’, suggesting that this ‘should, at the present stage of the legal development at least, be confined to the exercise of overall control by the aggressor state over the persons concerned, within the meaning of the case law of the international criminal courts, as initiated by the International Criminal Tribunal for the former Yugoslavia’ in the Tadic case.⁵⁰ Kreß’s argument is that it is controversial whether the overall control test of attribution forms part of customary international law (the ICJ has held that it does not). If we follow the ICJ, then ‘the substantial involvement-limb of article 3(g) of the Annex to 1974 GA Resolution 3314 should perhaps best be considered as the articulation of a lex specialis on attribution in the legal context of the prohibition of the use of force’, especially considering that the ICJ has not elaborated on the meaning of ‘substantial involvement in the sending’.⁵¹ But if one adopts this interpretation, the result is that the ‘substantial involvement’ alternative in article 3(g) is rendered ‘entirely redundant’.⁵²

Kreß acknowledges that ‘[t]he ordinary meaning of “substantial involvement” is even wide enough to cover, beyond the exercise of overall control by a state over violent non-state actors, the (mere) toleration by a state of acts of armed force carried out by non-state actors from the territory of that state against another state’.⁵³ But he argues against this broad interpretation since the negotiations on the 1974 resolution do not show consensus on this point, the ICJ has not adopted this interpretation and since the lack of general acceptance of the US attempt to establish a ‘harbouring doctrine’ after the 9/11 terror attacks does not support a new customary international law rule on attribution.⁵⁴ Other scholars, such as Raphaël van Steenberghe interpret the ICJ case law and article 3(g) of the 1974 Definition differently and address the issue in terms of State ‘substantial involvement’ as an alternative to attribution.⁵⁵

In the end, the interpretation of the term ‘substantial involvement’ in article 3(g) affects the scope of article 2(4) (as well as article 51). If one accepts that ‘substantial involvement’ is an alternative to the standard attribution test, the scope of articles 2(4) and 51 may be slightly broader and cover more State forms of involvement in attacks by non-State armed groups. In any case, this unlawful use of force is anomalous because, like the other form of indirect use of force under article 3(f) of the 1974 Definition, it is characterised by its lack of physical means or direct physical effects, unless one considers purely indirect means.

Conclusion

Although articles 1 and 2 of the 1974 Definition refer to ‘armed force’, the acts in article 3 listed earlier do not correspond to a normal understanding of ‘force’. This shows that UN Member States interpret the concept of ‘force’ to include particular acts which do not correspond with the general definition of this term because they lack physical means and/or (direct) physical effects. Some explanations for this are considered at the end of this chapter.

Lower Gravity Anomalous Examples of ‘Use of Force’

In addition to the acts set out in the 1974 Definition, there are other anomalous examples of acts characterised by States as a prohibited ‘use of force’ despite a lack of certain elements such as ‘use’ of physical force or a lack of physical effects. These include the following:

Intentionally Crossing a Border Bearing Arms with an Intention to Use Them Even before Any Weapons Are Fired

The mere crossing of a border by armed forces has sometimes been treated by States as a violation of the prohibition of the use of force, despite a lack of employment of physical means or of physical effects. For example, in the case of the Temple of Preah Vihear, Cambodia argued that Thailand committed a ‘flagrant violation of Article 2, paragraph 4 of the Charter’⁵⁶ when it sent detachments of its armed forces to territory claimed by Cambodia in 1954 but subject to a border dispute between those two States, despite a lack of armed confrontation.⁵⁷ Similarly, in September 1964, Malaysia complained to the UN Security Council that Indonesia had committed ‘blatant and inexcusable aggression’ when it sent heavily armed paratroopers into Malaysian territory in the context of a broader political dispute.⁵⁸ The practice is however not clear-cut. For example, when Israeli commandos assassinated Khalil al-Wazir in Tunis on 16 April 1988, the UN Security Council adopted Resolution 611 (1988) condemning ‘the aggression … against the sovereignty and territorial integrity of Tunisia in flagrant violation of the Charter of the United Nations, international law and norms of conduct’.⁵⁹ However, it is unclear from the international response to this incident whether the mere act of sending Israeli armed forces into Tunisia for the purpose of carrying out the assassination (as opposed to the actual assassination itself) was sufficient in itself to constitute a prohibited ‘use of force’, having regard to the fact that no direct combat took place between the Israeli commando unit and Tunisian armed forces.⁶⁰

Aerial Incursion

Similarly, there have been numerous instances of aerial incursion that States have treated as violations of the prohibition of the use of force, and in some cases, as an armed attack under article 51 of the UN Charter giving rise to a right to self-defence despite the lack of employment of physical force and lack of physical effects. For instance, Iraq, Lebanon and Libya have issued complaints to the UN Security Council regarding recurrent US incursions into their airspace, invoking the right of self-defence.⁶¹ Likewise, the attempted US hostage rescue operation in Tehran on 24 April 1980 was characterised by both the United States (due to its invocation of article 51)⁶² and Iran⁶³ as ‘force’ despite the relatively short period of the incursion and lack of any direct encounter with Iranian forces.⁶⁴ But the practice is mixed, since in similar cases of aerial incursion, article 2(4) or article 51 were not invoked. In the Nicaragua case, unauthorised overflight of territory was treated as a violation of sovereignty and was not characterised as a use of force.⁶⁵

In the Nicaragua case, the ICJ held that ‘[t]he principle of respect for territorial sovereignty is … directly infringed by the unauthorized overflight of a State’s territory by aircraft belonging to or under the control of the government of another State’.⁶⁶ However, the practice surveyed earlier demonstrates that States sometimes treat aerial incursion as an unlawful ‘use of force’ and not only a violation of sovereignty. If one considers that aerial incursion may indeed constitute an unlawful use of force, then the interesting question is raised of why this should be so, even when there is no application of physical force or physical effects. Note that this differs slightly from the issue of the legal regime governing the territorial State’s response to such incursion, which is discussed later in the context of anomalous non-uses of force.

Conclusion

The anomalous examples of ‘use of force’ discussed earlier seem to be characterised by no use of weapon or no physical effects but an interference with sovereignty. The first category involves military incursion without recourse to the use of weapons, for example: unopposed invasion and unopposed military occupation, intentionally crossing a border bearing arms with an intention to use them even before any weapons are actually fired and aerial incursion into sovereign airspace. Other examples involve unconsented mere presence in territory, such as an unchallenged blockade and overstaying a Status of Forces Agreement. Another category of anomalous examples relates to the indirect use of force through assisting another State or non-State armed groups in their use of force.

Anomalous Examples of Non-‘Use of Force’

In addition to the above anomalous accepted instances of ‘use of force’ that do not correspond to the general interpretation of this term, there are also anomalous examples of forcible acts that appear to meet the key criteria of a ‘use of force’ but are nevertheless not characterised as illegal uses of force under article 2(4) of the UN Charter. This part will discuss anomalous examples of non-use of force in the air and at sea.

Forcible Response to Aerial Incursion

The previous analysis discussed State practice regarding aerial incursion into sovereign airspace and its characterisation as a ‘use of force’ in some instances. A related anomaly is the legal characterisation of forcible response to such incursion, such as shooting down the aircraft, as not a ‘use of force’ and therefore falling outside the scope of the jus contra bellum. For instance, in 1983, the Korean aircraft KAL flight 007 was mistaken for a spy plane and shot down by fighters in Soviet airspace. This was widely condemned but article 2(4) was not invoked; instead, the shooting down of the aircraft was condemned as inhumane and disproportionate and in violation of Annex 2 of the Chicago Convention on International Civil Aviation (‘Chicago Convention’) regarding interception of civilian aircraft.⁶⁷ In 1996, the Cuban Air Force shooting down two civil aircraft was widely condemned as a violation of article 3bis of the Chicago Convention and resulted in UN Security Council Resolution 1067 (1996) condemning it without mentioning article 2(4) of the UN Charter.⁶⁸

Scholars are divided over the question of whether the use of force by a State against intruding military aircraft in its own territory is governed by the jus contra bellum, or law enforcement/air law.⁶⁹ For example, Olivier Corten argues that the shooting down of a single military aircraft intruding in airspace is governed by air law rather than the jus contra bellum: ‘if the measures taken against an intruding aircraft are considered police measures for air security, we are referred on to other conditions of lawfulness: prior warning, unless there is a manifest hostile intent, necessary and proportionate measure, or riposte in self-defence’.⁷⁰ In Corten’s view, air law and the jus contra bellum have ‘two separate domains of application’.⁷¹ In support of this view, he cites articles 1 and 3bis(a) of the Chicago Convention (the latter which however states that ‘[t]his provision shall not be interpreted as modifying in any way the rights and obligations of States set forth in the Charter of the United Nations’). Corten also notes the International Law Commission’s discussion of circumstances precluding wrongfulness uses the example of an aircraft in distress entering airspace unauthorised as being justified as force majeure or distress. Since the ILC regards article 2(4) as a peremptory norm, this aircraft example must not fall under the jus contra bellum but under aviation rules since violations of jus cogens cannot be justified by circumstances precluding wrongfulness and lex specialis is not applicable to such norms.⁷² According to Corten, the way to determine which body of rules is applicable depends ‘on the type of action in question, whether a simple police measure in the first instance, or an act of force in international relations in the second’.⁷³

In contrast to Corten, Tom Ruys argues:

One cannot rely on the argument that ‘minimal’ use of armed force by way of enforcement measures within a state’s own territory would somehow find its legal basis in ‘particular (and mainly conventional) legal regimes on land (such as the Schengen convention), at sea (such as the Montego Bay convention), or in the air (such as the Chicago convention).’ None of the conventions cited provides a legal basis for forcible action against unlawful territorial incursions by military or police forces of another state.⁷⁴

He concludes that: ‘whenever state A deliberately uses (potentially) lethal force within its own territory – including its territorial sea and its airspace – against military or police units of state B acting in their official capacity, that action by state A amounts to the interstate use of force in the sense of UN Charter Article 2(4).’⁷⁵

A more recent incident raising this issue concerned the shooting down of a Russian fighter jet by Turkey on 24 November 2015. The jet was in the region as part of Russia’s ongoing operation in Syria fighting the opposition with the consent of the Assad government. Russia disputes that its jet crossed the Turkish border, but Turkey claimed that:

2 SU-24 planes, the nationality of which are unknown have approached Turkish national airspace in Yayladaga/Hatay region. The planes in question have been warned 10 times during a period of 5 minutes via ‘Emergency’ channel and asked to change their headings south immediately. Disregarding these warnings, both planes, at an altitude of 19.000 feet, violated Turkish national airspace to a depth of 1,36 miles and 1,15 miles in length for 17 seconds from 9.24′.05″ local time. Following the violation, plane 1 left Turkish national airspace. Plane 2 was fired at while in Turkish national airspace by Turkish F-16s performing air combat patrolling in that area in accordance with the rules of engagement. Plane 2 crashed onto the Syrian side of the Turkish-Syrian border.⁷⁶

Russia strongly protested against the shooting down of its jet and claimed that at the time it was shot down, it was 4 km within Syrian territory. It is clear that if Russia’s aerial incursion was an armed attack, Turkey would have the right to use force in self-defence under article 51 of the UN Charter. Under the jus contra bellum, Turkey’s response would be governed by the conditions of necessity and proportionality.⁷⁷ If it is proportionate to the goal of halting the attack,⁷⁸ then the plane may be shot down. The key issue would then be when the right to self-defence arises – that is, when an ‘armed attack’ ‘occurs’. There are different views regarding when the right to self-defence arises: for example, ‘interceptive self-defence’⁷⁹ or imminence.⁸⁰ But if such an aerial incursion does not constitute an armed attack, then there is difficulty with explaining the legal basis for response to those small-scale incidents due to the ‘gap’ between a prohibited ‘use of force’ under article 2(4) and the higher gravity threshold of an ‘armed attack’ under article 51.

It remains disputed whether there is a right to use force against intruding military aircraft unless in self-defence.⁸¹ But since it is very restrictive to hold that States can only respond to aerial incursions by military aircraft within their territory with force in the event of a strictly construed armed attack, there are three legal possibilities to address this. Firstly, one can interpret a lower threshold for ‘armed attack’ giving rise to a right of self-defence. Secondly, one can find an exception to the prohibition of the use of force outside article 51 self-defence and Chapter VII enforcement action – for example, ‘proportionate defensive action against incipient attack’,⁸² or forcible countermeasures by the victim State to acts violating article 2(4) but falling short of article 51 armed attack⁸³ (however, this view is firmly in the minority position since it is widely accepted that since the advent of the UN Charter, forcible countermeasures, that is armed reprisals,⁸⁴ are unlawful).⁸⁵ The third possibility – which would constitute an anomalous example of non-use of force – is to interpret the prohibition of the use of force as not applying to a State’s use of force against incursions by the military of another State within its own territory. This could either be on the basis that the contextual requirements of article 2(4) are not met, since the forcible act is not ‘in international relations’ or against the territorial integrity or sovereignty of another State or against the purposes of the United Nations, or on the basis that the act does not constitute a ‘use of force’.

Maritime Law Enforcement against Foreign-Flagged Vessels with No Basis for Jurisdiction

A further example of forcible acts that appear to meet the criteria for a ‘use of force’ but are not consistently characterised as such relates to maritime law enforcement against foreign-flagged vessels that is without lawful basis. The use of force at sea is a complex issue, because it is governed by a parallel legal regime: the law of the sea. The law of the sea as embodied in the UN Convention on the Law of the Sea (UNCLOS)⁸⁶ recognises different legal spaces at sea and strikes a balance between the rights of coastal States and the general interest of all States to freedom of navigation and peaceful uses of the sea. The resulting regime can result in multiple States having enforcement jurisdiction over the same physical space because of the principle of exclusive flag State jurisdiction, territorial sovereignty of the coastal State over internal waters and the territorial sea (with the territorial sea subject to certain rights of other States such as innocent passage), a customs and immigration enforcement area within the contiguous zone but outside territorial waters, and the exclusive economic rights of the coastal State within its Exclusive Economic Zone (subject to freedoms of the high seas such as navigation, overflight and laying of cables). This is the most fraught zone of the seas, because it is here that there is a complex balance between the rights of the coastal State and the rights of all other States; this is a result of a compromise to create a new zone, the Exclusive Economic Zone of 200 nautical miles, while preserving other rights of third States. Not all rights are assigned within this area, so there remains uncertainty over the legal rights that the coastal State and other States are entitled to exercise within this zone. UNCLOS also recognises other maritime spaces such as transit straits, archipelagic seas and the high seas (subject to freedom of navigation and peaceful uses).⁸⁷

In respect of purported maritime law enforcement with no basis for jurisdiction, despite the presence of elements of a ‘use of force’ identified in Part II, States do not always characterise such acts as a violation of article 2(4) of the UN Charter. The following section will discuss two examples of anomalous non-uses of force: response to non-innocent passage through the territorial sea by submerged submarines and unlawful attempts to exercise law enforcement jurisdiction on the high seas against foreign vessels (which has no legal basis outside certain recognised exceptions under customary international law and treaty, e.g. article 110 of UNCLOS).

An anomalous example of forcible acts which are not usually characterised as an unlawful ‘use of force’ is the forcible response to non-innocent passage of submerged submarines through the territorial waters of another State. The coastal State has sovereignty over the territorial sea, which may extend twelve nautical miles from the baseline.⁸⁸ Foreign vessels, including warships and submarines, have a right of innocent passage through the territorial sea.⁸⁹ According to article 19(1) of UNCLOS, ‘[p]assage is innocent so long as it is not prejudicial to the peace, good order or security of the coastal State. Such passage shall take place in conformity with this Convention and with other rules of international law’. Article 19(2) of UNCLOS specifies acts which render passage not innocent, including ‘(a): any threat or use of force against the sovereignty, territorial integrity or political independence of the coastal State, or in any other manner in violation of the principles of international law embodied in the Charter of the United Nations’. Article 20 states that: ‘[i]n the territorial sea, submarines and other underwater vehicles are required to navigate on the surface and to show their flag’. Furthermore, according to article 25(1): ‘[t]he coastal State may take the necessary steps in its territorial sea to prevent passage which is not innocent’. Under customary international law, foreign government vessels such as warships and submarines have sovereign immunity from the jurisdiction of any State except their flag State.⁹⁰ UNCLOS is silent on the measures that may be taken in response to non-innocent passage, and its article 25 does not explicitly authorise a forcible response to non-innocent passage. Thus, it is unclear which legal regime governs the forcible response of the coastal State to non-innocent passage by foreign government vessels.

This issue comes to the fore in instances of submerged submarines entering the territorial waters of another State in violation of article 20 of UNCLOS. For example, in 1982,

Sweden utilized depth charges and mine detonations in its efforts to force a submarine that was near one of its naval bases to the surface, and further threatened to sink foreign submarines if they refused to surface and leave Sweden’s waters. This threat was generally tolerated by other states, and could thus be indicative of what responses may lawfully be taken to respond to this particular security concern.⁹¹

A similar issue was raised in 2004 when a submerged submarine which was later identified as Chinese entered Japan’s territorial sea. ‘[A] “maritime security operation” (kaijo-keibi-kodo) was ordered to the Commander of the Japan Maritime Self-Defense Force (JMSDF) Fleet, and patrol helicopters and vessels of the JMSDF joined the operation.’⁹² The incident was framed by Japan as a violation of international law (specifically of article 20 of UNCLOS to which Japan and China are party). There was no invocation of the language of article 2(4) or article 51 of the UN Charter. Japan demanded an apology, explanation and assurance of non-repetition. Despite calls in the Japanese Diet for greater clarity over the measures that may be taken against submerged submarines in such situations, the government response plan does not address what measures it believes a State may take in response to violations of article 20.⁹³

These examples are anomalous because a coastal State may not exercise law enforcement jurisdiction over a foreign warship or submarine, since foreign government vessels enjoy sovereign immunity. Thus, a use of force against submerged submarines in the territorial sea in an attempt to bring them to the surface and require them to leave the territorial sea is not authorised by UNCLOS nor customary international law. ‘To the extent that any maritime security threats or breaches are state sponsored, law enforcement powers against sovereign immune vessels are not available. Instead, questions involving the threat or use of force may arise and diplomatic or other avenues for dispute settlement must be pursued.’⁹⁴ In the absence of a basis for the exercise of jurisdiction against such vessels, a use of force against them would appear to be in international relations and fall within the ambit of the prohibition of the use of force under article 2(4) of the UN Charter, so it is curious that States do not always invoke self-defence to respond to submerged submarines in territorial waters. However, omitting to invoke article 2(4) or article 51 does not necessarily indicate an opinio juris that such incidents definitively fall outside the scope of article 2(4), since it could be motivated by other considerations (such as political) and also due to uncertainty over the applicable legal framework.

With respect to attempted law enforcement against foreign-flagged vessels on the high seas, this is sometimes but not always characterised as an unlawful use of force under the jus contra bellum. On the high seas, the principle of mare liberum and exclusive flag State jurisdiction with only few exceptions applies. This was affirmed by the Permanent Court of International Justice in the SS Lotus case: ‘It is certainly true that – apart from certain special cases which are defined by international law – vessels on the high seas are subject to no authority except that of the State whose flag they fly.’⁹⁵ Exceptions to sole flag State jurisdiction on the high seas include the right of hot pursuit, plus ‘the right of visit in relation to piracy, slave trading, drug trafficking, people smuggling, and unauthorized broadcasting’.⁹⁶ Therefore, attempts by a State to exercise jurisdiction against a foreign vessel on the high seas outside of these recognised exceptions or on the basis of a specific treaty (such as the 1995 Fish Stocks Agreement⁹⁷) have no legal basis. With respect to interdiction (unilateral boarding and arrest of a vessel) by the non-flag State on the high seas, Douglas Guilfoyle argues that such unauthorised interference is ‘a clear attack on a State’s sole means of exercising a fundamental right’.⁹⁸

A prominent example of high-gravity employment of force in purported law enforcement on the high seas without lawful basis is the 1967 bombing of a Liberian-flagged oil tanker, Torrey Canyon, by the United Kingdom to prevent marine pollution after it ran aground on the high seas outside British territorial waters.⁹⁹ ‘The operation, conducted by the RAF, lasted several days with napalm bombs being dropped on the wreck to release and burn the oil remaining in the ship’s tanks.’¹⁰⁰ The legal debate following the incident turned around the lawfulness of police measures on the high seas to prevent the risk of pollution, including the possibility of invoking necessity as a ground precluding wrongfulness.¹⁰¹ Although the UK had no grounds for exercising law enforcement jurisdiction over the Liberian-flagged vessel on the high seas, and despite the high gravity of means and physical effects, the incident was not characterised as a ‘use of force’ under article 2(4) of the UN Charter. Corten argues that this precedent confirms that two separate legal frameworks can apply to the use of force at sea: one relating to police measures based on treaty or customary rules of the law of the sea, and the other governed by the jus contra bellum.¹⁰² However, due to the lack of legal grounds for exercising law enforcement jurisdiction in this case, this argument is not convincing and the reasoning may lie elsewhere.¹⁰³

The Fisheries Jurisdiction (Spain v Canada) case¹⁰⁴ before the ICJ is also sometimes cited in support of the argument that there is a de minimis gravity threshold that divides a ‘“minimum use of force”, that can be ascribed to simple police measures, and a more serious use, that might come within the ambit of article 2(4)’.¹⁰⁵ In this case, Canada had entered a reservation to its acceptance of the Court’s compulsory jurisdiction excluding the Court’s jurisdiction over ‘disputes arising out of or concerning conservation and management measures taken by Canada with respect to vessels fishing in the NAFO Regulatory Area, as defined in the Convention on Future Multilateral Co-operation in the Northwest Atlantic Fisheries, 1978, and the enforcement of such measures’. On the same day, Canada introduced domestic legislation regarding conservation and management measures over parts of the high seas. Canada then later enforced that legislation on the high seas 245 miles from the Canadian coast against a Spanish fishing vessel, the Estai, by boarding, inspecting and seizing the vessel. Spain protested and claimed that this was an unlawful use of force in violation of article 2(4). Canada argued that the Court had no jurisdiction to hear the dispute, since it fell within the scope of its reservation. Spain argued that since the acts complained of were unlawful under the UN Charter, they could not be regarded as falling within the scope of the Canadian reservation. Consequently, the case ultimately concerned whether the matter was a ‘dispute[] arising out of or concerning conservation and management measures taken by Canada with respect to vessels fishing in the NAFO Regulatory Area, as defined in the Convention on Future Multilateral Co-operation in the Northwest Atlantic Fisheries, 1978, and the enforcement of such measures’.

The Court found that it had no jurisdiction because the measures taken against the Estai fell within the scope of Canada’s reservation. In particular, it stated:

Boarding, inspection, arrest and minimum use of force for these purposes are all contained within the concept of enforcement of conservation and management measures according to a ‘natural and reasonable’ interpretation of this concept.¹⁰⁶

This statement has been relied upon by Corten to support his position regarding a de minimis gravity threshold distinguishing law enforcement measures from a ‘use of force’ at sea. However, a close reading of the judgment shows that the Court was not drawing a boundary between ‘use of force’ under article 2(4) and the enforcement of conservation and management measures at sea. In fact, the Court explicitly declined to scrutinise the legality of the measures under international law (including article 2(4) of the UN Charter) since it did not have jurisdiction to do so.¹⁰⁷ The Court confined itself to interpreting ‘conservation and management measures’ in a technical sense (to see if the acts fell within the scope of Canada’s reservation from its acceptance of the Court’s jurisdiction) and was careful to distinguish this from the legality of the measures under international law. It was therefore left unsettled whether the enforcement measures violated article 2(4). This case therefore provides no support either in favour or against a gravity threshold that distinguishes law enforcement measures and a ‘use of force’ under article 2(4).

Conclusion

An analysis of anomalous examples of non-‘use of force’ such as forcible response to aerial and maritime incursion and purported maritime law enforcement may further clarify the complex relationship between competing applicable legal frameworks and where the boundaries between them lie, as well as indicate which elements of a ‘use of force’ are necessary and the relationship between those elements. The next section will discuss possible legal explanations for these anomalous ‘uses of force’ and non-‘uses of force’ under article 2(4) of the UN Charter.

Possible Explanations

The problem remains of how to reconcile these seemingly anomalous examples with a coherent definition of a prohibited ‘use of force’ under article 2(4) of the UN Charter. There are several possible explanations for these anomalous examples of ‘use of force’ and non-‘use of force’, namely, that these are agreed exceptions to the general interpretation of a ‘use of force’ under article 2(4), the concept of ‘use of force’ is broader than generally understood or that a ‘use of force’ is characterised not by a checklist of essential elements but of a basket of elements to be weighed and balanced. Each of these interpretive possibilities are canvassed further in the following sections.

1. These Are Agreed Exceptions to the General Interpretation of Article 2(4)

One possibility is that these anomalous examples are merely agreed exceptions to the general interpretation of a ‘use of force’ under article 2(4) and customary international law. This possibility is not excluded but would need to be strongly supported by subsequent agreement or evidence of subsequent practice demonstrating the parties’ agreement to this interpretation. If one considers 1974 GA Resolution 3314 as a subsequent agreement regarding the interpretation of article 2(4) of the UN Charter,¹⁰⁸ an argument could be constructed to support recognised exceptions to the general interpretation of this term, as set out in the preceding section, namely: military occupation (as distinct from the invasion or armed attack preceding it) (article 3(a)), an unenforced blockade (article 3(c)), mere continuing presence in contravention of SOFA (article 3(e)) and indirect aggression either through ‘[t]he action of a State in allowing its territory, which it has placed at the disposal of another State, to be used by that other State for perpetrating an act of aggression against a third State’ (article 3(f)) or ‘[t]he sending by or on behalf of a State of armed bands, groups, irregulars or mercenaries, which carry out acts of armed force against another State of such gravity as to amount to the acts listed above, or its substantial involvement therein’ (article 3(g)). In this case, the general definition of a prohibited ‘use of force’ would apply, requiring the presence of the identified elements of a ‘use of force’, unless an act fell within the scope of an agreed special case.

This is of course possible, but there are two issues with this explanation. The first is that it would be preferable to find a solution that results in a consistent interpretation of this provision. This is not an insurmountable objection, since it may be that this is the situation lex lata even though it may not be the preferred interpretive outcome as a matter of legal policy. The second and more important issue with this explanation is that, although it explains certain anomalous examples of ‘use of force’ that do not display the usual elements (such as physical means or physical effects), it does not fully explain the phenomena in question. For instance, it does not explain anomalous examples of non-use of force discussed earlier (although of course, these could also be subsequent agreements regarding acts that fall outside the scope of the prohibition). It also does not provide a satisfactory definition of an unlawful ‘use of force’ for acts that do not fall within subsequently agreed special exceptions to the general definition. As will be argued in more detail in the following chapter, a prohibited ‘use of force’ (even one that is a ‘standard’ type of force and not a special case such as unresisted invasion) is not characterised by a checklist of essential elements. The theory of subsequently agreed special types of ‘use of force’ therefore does not provide a full explanation of how to identify whether certain acts fall within the general definition.

2. The Interpretation of ‘Use of Force’ Is Broader than Generally Understood

An alternative explanation for these anomalous uses of force and non-uses of force is that the definition of a prohibited ‘use of force’ is broader than previously understood and encompasses acts which do not conform with the typical understanding of ‘force’ as derived in Part II. The 1974 Definition of Aggression could be regarded as a subsequent agreement that shows that UN Member States share a broader understanding of the concept of ‘armed force’. The majority of the acts listed (articles 3(a)–(d)) involve classical acts of inter-State warfare, namely, invasion, military occupation, bombardment, blockade and attacks on the armed forces of a State or its marine and air fleets. The remainder of listed acts involve a special case of violation of sovereignty that could be (at a broad level) considered similar to military occupation due to the unconsented to and thus unlawful presence of the armed forces of another State within a State’s territory (in the case of article 3(e)), and as closing loopholes in unlawful conduct by enclosing forms of indirect aggression such as certain forms of assistance to another State to commit aggression (article 3(f)) or through sending/substantial involvement in the armed attack against a State by a non-State armed group (article 3(g)). All of these acts (including the case of attacks against the marine or air fleets of a State, due to the nexus to the State demanded by the scale of the attack, as denoted by the term ‘fleets’) share in common a violation of the territorial integrity, sovereignty and political independence of the victim State and serve to protect these interests. Therefore, in this sense it could be hypothesised that an unlawful use of force is something broader than the application of violence between States and encompasses any significant injury to the fundamental rights of State sovereignty and political independence.

This is more satisfactory than the previous hypothesis, because it provides a coherent (if presently vague) definition of a ‘use of force’. But it is also problematic because like the first hypothesis, it does not fully explain why some acts fall within or outside the definition. Why is it that these acts should still be considered a ‘use of force’ under article 2(4) despite lacking certain elements, such as physical means or physical effects? Does it mean that those elements are not really necessary for an act to constitute a prohibited ‘use of force’? How is this to be reconciled with the fact that most uses of force do display these elements? And, even more problematically, the possibility under consideration does not explain why other acts which may very well violate the territorial integrity, sovereignty and political independence of the victim State are not characterised as prohibited ‘uses of force’, such as certain forms of support for armed non-State groups. To conclude that the anomalous examples discussed earlier are explained by a broader understanding of ‘use of force’ is also unsatisfactory because it risks giving the prohibition of the use of force an overreach.

3. ‘Use of Force’ as a Type Rather than a Concept

The third and arguably more convincing hypothesis is that these anomalous examples of use of force and non-use of force may be reconciled with a consistent interpretation of ‘use of force’ if it is accepted that a ‘use of force’ under article 2(4) of the UN Charter is a type rather than a concept. In other words, it may be that not all of the elements identified in Part II are necessary, although in particular combinations they may be sufficient, to constitute a ‘use of force’. This hypothesis is explored in more detail in Chapter 8.

8 The Meaning of Prohibited ‘Use of Force’ in International Law

Introduction

This chapter proposes a framework for the definition of a prohibited ‘use of force’ that incorporates the elements identified in Part II and reconciles the anomalous examples of ‘use of force’ and non-‘use of force’ discussed in Chapter 7. It argues that a prohibited ‘use of force’ under article 2(4) of the UN Charter and customary international law is not a single category in which essential elements must all be present in order for an act to fall within the definition but rather that there are different ‘types’ of ‘use of force’ in relation to which these elements may be present in different combinations and must be weighed and balanced to determine if they meet a particular threshold. The theory of ‘type’ is firstly set out before explaining how it applies to the prohibition of the use of force between States in international law, with illustrative examples from State practice and two case studies. These case studies will apply type theory to two very different potential ‘uses of force’: the attempted killing of Sergei Skripal in the UK in 2018 with the nerve agent Novichok, and the use of force in outer space, to demonstrate how to apply type theory in practice to assess whether an act is a prohibited ‘use of force’. Finally, this chapter proposes a general framework to identify an unlawful ‘use of force’ according to this theory.

What Is a Type?

In the sense employed here, type denotes a category (here: ‘use of force’) which contains certain conditions (elements, such as physical means, physical effects etc.), not all of which are necessary or sufficient but which must be weighed and balanced to determine whether the threshold for the definition is met. A type is to be distinguished from a concept, in which an object (e.g. a forcible act) belongs to the set (‘use of force’) only if the shared group of necessary conditions are met (i.e. the conditions are all necessary and are jointly sufficient). A typical example of a concept is the definition of crimes: due to the requirements of nullum crimen sine lege, crimes under domestic and international law are typically defined by elements which must all be met in order for a particular act to fall within the definition. An example for illustrative purposes is the war crime of wilful killing, which has the following elements under article 8(2)(a) of the Rome Statute of the International Criminal Court (Elements of Crimes, footnotes omitted):

Elements

1. 1. The perpetrator killed one or more persons.

2. 2. Such person or persons were protected under one or more of the Geneva Conventions of 1949.

3. 3. The perpetrator was aware of the factual circumstances that established that protected status.

4. 4. The conduct took place in the context of and was associated with an international armed conflict.

5. 5. The perpetrator was aware of factual circumstances that established the existence of an armed conflict.

Under this definition, each of the aforementioned elements is necessary and when these elements are all fulfilled, then they are also jointly sufficient for meeting the definition of the crime.

In contrast, it is proposed that a prohibited ‘use of force’ between States within the meaning of article 2(4) of the UN Charter is defined by a basket of elements, not all of which are necessary conditions; these elements do not all have to be present for an act to meet the definition. Instead, these elements are identified and weighed up to determine whether the threshold of the definition is met. In other words, individually each of these elements may not be necessary, but in a given case a particular combination of them may be jointly sufficient to constitute a prohibited ‘use of force’. Conversely, if none of the elements are present, although they are not individually necessary, then the act will not constitute a prohibited ‘use of force’.

The crime of Nötigung (coercion) under German criminal law provides an instructive illustration of the idea of type. Nötigung is a catch-all provision in section 240 of the German Criminal Code which criminalises the threat or use of force to coerce another person to carry out, suffer or refrain from an act.¹ The crime is defined as follows:

Section 240 of the Strafgesetztbuch (German Criminal Code)²

Using threats or force to cause a person to do, suffer or omit an act

1. (1) Whosoever unlawfully with force or threat of serious harm causes a person to commit, suffer or omit an act shall be liable to imprisonment not exceeding three years or a fine.

2. (2) The act shall be unlawful if the use of force or the threat of harm is deemed inappropriate for the purpose of achieving the desired outcome.

3. (3) The attempt shall be punishable.

4. (4) In especially serious cases the penalty shall be imprisonment from six months to five years. An especially serious case typically occurs if the offender

   1. 1. causes another person to engage in sexual activity;

   2. 2. causes a pregnant woman to terminate the pregnancy; or

   3. 3. abuses his powers or position as a public official.³

The definition of the crime of Nötigung requires that the behaviour be unlawful. This is essentially a means-ends analysis, as set out in sub-section (2). However, it can also be unlawful under this analysis to achieve a lawful outcome with a lawful act if the means (the use of force or the threat of harm) ‘is deemed inappropriate’ for that purpose. For example, this is usually discussed in relation to making threats to lodge a legitimate criminal complaint with the authorities in cases where the desired outcome of the threat (for instance, repaying a debt) is not connected with the criminal complaint itself (i.e. a case of blackmail). Other examples of Nötigung include (a) locking up a person;⁴ (b) preventing a person from entering a building;⁵ (c) ‘unwanted’ anaesthesia;⁶ (d) turning off the heating of a property to compel the tenant to pay the rent;⁷ and (e) tailgating in traffic.⁸

What is interesting about the crime of Nötigung for our purposes is that the German courts have interpreted this crime as comprising a number of factors which must be weighed up and which do not all have to be present for a particular act to be ‘deemed inappropriate’ under section 240(2) and thus fall within the scope of the crime. Under the current definition of ‘use of force’ with respect to Nötigung, two elements of ‘force’ must be present: ‘force’ is defined as any physical action that produces a physical effect on the victim (to break his or her (expected) resistance).⁹ However, the threshold of these requirements is extremely low; the mere act of sitting down or turning a key meets the requirements for a physical action, and a physical reaction (such as perspiring) can suffice to meet the requirements for a physical effect. There is one minor limitation to this, however: force against objects is usually not enough unless it also indirectly impacts on a person (e.g. destroying windows of a building in the winter so that the residents must vacate the premises).

In order to meet the elements of the crime of Nötigung, all relevant factors must be considered, although their specific requirements are debatable, including:

• lawfulness, weight and acceptability of the desired outcome;

• the intensity of the force;

• motivation;

• the weight of the encroachment on the freedom of the recipient of the use of force;

• a greater than insignificant effect on the receiver;

• priority of public authority (i.e. no vigilantism);

• internal connection between the act and desired outcome;

• effect on constitutional rights;

• legally relevant (not merely morally questionable) actions;

• individual autonomy (it is not unlawful if the act is considered an autonomous decision and is not required by the law);

• the factors listed in sub-section (4) are considered especially grave; and

• the context of the action/circumstances of the case.

• It is controversial whether long-term objectives of an act (e.g. environmental protection in violent demonstration cases) are legally relevant to determining if the definition of the crime is met; the majority does not consider them.¹⁰

Once the definition of ‘force’ is met, then one must weigh up the relevant factors against each other to determine whether the ‘force’ is unlawful under section 240. Each of the factors set out earlier may not be individually sufficient or even necessary conditions for an act to meet the definition of Nötigung. To give some examples of the way that this balancing act has been carried out by the German courts:¹¹

• Loading and aiming a gun to scare people away constitutes ‘force’. It is unlawful if one could have requested assistance from the police in time (priority of public authority). Another factor is the potential danger of a gun and the violation of the law which forbids the possession of firearms.¹²

• Turning off the heating of an apartment can be an unlawful use of force or threat of harm. It is to be considered that cold temperatures can have deleterious effects on health and make the apartment uninhabitable. Another relevant aspect is whether or not the claim (here, the rent) is disputed.¹³

• With respect to a sit-in protest: To determine lawfulness, it is to be considered whether the protest is protected by the right to freedom of speech and/or freedom of assembly. Furthermore, a road blockade which only lasts for one minute is of such a short duration that it may not be punishable. Another factor is whether all or only some entrances are affected. It was also considered that the only people affected were those against whom the protest was directed.¹⁴

• A ‘tailgating-case’: Here, the court considered the danger of the behaviour with respect to important legal rights (i.e. possible traffic accident, because the car probably could not stop in time). The motive of the tailgating (to be able to drive slightly faster) was unreasonable. Another factor was again the duration of the dangerous act.¹⁵

In each of these cases, the factors identified earlier are not explicitly weighed up against each other in detail. Rather, the relevant factors in the specific case are identified, and the court determines whether these factors are sufficient to meet the requirements for an unlawful use of force for the crime of Nötigung.

Type Theory and ‘Use of Force’

It is proposed that a prohibited ‘use of force’ between States within the meaning of article 2(4) of the UN Charter is a type rather than a concept; that is, it is characterised by a basket of elements, not all of which must necessarily be present for an act to meet the definition. Instead, these elements are identified and weighed up to determine whether the threshold of the definition of ‘use of force’ is met. In other words, individually each of these elements may not be necessary, but in a given case a particular combination of them may be jointly sufficient to constitute a prohibited ‘use of force’. If some elements are weak, but other elements are of a higher gravity/intensity, then the balancing of the elements under the particular circumstances may result in an act meeting the definition of an unlawful ‘use of force’ under article 2(4). As with the crime of Nötigung, there are two kinds of elements to weigh up to determine whether an act constitutes an unlawful ‘use of force’ under article 2(4): firstly, those relating to whether an act is a ‘use of force’, and, secondly, contextual elements that must be present for that ‘use of force’ to fall within the scope of article 2(4) and thus be unlawful under that provision.

Accordingly, if a ‘use of force’ is a type, then all ‘uses of force’ share elements in common; however, for an act to fall within the definition of ‘use of force’, it does not have to display all elements. The consequence of this is that there will be several different types of ‘use of force’, for example, classical uses of force employing armed force of a high gravity (bombardment, invasion against opposition), as well as uses of force that do not employ physical/armed force, such as an unresisted invasion or occupation. This theory is supported by the analysis of anomalous examples of ‘use of force’ and non-‘use of force’ in Chapter 7, which has demonstrated that each of the elements of a ‘use of force’ must not always be present for an act to constitute an unlawful ‘use of force’. Putting it all together, it is apparent that none of the elements of a ‘use of force’ identified in Part II are strictly necessary for an act to meet the definition, except for the object/target of the use of force (as explained in Chapter 4 with respect to ‘international relations’, a nexus is probably required between the object or target of the ‘use of force’ and another State). The examples of ‘use of force’ which disprove the necessity of each of the elements of a prohibited ‘use of force’ are summarised as follows:

• Physical force: Military incursion without recourse to the use of weapons, unresisted invasion or military occupation, unconsented mere presence. Controversial: cyber operations, non-kinetic non-cyber operations.

• Physical effects: As earlier. Although there are ‘uses of force’ which do not have any physical effects, to be legally relevant to the equation of whether an act is a ‘use of force’, any effects must be physical and direct (no intermediate steps between the act and its result). In other words, although a physical effect is not necessary for an act to constitute an unlawful ‘use of force’, non-physical and non-direct effects will not be relevant to the calculation. As discussed in Chapter 6, it is legally uncertain whether the physical effects must actually ensue (as opposed to merely potential effects), and if they must be permanent.

• Gravity: As discussed in Chapter 6, it is legally uncertain if there is a lower gravity threshold for an act to fall within the scope of the jus contra bellum. However, since even a single shot fired across the border by the military of one State could be considered an unlawful ‘use of force’, this appears to negate the argument that there is a gravity threshold for a prohibited ‘use of force’ under article 2(4).

• Intent: As discussed in Chapter 6, although it is legally uncertain, it seems that even an accidental use of force could be considered a violation of article 2(4) of the UN Charter under certain circumstances, such as ‘the accidental projection of armed force … across a border’ (e.g. shots or shells fired).¹⁶

This disproves the null hypothesis (the commonly accepted position which, if proven, would disprove the alternative hypothesis) that a ‘use of force’ is not a type but a concept, for which there is a checklist of fixed elements that must always be present for the definition to be met. Rather, determining that an act meets the definition of a ‘use of force’ is not a matter of going through a checklist of elements to see whether every element is present. Instead, it is an equation that must be weighed up.

On the basis of this type hypothesis, two kinds of elements are proposed that indicate an unlawful ‘use of force’ under article 2(4): firstly, elements relevant to whether the act is a ‘use of force’, and, secondly, contextual elements that are required to bring the ‘use of force’ within the scope of article 2(4) and render it unlawful. Since the latter are fundamental requirements, they are dealt with first:

1. (1) Fundamental requirements (contextual elements): These are the necessary (but insufficient) contextual elements to bring a ‘use of force’ within the scope of article 2(4). These elements must always be present for an act to constitute an unlawful ‘use of force’ in violation of article 2(4), but on their own they will not suffice for an act to violate that provision (since it must also meet the definition of ‘use of force’). ‘Threat of force’ is not considered here, but in respect of ‘threats of force’ under article 2(4), the same framework of analysis would apply with respect to the contextual elements.¹⁷ These fundamental requirements follow explicitly from the text of article 2(4) itself, such as:

   • two or more States;

   • international relations;

   • ‘against the territorial integrity or political independence of any state or in any other manner inconsistent with the Purposes of the United Nations’.

Each of these elements is discussed in further detail in Chapter 4.

1. (2) Elements that indicate that an act is a ‘use of force’: These relate to the meaning of ‘use of force’ rather than to the other terms of article 2(4). These elements are more likely to be based on subsequent agreement or subsequent practice (rather than the contextual requirements which are more likely to be text-based), since they do not come from a plain reading of the text of article 2(4) (or are not explicit) but are the result of a shared understanding of the parties to the UN Charter. These may include the following elements identified in Chapters 5 and 6:

   • Means: Physical force

   • Physical Effects:

     • Direct physical effects

     • Permanent versus temporary

     • Actual versus potential

   • Object/target: In particular, the required nexus to a State. For non-State objects/targets that do not have a close association with a State, more will be required to bring the act within the scope of article 2(4), such as the presence of other factors including possibly the gravity of the (potential) effects, a pre-existing dispute between States or a coercive intent against a State.

   • Gravity of effects: Noting again that the question of whether there is a de minimis gravity threshold is not solved by the text of article 2(4), which neither specifies nor excludes a gravity threshold for a use of force to fall within the scope of the prohibition. As discussed in Chapter 7, any such threshold may also differ by domain.

   • Hostile intent: The text of article 2(4) strongly indicates that at the very least, an intended action is required. The text does not explicitly require or exclude an intended effect, although State practice indicates that mistaken forcible acts are usually not treated as violating the prohibition of the use of force. There is textual support for the position that a coercive intent is required under article 2(4), due to the relationship between the prohibition of threats and uses of force; the relationship of the non-intervention principle and the principle of the non-use of force; and the object and purpose of the prohibition of the use of force in article 2(4).

Other relevant indicative factors that may relate to one or more of the aforementioned elements are:

• Type of weapon: The type of weapon employed could be relevant to the gravity of the (potential) effects and also to whether the ‘use of force’ is perceived to be in ‘international relations’, since certain sophisticated weapons could only have been developed by States and are not easily available to other actors, thus making it more likely for the victim State to conclude attribution and hostile intent. An example is the use of the chemical weapon Novichok in the Skripal assassination attempt, discussed in Chapter 6 and later in this chapter.

• Political context: As discussed in Chapter 4, the political context of a forcible act, such as whether there is a pre-existing political dispute, influences its characterisation as a violation of article 2(4). This relates to the contextual elements of prohibited force since the presence of a political dispute may bring an act within the realm of international relations and a use of force between States. It may also relate to elements relevant to whether the act is a ‘use of force’, such as gravity (e.g. by increasing the perceived level of security threat to the State) and intention (by demonstrating a hostile/coercive intention, or at the very least, an intention to influence or resolve a political dispute using force).

• Who carries out the forcible act: It is relevant whether the forcible act is carried out by military or police/other traditional law enforcement bodies, for example, the coast guard.¹⁸ This is relevant not only in terms of attribution but also to the perception by the other State with respect to the perceived military nature of the act, and may also be relevant to the assessment of gravity and intent. Due to grey zone operations, this could become increasingly relevant, for example, the use of maritime militia in the South and East China Seas.¹⁹

• Location of forcible act: It is also relevant to the assessment of whether an act constitutes a prohibited ‘use of force’; whether the conduct and/or its effects occur within or outside a State’s own territory (on land, sea or air respectively); within a third State’s territory (land, sea or air); in disputed territory or in zones to which special legal rules apply such as a State’s Exclusive Economic Zone, the high seas, international airspace, outer space or terra nullius. This is relevant not only to the applicable legal framework and jurisdiction but also to the ‘international relations’ aspect of the article 2(4) prohibition, and potentially also gravity (due to differences in potential threat or the type of force that is possible in each domain).

According to the type theory proposed here, the aforementioned elements must be identified, weighed and balanced to determine whether an act is a prohibited ‘use of force’ under article 2(4) and may be combined in different permutations to produce different types of ‘use of force’ which may not share all of the same elements. Part of such a balancing and weighing exercise implies that the weaker certain elements are, the higher the number or gravity/intensity of the other elements must be in order for the act to constitute a prohibited ‘use of force’.

Applying Type Theory to Anomalous Examples of ‘Use of Force’

As discussed in detail in Chapter 7, there are several well-known and accepted ‘uses of force’ that violate the prohibition in article 2(4) but do not conform to all of the criteria normally associated with a ‘use of force’, namely, physical means and/or physical effects. These examples, taken from the 1974 Definition of Aggression,²⁰ include invasion and military occupation (article 3(a)), blockade (article 3(c)), mere presence in violation of a Status of Forces Agreement (SOFA) (article 3(e)) and indirect use of force either through inter-State assistance (article 3(f)) or through non-State armed groups (article 3(g)). Other, lower gravity, examples discussed in Chapter 7 include intentionally crossing a border bearing arms with an intention to use them even before any weapons are actually fired and aerial incursion. Applying the type theory framework to these anomalous examples of ‘use of force’ helps to identify and explain why these are indeed unlawful ‘uses of force’. The analysis results in the following two types of ‘use of force’ which display a different combination of elements, and highlights a unique third category of ‘use of force’ that is the result of subsequent agreement.

1. Military Incursion without Recourse to the Use of Weapons

Examples: unresisted invasion, military occupation (article 3(a) of the 1974 Definition of Aggression), intentionally crossing a border bearing arms with an intention to use them even before any weapons are actually fired, aerial incursion.

Contextual elements:

• Political context: In clear-cut cases (such as invasion and military occupation), the use of force occurs in the context of a political dispute and is clearly in ‘international relations’.

Elements of ‘use of force’/indicative factors:

• Lack of physical means.

• Lack of physical effects but high potential effects if escalation occurs.

• Actor: Military units, indicating a clearly implied intention to use force if resisted (hostile intent, possibly coercive intent depending on context).

• Location: Within the territory (including airspace) of another State, constituting a violation of sovereignty and territorial integrity and a high threat of escalation to physical means and physical effects on the territorial State.

2. Unconsented Presence in Territory

Examples: the blockade of the ports or coasts of a State by the armed forces of another State (article 3(c) of the 1974 Definition of Aggression); the use of armed forces of one State which are within the territory of another State with the agreement of the receiving State, in contravention of the conditions provided for in the agreement or any extension of their presence in such territory beyond the termination of the agreement (article 3(e) of the 1974 Definition of Aggression).

Contextual elements:

• Political context: In clear-cut cases (blockade), the use of force occurs in the context of a political dispute and is clearly in ‘international relations’. In the less clear-cut case of overstaying in violation of a Status of Forces Agreement, the political context may be a decisive factor in the characterisation of the act as a prohibited ‘use of force’ by indicating if the act is one in ‘international relations’ and if there is a hostile/coercive intent.

Elements of ‘use of force’/indicative factors: As in the previous example, there is a lack of physical means and physical effects, but the following elements and indicative factors are present:

• Actor: Military units, indicating an implied intention to use force if resisted (hostile intent, possibly coercive intent depending on context).

• Location: Within the territory (including airspace) of another State, constituting a violation of sovereignty and territorial integrity and a threat of escalation to physical means and physical effects on the territorial State.

3. Special Case: Indirect Use of Force

Examples: The action of a State in allowing its territory, which it has placed at the disposal of another State, to be used by that other State for perpetrating an act of aggression against a third State (article 3(f) of the 1974 Definition); the sending by or on behalf of a State of armed bands, groups, irregulars or mercenaries, which carry out acts of armed force against another State of such gravity as to amount to the acts listed earlier, or its substantial involvement therein (article 3(g) of the 1974 Definition).

Unlike the previous examples, due to the lack of both direct physical means or direct physical effects, this category of unlawful ‘use of force’ appears to really be an agreed special case rather than meeting the definition through a combination of elements that reaches a particular threshold. Thus, indirect force, unlike the other types of force discussed in this chapter, is a result of subsequent agreement between States regarding the interpretation of article 2(4) of the UN Charter to cover certain forms of indirect force.

Illustrative Examples of Balancing the Elements of a ‘Use of Force’

Applying type theory to specific instances of inter-State ‘use of force’ further illustrates the notion of weighing the various elements of a prohibited ‘use of force’ to determine why some of these incidents were characterised by States as an unlawful ‘use of force’ and other similar incidents were not. Here, we will focus on the object/target of a use of force to explain why one attempted killing – that is, a forcible act with potential but unrealised effects (the attempted killing of George Bush) – was regarded by several States as an unlawful use of force but another (Sergei Skripal) was not. We will also examine excessive or unlawful maritime law enforcement to identify why some incidents (the Mayaguez incident, the Germany/Iceland Fisheries Jurisdiction case and Guyana/Suriname) were characterised as an unlawful ‘use of force’ whereas similar incidents (Red Crusader, Torrey Canyon, Rainbow Warrior and M/V Saiga (No. 2)) were not. As well as their explanatory purpose to show how type theory can help to clearly identify why particular incidents are or are not an unlawful ‘use of force’, these examples highlight the relationship between particular elements of a ‘use of force’.

Potential Effects, Object/Target and Intention

A use of force with only potential but unrealised effects may require a higher level of (potential) gravity, intention, or an object/target that has a particularly close connection to another State (such as Foreign Minister/President) in order to be characterised as unlawful under article 2(4) of the UN Charter. Although these elements are elements of a ‘use of force’, they may also relate to the contextual element of whether the act is in ‘international relations’. This is illustrated through the juxtaposition of States’ legal characterisation of two attempted killings: that of former US President George Bush in 1993 and of the former Russian intelligence officer Sergei Skripal in England in 2018.

In the first incident, the Iraqi Intelligence Service (IIS) allegedly directed and carried out an attempted assassination of former US President George Bush by planning to explode a car bomb next to his motorcade on a visit to Kuwait from 14 to 16 April 1993.²¹ In response, from 26 to 27 June 1993, the United States retaliated by launching twenty-three Tomahawk missiles against the headquarters of the IIS in Baghdad, destroying the building, killing at least six civilians and injuring twenty others. To justify the strike, the United States referred to article 51 of the UN Charter and stated that it was exercising the ‘right to self-defence by responding to the Government of Iraq’s unlawful attempt to murder the former Chief Executive of the United States Government, President George Bush’.²² The international response to the US action was mixed.²³ However, some States that expressed support or understanding for the US action referred expressly to the nature of the target of the assassination attempt, including Japan, Brazil, New Zealand and Spain.²⁴ In particular, New Zealand asserted that ‘any nation that seeks to assassinate the Head of State or a member of the senior political leadership of another State commits an act of aggression. Such actions are at the most serious end of the scale because Heads of State symbolize the sovereignty and integrity of their country’.²⁵ Some scholars also ‘emphasized that the protection of a state’s elected officials would be an essential attribute of state sovereignty, especially taking into account the destabilizing effects that an assassination of a Head of State could have on the nation’.²⁶ Thus, although the international response to the incident was ‘not unanimous and in most cases not unequivocal’²⁷ regarding the US self-defence claim, what matters for our purposes is the characterisation of the attempted killing itself as an unlawful use of force on the basis of the close nexus between the target and the victim State even though the intended harmful effect did not materialise.

In contrast, the attempted killing of Sergei Skripal in the UK by suspected Russian agents shows that when there is a relatively low nexus with the territorial State, the attempted killing of an individual by foreign State agents is not enough on its own for States to widely characterise the incident as an unlawful ‘use of force’ in violation of article 2(4). Mr Skripal (apparently a dual Russian/UK national and former double agent)²⁸ and his daughter Yulia were found unconscious on a bench in Salisbury and later hospitalised in serious condition together with an attending police officer. The United Kingdom alleged that a military-grade Novichok nerve agent of a type developed by Russia was used in the attack and accused Russia of being responsible for carrying out the attack. The Russian government denied any involvement.²⁹ Despite the use of a chemical weapon allegedly by Russian agents on the territory of the United Kingdom, the attempted killing was not widely denounced as a violation of article 2(4), possibly because of the lack of a particularly close connection between Mr Skripal and the territorial State. For such targets that do not have a close association with a State, other elements of a ‘use of force’ must be more serious to bring the act within the scope of article 2(4), such as the gravity of the (potential) effects, a pre-existing dispute between States or a coercive or hostile intent against a State. In this case, the UK emphasised the gravity of the potential effects of the chemical weapon on the wider public when claiming that the attack on Mr Skripal was an unlawful use of force in violation of article 2(4).³⁰ This incident is analysed in more detail as a case study to illustrate the application of type theory later in this chapter.

‘International Relations’, Gravity and Intention

As argued in Chapter 6, the elements of ‘international relations’, gravity and intention are interrelated. This is illustrated in the following case study on excessive or unlawful maritime law enforcement and ‘use of force’. With respect to excessive maritime law enforcement, there is mixed practice in this regard. First of all, why would a use of force against a civilian vessel registered to another State be considered ‘force’ under article 2(4) at all? The reason is the principle of exclusive flag State jurisdiction – a use of force against a civilian vessel by a non-flag State is the exercise of enforcement jurisdiction within a domain subject to the exclusive jurisdiction of another State. It may therefore under certain circumstances fall under ‘international relations’ and be considered to be against the sovereignty of another State (i.e. the flag State). It is important to note that different international law principles apply to use of force in law enforcement versus a use of inter-State force under the jus contra bellum.³¹ Patricia Jiminez Kwast makes the important point that there are two separate issues: which legal category applies (law enforcement or use of force), and whether the act complies with the lawful requirements of that category – just because law enforcement action is unlawful under that framework does not automatically render it a violation of the prohibition of the use of force.³² Tom Ruys posits that

[a]n argument could therefore be developed that enforcement action undertaken by the territorial state within its territory or, by extension, against merchant vessels in relation to a coastal state’s Exclusive Economic Zone or continental shelf – even if the action is tainted by illegality – is presumed not to affect the international relations between those states and accordingly remains beyond the reach of Article 2(4). Only if it appears from the circumstances of the case that the force used ‘directly arises from a dispute between sovereign States’ will this presumption be rebutted.³³

In light of the increasing constabulary role of navies, especially in the South and East China Seas, the distinction between these two applicable legal frameworks and their boundary is of particular relevance.³⁴

State practice shows that States do sometimes consider purported maritime law enforcement to be a use of force. There are numerous examples in State practice where forcible acts at sea were characterised by States as a violation of article 2(4): the 1975 Mayaguez incident (self-defence); the Germany/Iceland Fisheries Jurisdiction case (Germany claimed a violation of article 2(4), although the Court did not rule on this point); the Canada/Spain Fisheries Jurisdiction case (Spain claimed a violation of article 2(4), but the Court held it had no jurisdiction – discussed in Chapter 7); and the Guyana/Suriname arbitration. However, State practice is not consistent and numerous similar incidents have not been characterised as an unlawful use of force under article 2(4). These include the 1962 Red Crusader (Denmark/UK) case, the 1967 Torrey Canyon incident, the 1985 Rainbow Warrior incident and the 1997 M/V Saiga (No. 2) incident. It is therefore instructive to examine these incidents through the lens of type theory (i.e. the identification and balancing of the elements of a ‘use of force’) to see why only some of these incidents were characterised as an unlawful ‘use of force’.

Excessive Maritime Law Enforcement

The Mayaguez incident in 1975 occurred in the context of the Vietnam War and the recent ousting of the US-backed Khmer Republic by the Khmer Rouge. The US-flagged container ship the Mayaguez and its crew were seized by Cambodian naval forces within Cambodian territorial waters, although the United States disputed the twelve nautical mile rule at the time. During the seizure of the vessel, the Khmer Rouge naval vessel fired a machine gun and then a rocket-propelled grenade across the bow of the ship before boarding and seizing the vessel.³⁵ The United States launched a rescue operation, citing article 51 of the UN Charter.³⁶ The seizure of the Mayaguez was thus considered an unlawful ‘use of force’ (and ‘armed attack’) by the United States, giving rise to a right to self-defence. In this incident, the target of the use of force had a strong connection to the victim State (given the political context) and due to the surrounding events, the forcible act evinced a hostile intent and was clearly in the ‘international relations’ between the two States concerned. Thus, the contextual elements of an unlawful ‘use of force’ were present. In terms of elements of ‘use of force’, the gravity of the physical means was moderate, as was the gravity of the physical effects (the seizure of the vessel and its crew).

In contrast, in the Red Crusader incident in 1962, maritime law enforcement was found to be excessive and unlawful but was not characterised as a violation of article 2(4) of the UN Charter. In that incident, Danish authorities arrested a British-flagged vessel in Danish territorial waters and fired shots at the vessel without warning. The International Commission of Inquiry found:³⁷

In opening fire at 03.22 hours up to 03.53 hours, the commanding officer of the Niels Ebbeen exceeded legitimate use of armed force on two counts: (a) firing without warning of solid gun-shot; (b) creating danger to human life on board the Red Crusader without proved necessity, by the effective firing at the Red Crusader after 03.40 hours.³⁸

Similarly, in the 1997 M/V Saiga (No. 2) incident, maritime law enforcement was found to be excessive but not an unlawful ‘use of force’ under article 2(4) of the UN Charter. In that incident, Guinea arrested a vessel flagged to St Vincent and the Grenadines within the Exclusive Economic Zone of Guinea, injuring at least two crew members. St Vincent and the Grenadines did not claim that it was a violation of article 2(4) but of the UN Convention on the Law of the Sea³⁹ (UNCLOS) articles 56(2) and 58, 111, 292 (freedom of navigation, violation of hot pursuit conditions and prompt release). The International Tribunal for the Law of the Sea also did not raise article 301 of UNCLOS nor article 2(4) of the UN Charter. The Tribunal instead applied the requirements for lawfulness of use of force in law enforcement measures:⁴⁰

In considering the use of force used by Guinea in the arrest of the Saiga, the Tribunal must take into account the circumstances of the arrest in the context of the applicable rules of international law. Although the Convention does not contain express provisions on the use of force in the arrest of ships, international law, which is applicable by virtue of article 293 of the Convention, requires that the use of force must be avoided as far as possible and, where force in unavoidable, it must not go beyond what is reasonable and necessary in the circumstances. Considerations of humanity must apply in the law of the sea, as they do in other areas of international law. These principles have been followed over the years in law enforcement operations at sea.

In the Red Crusader and M/V Saiga (No. 2) incidents, it is not apparent that the vessels were targeted due to their nationality nor in the context of a political dispute between the States concerned. There was no apparent coercive or hostile intent against the flag State, given that Denmark and Guinea respectively were enforcing domestic laws within their own territorial sea (in the case of the Red Crusader) or Exclusive Economic Zone (in the case of the M/V Saiga (No. 2). As the forcible act did not occur in the international relations between the States concerned, the contextual elements of an unlawful ‘use of force’ are missing. In terms of elements of ‘use of force’, the physical means employed and their physical effects were of relatively low gravity. This coupled with a low nexus and a lack of hostile intent against another State results in an insufficient combination of elements of a ‘use of force’ including their relative weight. Accordingly, these two incidents were deemed to fall within the realm of law enforcement rather than the jus contra bellum.

Maritime Law Enforcement with No Basis for Jurisdiction

In contrast to the previous incidents which involved excessive maritime law enforcement, the following category of incidents involved the purported exercise of law enforcement against foreign-flagged vessels with no (or a disputed) basis for jurisdiction because it took place in the territorial waters of another State, on the high seas or in a disputed maritime zone.

In the incidents of the Fisheries Jurisdiction case (Germany v Iceland) and the Guyana v Suriname arbitration, the purported maritime law enforcement by Iceland and Suriname respectively were characterised by the ‘victim’ State as either an unlawful use or threat of force. These incidents both occurred in disputed maritime zones. In the former case, Iceland sought to unilaterally extend its fisheries jurisdiction to fifty miles from the baseline. Germany challenged this and claimed that Iceland’s actions in enforcing this extended fisheries jurisdiction zone against German fishing vessels by cutting their nets and firing warning shots and live rounds was a violation of article 2(4) of the UN Charter.⁴¹ The International Court of Justice (ICJ) did not analyse Germany’s submission regarding use of force in substance. Instead, it made a finding on procedural grounds that it was unable to accede to the submission, since it was not put in concrete terms seeking specific damages with evidence to support each claim.⁴² In the case of Guyana v Suriname in 2007, Guyana claimed that the Surinamese navy had violated article 2(4) of the UN Charter by ordering an oil rig and drill ship operating under licences issued by Guyana to leave the disputed maritime zone in which they were operating.⁴³ The tribunal held that ‘the action mounted by Suriname on 3 June 2000 seemed akin to a threat of military action rather than a mere law enforcement activity’.⁴⁴

Applying type theory to these incidents, they were each characterised by the other State (and by the arbitral tribunal in Guyana v Suriname) as a use or threat of force despite the relatively low gravity of each incident in terms of their physical means and effects. One explanation is that since each incident took place within a disputed maritime zone and as a means of enforcing the State’s claim to that zone, it was a coercive measure in the ‘international relations’ between the respective States. Thus, even incidents of low gravity in physical means and physical effects may suffice to meet the definition of unlawful use or threat of force when combined with a clear coercive intent and when the incident clearly takes place within ‘international relations’.

In contrast, the incident of the Torrey Canyon in 1967, in which the British RAF dropped napalm bombs on a Liberian-flagged oil tanker which ran aground on the high seas (discussed in the Chapter 7), was not characterised as an unlawful ‘use of force’ despite the lack of legal grounds for the UK to exercise law enforcement jurisdiction against the vessel to prevent marine pollution under either treaty or customary international law. Clearly, a high gravity of physical means and physical effects were present in this case. One basis for the lack of any invocation of article 2(4) in relation to this incident could be that the contextual requirement of ‘international relations’ was missing. Given that the UK had a clear and limited intention to release and burn the remaining oil in the vessel’s tanks to prevent marine pollution on the high seas (an intention that was accepted as legitimate by the international community as a whole, as demonstrated by the subsequent adoption of the International Convention on Intervention on the High Seas in Cases of Oil Pollution Casualties⁴⁵ to permit this type of action), and the application of force, though deliberate, was not coercive or hostile with respect to the flag State, it was not regarded by any State to engage the ‘international relations’ between the UK and the flag State of the vessel, Liberia, or any other State.⁴⁶

In the Rainbow Warrior affair, on 10 July 1985, on official orders, French secret service agents carried out an attack against a British-flagged civilian (Greenpeace) vessel moored in the internal waters of New Zealand. Two high explosive devices detonated and sunk the vessel, killing a Dutch citizen who was on board.⁴⁷ The New Zealand government argued that the attack against the Rainbow Warrior was a ‘serious violation of basic norms of international law … specifically, it involved a serious violation of New Zealand sovereignty and of the Charter of the United Nations’ and sought reparations.⁴⁸ However, New Zealand did not allege a violation of article 2(4). Olivier Corten argues that this is probably because the operation was limited in scope and was not ordered by ‘the highest echelons of the State’.⁴⁹ Applying type theory analysis to this incident, we can see that the attack clearly took place in the ‘international relations’ between the two States since it was officially ordered and carried out by French government agents and constituted a serious violation of the sovereignty of New Zealand. However, there was no hostile or coercive intention vis-a-vis New Zealand and although the physical means employed were of relatively high gravity, the physical effect on the ‘victim’ State (New Zealand) was confined to a violation of sovereignty, since the vessel was British-flagged and the person killed in the attack was of Dutch nationality. As such, New Zealand did not treat the matter as an unlawful ‘use of force’ against it but as a domestic crime (by the secret service agents who carried out the attack) and a violation of its sovereignty by France.

This conclusion has implications for a wider debate under jus in bello regarding whether ‘non-consensual force against a non-State actor on the territory of another State is always an [International Armed Conflict (IAC)], as opposed to those who say it is only sometimes an IAC, depending on the circumstances’.⁵⁰ The classification of conflict under jus in bello is a separate question to whether an act is a prohibited ‘use of force’ under jus contra bellum and is relevant to whether (and which) rules of international humanitarian law (IHL) apply to the conduct of hostilities. The International Committee of the Red Cross (ICRC) appears to take the first position set out earlier, stating that an IAC ‘arises between the territorial State and the intervening State when force is used on the former’s territory without its consent’.⁵¹ The benefit of this approach is that it provides legal certainty regarding the classification of conflict and applicability of IHL rules to ensure protection. Others such as Noam Lubell point out the absurdity of applying this approach to incidents such as the sinking of the Rainbow Warrior since this would lead to the conclusion that there was an IAC between France and New Zealand, which ‘would … seem incongruous with the notion of IAC’ and lead to inappropriate application of IHL rules to the situation.⁵² The conclusion of the type theory analysis in this chapter that the sinking of the Rainbow Warrior was not a ‘use of force’ under article 2(4) of the UN Charter allows a way out of the impasse and has the potential to provide clarity to the debate on classification of conflict under jus in bello when States use force against non-State actors on the territory of another State. A more detailed analysis of the relationship between ‘use of force’ under jus contra bellum and classification of conflict under jus in bello is beyond the scope of this book.

Case Study: The Attempted Killing of Sergei Skripal

The final part of this chapter sets out a detailed analysis of two illustrative examples in order to demonstrate how to apply type theory to a specific incident. The first case study that will be analysed is the killing of Sergei Skripal in the UK in 2018. The second case study concerns the use of force in outer space. This exercise will show the usefulness of type theory for analysing controversial or borderline incidents and demonstrate how to apply it in concrete cases, as well as highlighting the open questions and challenges involved.

Facts and Legal Claim

As briefly discussed earlier in this chapter, Mr Skripal, a former Russian double agent,⁵³ was the subject of an attempted assassination in Salisbury in the United Kingdom in 2018 using a military-grade nerve agent, Novichok. Traces of the nerve agent Novichok were later discovered at nine sites around Salisbury, with the highest concentration on the doorknob of Mr Skripal’s home.⁵⁴ A UK police investigation identified two Russian military intelligence officers as the main suspects in the attack on Mr Skripal.⁵⁵ The United Kingdom accused Russia of the attempted killing, with the Russian government denying involvement in the attack.

In a statement to the House of Commons on 14 March 2018, UK Prime Minister Theresa May said that the UK government had given Russia one day to account for the incident and stated: ‘Should there be no credible response, we will conclude that this action amounts to an unlawful use of force by the Russian State against the United Kingdom. … this attempted murder using a weapons-grade nerve agent in a British town was … an indiscriminate and reckless act against the United Kingdom, putting the lives of innocent civilians at risk.’⁵⁶ On 14 March 2018, the UK Ambassador Jonathan Allen, in a briefing to the UN Security Council, stated that the UK ‘conclude[d] that the Russian State was responsible for the attempted murder of Mr Skripal and his daughter, and Police Officer Nick Bailey, and for threatening the lives of other British citizens in Salisbury’ and described it as ‘an unlawful use of force – a violation of article two of the United Nations charter, the basis of the international legal order’.⁵⁷

Applying type theory to the Skripal incident shows that the contextual elements in this incident are factually contentious, whereas the elements of a ‘use of force’ are legally contentious. The systematic application of type theory highlights that the crux of the matter is whether the potential effects of the purported use of force suffice to render the act a violation of jus contra bellum.

Contextual Elements

• Two or more States: If, as the UK claimed, Russia was responsible for the attack, then this contextual element is fulfilled. Of course, this would need to be substantiated by evidence and fulfil the attribution requirements under international law.⁵⁸ For the purposes of this analysis, we will leave these aside in order to focus on the legally contentious aspects of the incident.

• In their ‘international relations’: Again, proceeding on the assumption that the attack is attributable to Russia, the use of a prohibited nerve agent on the territory of another State to carry out a targeted killing is clearly in ‘international relations’.

• ‘[A]gainst the territorial integrity or political independence of any state or in any other manner inconsistent with the Purposes of the United Nations’: A targeted killing by a State on the territory of another State violates the territorial integrity of that State. It is also inconsistent with the Purposes of the United Nations (namely, respect for human rights: Article 1(3) of the Charter).

Accordingly, if the attack is attributable to Russia, all contextual elements of a prohibited ‘use of force’ are fulfilled.

Elements of Prohibited Force

• Means: No physical force was employed, but the weapon used was a prohibited military-grade chemical nerve agent, Novichok.

• Physical effects: The Novichok attack had direct physical effects on at least four people who fell critically or seriously ill: Sergei Skripal, his daughter Yulia Skripal and two police officers involved in the investigation of the attack. Months after the attack, two more individuals in Salisbury suffered physical effects after coming into contact with the container used to carry the nerve agent, one of whom died.⁵⁹ In addition to the direct physical effects, the use of the highly toxic chemical weapon Novichok carried a risk of potential harm to the wider public due to nature of the weapon, which was used in a public location and can reportedly persist for long periods.⁶⁰

The UK emphasised the potential effects of the attack at the UN Security Council, namely, that ‘British Police Officer Nick Bailey, was … exposed and remains in hospital in a serious condition. Hundreds of British citizens have been potentially exposed to this nerve agent in what was an indiscriminate and reckless act against the United Kingdom.’⁶¹ Marc Weller argues that the UK’s position is implicitly that ‘any use of toxins would amount to a use of force, due to their potential (rather than actual) widespread and indiscriminate effects’.⁶²

• Object/target: The attack took place in the United Kingdom town of Salisbury. The target of the forcible act, Sergei Skripal, was a Russian double agent convicted of spying for the United Kingdom and relocated there in 2010 as part of a prisoner swap, later gaining UK citizenship.⁶³

• Gravity of effects: The actual effects were relatively low in gravity but there was a potential for high gravity of effects, as set out earlier.

• Hostile intent: There is no evidence that the attack manifested a hostile intent against the United Kingdom rather than against the individual target of the attack due to his prior conviction in Russia of spying.

Conclusion

Assuming that the attack was attributable to Russia, then the contextual elements are present which would bring the attack within the scope of article 2(4) of the UN Charter. The following elements of a ‘use of force’ are present: means (prohibited chemical weapon), direct physical effects with low gravity but very grave potential effects. Conversely, the target of the attack, Mr Skripal, did not have close ties to the territorial State; the actual gravity of the attack was relatively low and there was no evidence of a hostile intent by Russia against the United Kingdom. For the United Kingdom (the only State to characterise the attempted killing as a prohibited use of force), it appears that the decisive element was the use of a prohibited chemical weapon on its territory which carried a risk of grave harm to the wider public. This characterisation is plausible, but it is a borderline case because none of the other elements of a ‘use of force’ were particularly pronounced. In the absence of a closer connection between the target of the forcible act and the territorial State, a hostile intent or more widespread harm directly caused by the nerve agent, in this author’s view, the attempted killing of Sergei Skripal was not a prohibited use of force against the United Kingdom. Nevertheless, this incident provides an illustration of how the type of weapon and potential harm may be considered as relevant factors in an assessment of legality under article 2(4).

Case Study: Use of Force in Outer Space

The second case study to demonstrate how to apply type theory and its utility concerns the use of force in outer space. Outer space has been militarised since the late 1950s and is becoming an increasingly important military domain. In 2019 NATO declared outer space to be an operational domain,⁶⁴ and a growing number of States have since established a military space force or expanded existing military branches to cover outer space.⁶⁵ Space capabilities have important military functions, including for navigation, surveillance, communications, situational (battlefield) awareness and targeting.⁶⁶ Military uses of outer space at present principally concern satellites, which are potentially threatened by the testing and use of anti-satellite (ASAT) and other space weapons and their stationing (potentially, in some instances) in outer space. The Gulf War is regarded as the first space war due to the heavy reliance by Allied States on space-based military assets against Iraq.⁶⁷ Critical civilian infrastructure and services also increasingly rely on space systems, including infrastructure essential for food production, health care, disaster relief, transport, communication, energy and trade, environmental science and the global navigation satellite systems such as GPS, which themselves underpin global communication networks, banking and financial markets and energy grids.⁶⁸ At the 2021 Brussels Summit, NATO leaders recognised that ‘attacks to, from, or within space present a clear challenge to the security of the Alliance, the impact of which could threaten national and Euro-Atlantic prosperity, security, and stability, and could be as harmful to modern societies as a conventional attack’.⁶⁹

The prohibition of the threat or use of force in article 2(4) of the UN Charter applies in outer space. The applicability of international law, including the UN Charter, to activities in outer space is recognised in article III of the Outer Space Treaty⁷⁰ (OST) as well as article 3(2) of the Moon Agreement,⁷¹ and in relevant UN General Assembly resolutions.⁷² Article III of the OST provides: ‘States Parties to the Treaty shall carry on activities in the exploration and use of outer space, including the moon and other celestial bodies, in accordance with international law, including the Charter of the United Nations, in the interest of maintaining international peace and security and promoting international co-operation and understanding.’ Article 3(2) of the Moon Agreement is more explicit and provides: ‘Any threat or use of force or any other hostile act or threat of hostile act on the moon is prohibited. It is likewise prohibited to use the moon in order to commit any such act or to engage in any such threat in relation to the earth, the moon, spacecraft, the personnel of spacecraft or man-made space objects.’⁷³ However, as on Earth, there is no agreed definition of a prohibited use of force in space.⁷⁴ The application of the prohibition of the use of force in outer space faces special challenges due to the unique environment of outer space and the types of ‘use of force’ that can be employed there. These challenges include issues of attribution, wide-spread dual use of objects for military and civilian purposes, difficulties with identifying hostile intent and whether attacks with temporary and reversible effects (such as dazzling satellites through directed energy attacks, i.e., temporarily blinding an imaging satellite by using a laser to interfere with its sensor or jamming of GPS signals) would meet the threshold of prohibited force under jus contra bellum. As such, the use of force in outer space makes for an apt case study to demonstrate how the type framework can be applied to an emerging domain to analyse whether certain acts constitute an unlawful use of force or not. We will focus on a current counterspace capability that has already been demonstrated, namely, direct-ascent ASAT (DA-ASAT) tests.

DA-ASAT Tests

Due to their visibility, predictable paths, limited manoeuvrability, fragility and low defensibility, satellites are highly vulnerable to attack and other forms of interference.⁷⁵ The high speed of satellites (about 17,500 km/hr in low Earth orbit) also renders them vulnerable to destruction by collision with small objects on different orbits.⁷⁶ Forms of attack on satellites include kinetic attacks such as direct-ascent ASAT weapons (e.g. anti-ballistic missiles which can also kill satellites) and on-orbit ASAT weapons (e.g. a satellite releasing an object which will collide with another satellite). Several States, including the United States, Russia, China and India, have already developed counterspace capabilities, including anti-satellite weapons.⁷⁷ On 15 November 2021, Russia launched an unannounced DA-ASAT missile test to destroy one of its own defunct satellites. The destructive impact forced astronauts and cosmonauts aboard the International Space Station to seek shelter in their hardened Crew Dragon and Soyuz capsules from thousands of trackable pieces of space debris, many of which will remain in orbit for months or years.⁷⁸ In addition to the trackable space debris, there will be tens of thousands of untrackable but still lethal debris created that, because they are untracked, cannot be avoided through manoeuvres. This is not the first kinetic DA-ASAT test creating long-lasting debris: notoriously, China conducted such a test in 2007, blowing up one of its own weather satellites and creating several thousand trackable pieces of debris.⁷⁹ The United States conducted a kinetic DA-ASAT test in 2008, creating 400 pieces of trackable debris,⁸⁰ as did India in 2019, creating a similar amount of trackable debris.⁸¹

A major issue with kinetic ASAT weapons is the side effect of creating space debris, with even small pieces able to destroy other space objects due to the often high relative velocities of objects in orbit.⁸² Risks from space debris are increasing due to a rapidly changing orbital environment characterised by higher congestion including from abandoned rocket bodies and satellite mega-constellations.⁸³ In the worst case, space debris can trigger the Kessler syndrome, a collisional cascade that could make some orbits unsafe to access and use for decades. The clear dangers of space debris have led to calls for a treaty banning kinetic ASAT testing⁸⁴ and unilateral declarations by a growing number of States including the United States,⁸⁵ Canada,⁸⁶ Germany,⁸⁷ New Zealand,⁸⁸ the UK,⁸⁹ Japan⁹⁰ and Australia⁹¹ committing to refrain from such testing.

In the absence of physical effects on another State, the use by a State of a DA-ASAT weapon against its own satellite is not a prohibited use of force, because the contextual requirements are missing. But what if the DA-ASAT test creates debris which causes physical damage to or destruction of another State’s space object?⁹² We shall apply the type theory framework to assess this question. The scenario in question is the use of a DA-ASAT missile strike that targets and destroys a State’s own satellite, creating debris which permanently damages or destroys another State’s satellite.

Contextual Elements

Whether the contextual elements of article 2(4) of the UN Charter are met in this scenario primarily depends on whether the incident is regarded by States as taking place in their ‘international relations’. As argued in Chapter 4, the text of article 2(4) and its object and purpose do not exclude an interpretation that encompasses a use of force that is in ‘international relations’ outside the context of State damage, such as malicious destruction of parts of Antarctica, the Moon or other celestial bodies as terra nullius, if it is ‘inconsistent with the Purposes of the United Nations’. This is as yet untested in State practice. In any case, our case study is concerned with the creation of debris which damages or destroys another State’s satellite.

Whether such damage is considered to be in ‘international relations’ will be influenced by the perceived intent of the State conducting the DA-ASAT test and the degree of recklessness in carrying out the strike. Intent is discussed later in the chapter as an element of ‘use of force’. An assessment of whether the incident occurs in ‘international relations’ will of course also depend on the relations between the States concerned. Damage to another State’s satellite caused by debris generated by a DA-ASAT test is more likely to be perceived to be in ‘international relations’ if there is already a heightened state of tension between the two States – for example, between Russia and the United States. Alternatively, it could be considered that all such incidents are in ‘international relations’ because they take place in the context of the Outer Space Treaty and negatively affect the freedom for exploration and use by all States guaranteed in article I.

In addition to being in ‘international relations’, to meet the contextual elements of article 2(4) and fall within the scope of the prohibition, a use of force in space must also be ‘against the territorial integrity or political independence of any state, or in any other manner inconsistent with the Purposes of the United Nations’. States may not assert sovereignty over celestial bodies (article II OST). Nevertheless, State practice and subsequent agreement regarding the interpretation of the UN Charter confirm that uses of force against objects or persons with a certain nexus to a State may fall within the scope of article 2(4), for example, uses of force against private vessels and aircraft registered to another State.⁹³ Similar to flag ship jurisdiction, under article VIII of the OST, ‘[a] State Party to the Treaty on whose registry an object launched into outer space is carried shall retain jurisdiction and control over such object, and over any personnel thereof, while in outer space or on a celestial body’.⁹⁴ With respect to space objects, it is as yet unclear if registration would suffice for a use of force against the object to be considered ‘against the territorial integrity or political independence of any state, or in any other manner inconsistent with the Purposes of the United Nations’ or if a more specific nexus with the State is required. The function of the space object (military/civil vs commercial) will be relevant to this determination – an assessment that overlaps with the element of ‘force’ of effects (discussed later). Other factors that may be relevant to determining if the required nexus is met are the number of satellites struck⁹⁵ and the value of the satellite, financially or in terms of the importance of its functions to the State.⁹⁶

Elements of ‘Use of Force’

• Means: A DA-ASAT missile is a kinetic weapon and thus employs physical means.

• Effects: The direct physical effects of debris generated by a DA-ASAT test colliding with another State’s satellite could well be catastrophic damage to or destruction of the satellite due to the high relative velocity that would likely be involved.⁹⁷ An issue is whether this effect is sufficiently proximate to the ASAT test since it is a secondary effect. A factor which may come into play in this assessment is the known risk that debris generated by a DA-ASAT test will collide with other States’ space objects. For example, even an ASAT test carried out at low altitude in an effort to minimise long-lived debris, such as the test conducted by India in 2019, has ‘the potential to affect a busy, near-future orbital environment that includes at least four planned “mega-constellations” from different countries: SpaceX’s Starlink with 42,000 satellites and Amazon’s Kuiper with 3236 satellites, both from the United States; OneWeb with 7000 satellites from the United Kingdom; and Guo Wang’s StarNet with 12,992 satellites from China.’⁹⁸ If a collision of space debris from an ASAT test destroys another State’s satellite, there may be further serious effects. Damage to or destruction of a satellite may adversely affect critical military functions such as ‘ISR, meteorology, communications, PNT, and SSA [space situational awareness]’, which are of particular importance for co-ordinating forces in distant theatre conflicts.⁹⁹ The use of force in space could also have significant non-military effects. Disabling, damaging, or destroying such satellites, including through missile attacks, could have ‘wide-reaching consequences for civilians on earth’.¹⁰⁰ Canada’s submission to the UN Open-Ended Working Group on Reducing Space Threats (OEWG) in May 2022 stated that:

  Actions that disrupt or impair the delivery of critical space-based services, resulting in serious risks for the safety and security of people or property are irresponsible and could be perceived as a threat. For example, actions that disrupt a satellite’s ability to provide crucial information to the public, such as navigation information used by aircrafts to avoid collisions or data used by emergency responders to forecast and/or respond to major disasters. These effects and consequences are expected to increase as more terrestrial activities leverage space to deliver services.¹⁰¹

  Similarly, there are potential secondary physical effects of the destruction of a satellite from space debris generated by an ASAT test.

  Due to the high impact energies involved, debris from a kinetic ASAT test often ends up on highly eccentric orbits that cross multiple satellite ‘orbital shells’ twice per revolution. If just one piece of debris from such a test collides with a satellite and causes a major fragmentation event, this could lead to additional events affecting all States, which could include further fragmentations, satellite failures, or service disruptions.¹⁰²

It is not clear how far such physical and non-physical secondary effects are relevant to a determination of a use of force as the effects are not direct; there are intermediate steps between the forcible act (the DA-ASAT test) and such effects, namely, the creation of debris and the collision of that debris with a satellite. Even if these secondary effects are legally relevant to an assessment of ‘use of force’, establishing causation between a DA-ASAT test and these secondary effects may be challenging and will only ever be possible with regard to trackable debris (noting that non-trackable debris poses just as great a risk, especially because it exists in far greater numbers and total surface area).

• Gravity: As already noted,¹⁰³ the gravity threshold of a prohibited use of force is controversial. This is all the more relevant in outer space due to the range of intensity of uses of force which are possible in outer space, as well as the dual-use nature of many space objects which may entail significant secondary effects of an attack, as discussed earlier. In the 2019 Report of the UN Group of Governmental Experts on Further Practical Measures for the Prevention of an Arms Race in Outer Space (GGE), ‘[i]t was considered that threats exist on a continuum from low intensity, characterized by reversible and disruptive impacts, to high intensity, characterized by irreversible and destructive impacts’.¹⁰⁴ Damage or destruction to another State’s satellite by the creation of debris would fall into the highest level of intensity as assessed by the GGE. The gravity of the secondary effects (if legally relevant, as discussed earlier) will vary depending on the function of the damaged space object and could potentially be very high. The ICRC has noted the ‘potentially significant human cost for civilians on earth of the use of weapons in outer space’.¹⁰⁵

• Intent: As explained in Chapter 6, the text of article 2(4) and its travaux préparatoires do not indicate whether a ‘use of force’ must be motivated by a hostile intent or be intentional at all, in other words, whether mistaken or accidental uses of force also fall within the scope of the prohibition. However, emerging State practice gives early indications that only acts which deliberately cause damage to or interfere with space objects are likely to be perceived as a security threat and/or a use of force. Although none of the international efforts to define a ‘use of force’ in outer space have achieved consensus so far, it is notable that the draft treaty sponsored by Russia and China on the Prevention of the Placement of Weapons in Outer Space, the Threat or Use of Force against Outer Space Objects (PPWT) in 2008,¹⁰⁶ the revised definition in the 2014 Draft PPWT¹⁰⁷ and the 2019 Report of the GGE all share reference to intentional acts.¹⁰⁸ The US criticism of the definition of ‘use of force’ in the 2008 draft PPWT notably did not criticise the requirement that the action be ‘hostile’.¹⁰⁹ This approach is also supported by Canada’s submission to the OEWG in May 2022, which distinguishes between irresponsible behaviours, such as actions leading to damage to the space environment (e.g. debris creation), and actions which are security threats, such as ‘deliberately causing non-consensual interference’ to space systems.¹¹⁰ It therefore seems likely that States would consider intent as an essential element of a ‘use of force’ in outer space, whereas accidental, mistaken or recklessly caused damage will be perceived as irresponsible or unsafe behaviours.

The difficulty is that a deliberate or hostile intent is difficult to discern in outer space. It may be difficult or impossible to verify if acts which cause damage to or endanger space objects are intentional, such as collision of space objects and the creation of space debris. Since the risks of space debris creation (and collision) from DA-ASAT tests are known, such tests are at the very least reckless. One may well question whether deliberately ignoring the warnings of one’s own scientists about the certainty of debris creation constitutes negligence or wilful blindness amounting to a deliberate act. However, in the absence of other evidence in a particular case, a DA-ASAT test is not likely to fulfil the element of an intention to damage or destroy other States’ space objects.

Conclusion

The elements of ‘use of force’ that are present are thus physical means, physical effects and high gravity. The element which is missing in this hypothetical scenario is a hostile or deliberate intent. However, given the known dangers of space debris, deliberately creating debris which causes damage to another State’s space object is unlikely to be seen as a mere accident or mistake, and at the very least as reckless. Does this combination of elements suffice to reach the threshold of a prohibited ‘use of force’? Perhaps not. But if some of the elements are more heavily weighted in the scenario, such as secondary effects with a high gravity (e.g. if a satellite that carries out key military or civilian functions is destroyed by the debris) and the conduct evinces a particularly reckless or potentially hostile intent (e.g. the ASAT test is unannounced and conducted at high altitude and there are pre-existing tensions between the State conducting the ASAT test and the State whose satellite is destroyed by the debris), then all of these elements in combination could meet the threshold. Thus, in certain circumstances, the creation of debris by a State conducting a direct-ascent ASAT test which then damages or destroys the space object of another State could constitute a prohibited ‘use of force’ in violation of article 2(4) of the UN Charter and customary international law. Due to the rapidly escalating militarisation of outer space, the grave and widespread potential effects of uses of force in this domain and uncertainty over how to define a prohibited ‘use of force’ in outer space (particularly with respect to non-kinetic attacks and attacks with temporary effects), the application of type theory to the use of force in outer space acquires particular salience and demonstrates the potential utility of this framework.

Reflections

A key observation arising from the case studies in this chapter is the importance of the contextual element of ‘international relations’ for an act to fall within the scope of article 2(4) of the UN Charter and the implications this has for the significance of certain elements of a ‘use of force’, namely, object/target, gravity and intention. These three elements are relevant to the characterisation of an act as a ‘use of force’ and also contribute towards an assessment of whether the act meets the contextual requirement that the ‘use of force’ takes place in ‘international relations’. This explains why the element of a hostile or coercive intent is present in each of the unlawful uses of force examined in this chapter; in the absence of a hostile or coercive intent, it is difficult to show that the contextual element of international relations is met and that the act falls within the scope of article 2(4). The relationship between intention and international relations is mutual, as an overtly hostile or coercive intent increases the likelihood that the act is in international relations and heightened tensions in the international relations of the two States concerned may signal a hostile intent behind a forcible act. As the examples in this chapter show, a hostile or coercive intention is not only relevant to the contextual element of ‘international relations’ but also to the determination of whether the act is a ‘use of force’.

Similarly, the object/target of a forcible act and its gravity may indicate whether the act is in ‘international relations’ as well as being elements to weigh in assessing whether it is a ‘use of force’. Unlike intention, the object or target of a use of force is not necessarily decisive, as a use of force can still be in international relations without a strong nexus between the target and another State (e.g. in the Skripal incident discussed earlier in this chapter). International relations must definitely be present as a contextual element, whereas the object/target of the forcible act, its gravity and intention may be balanced with the other elements of means and effects to determine if it is a ‘use of force’.

The examples analysed in this chapter illustrate how type theory can be applied to particular incidents to determine whether they are an unlawful ‘use of force’ in violation of article 2(4) of the UN Charter and customary international law. The utility of this approach is that it provides a framework for a systematic analysis of an incident to be able to assess whether it violates the prohibition of the use of force or not. The framework is helpful in breaking down the analysis of specific forcible incidents to be able to identify and weigh each element. Type theory is also useful for seeing how contextual elements shape whether an act is a prohibited use of force. This enables a meaningful discussion and debate about whether and why a particular incident is or is not a prohibited ‘use of force’. In particular, the type theory framework is useful in borderline and novel cases, such as when the forcible act is at the low end of the gravity spectrum, there is a potentially applicable parallel legal framework (e.g. law enforcement), a kinetic weapon is not used (e.g. cyber operations) and in emerging military domains (e.g. outer space).