The development of automatic dead reckoning navigation instruments owes its main impetus to the needs of the airman during the second world war. It was foreseen that manual plotting would not be adequate, for example, in bomber operations where frequent changes of course are desirable and speed and height are not always accurately maintained, and it was realized that automatic computing of position would provide improved reliability and accuracy. The instruments developed have been described elsewhere, and this paper outlines their early history rather than details of their design. It also indicates some future possibilities.

Existing instruments. The main instrumental aids to dead reckoning navigation which came into use during the 1939–45 war were the distant-reading gyro-magnetic compass, the air mileage unit and the air position indicator. From them evolved the ground position indicator and the wind finding attachment, both used for special purposes towards the end of the war.

Early in the 1930's Captain L. C. Bygrave constructed an experimental instrument which undoubtedly influenced later developments. This instrument was to be fed by a gyro-magnetic compass with heading and from an air log with air distance; on it could be set wind speed and direction and aircraft speed and course. The instrument showed departure in miles north-south and east-west.