Air Position Indicator System Computer 12580-3-B & Manual T.O. 5N-3-1-31
The Air Position Indicator System was an advanced navigational system introduced during WWII in later versions of the Boeing B-29 Superfortress Bomber by the US Army Air Force, including the Enola Gay (see API on navigator's panel). This electro-mechanical system computed positions based on a series of dead reckoning inputs.
The system maintained a continuous indication of the latitude and the longitude of the air position at any instant, as well as the mileage flown. By plotting this information on a chart and by applying the wind vector, representing the direction and distance the air has moved during the elapsed time, the navigator obtains the ground position of the aircraft. The system consisted of 4 components (computer, pump, controller, amplifier) plus an optional right-angle drive. It was operated in conjunction with the Bendix Gyro Flux Gate compass system or a remote indicating magnetic compass.
This listing includes the Computer (part number 12580-3) and the Handbook of Operation and Service Instructions T.O. 5N-3-1-31 revised August 1950. The Air Position Indicator Computer was installed in the instrument panel of the navigator, although we have seen at least one photo of it installed on the main flight panel of an unknown aircraft in a 1945 publication.
While we don't know the year of manufacture, this API Computer has a modification date of 1955 and a service date of 1965. It is in exceptional condition given its age. Measures 4 inches diameter and ~11 inches deep.