The History of Air Navigation Group commissioned the author to provide a brief account of airborne DR development by discussing both the methods and the equipment used in the air. This second and final part covers the period after 1940 which saw the automation of DR techniques from the Air Position Indicator of the 1940s to the Flight Management Systems in current use.

The History of Air Navigation Group commissioned the author to provide a brief account of airborne DR development by discussing both the methods and the equipment used in the air. This first part covers the period before 1940. The split is arbitrary, although it is obvious from a British perspective that military events around that date had a major impact on the pace of navigation development. However, it is equally obvious that airborne DR developed alongside a worldwide technical and intellectual revolution. This aspect of the story is abstract and involves some conjecture, so the paper takes it for granted and concentrates instead on practical matters. Accounts of air navigators' experiences as well as material on DR theory and descriptions of DR equipment in navigation manuals, journals and various surviving research documents have been used as the source material.

According to comprehensive theories of navigation, animals navigate by using two complementary strategies: (1) dead reckoning informs the subject in a continuous manner on its actual location with respect to an Earthbound or absolute coordinate system; while (2) long-term associations between particular landmarks and specific locations allow the animal to find its way within a familiar environment. If the subject structures familiar space as a system of interconnected places – the so-called ‘cognitive map’ – it may know through dead reckoning where it is located on its map and relate its route-based expectations to the actually perceived scenario of local cues.

This paper is based on the Eva G. R. Taylor lecture given by the author at the Royal Geographical Society on 28 November 1990. The precise landfall of Columbus in the New World has been the subject of discussion for many years owing to various interpretations of the information given by copies of his log and his own statement that his San Salvador lay about 28° north. The twofold aims of the author's 1989 voyage were: first, to experiment with fifteenth-century methods and instruments to find out by practical experimentation how accurate the navigation at the time might have been and so cast light on this 4° error in latitude; and secondly, to follow the navigation information given by Columbus as closely as possible to assess the effect of the currents on his dead reckoning as clues as to his landfall.