Master Indicator, Type N-1 Compass System plus Service Manual
This is a Master Indicator used in the N-1 Compass System by aircraft of the US Air Force during the 1950's and into the 1960's. The N-1 system is a remote-indicating, gyro-stabilized compass system designed for use in all latitudes, which is what made it unique at the time. The N-1 system was commonly used in early models of the US Air Force bomber B-52 Stratofortress, transport C-130 Hercules, and air tanker KC-135. It was installed at the navigators station. See an illustration of the N-1 Indicator from the KC-135 Flight Manual dated 1966.
From K.Greenaway, Forum, Journal of Navigation, 1990.
...The Kearfott N1, as it was known in the United States and Canada, was the premier heading reference system for high-latitude flying in North America throughout the early nineteen fifties. Its origins began in 1945 through a request by the USAAF for a directional gyroscope specifically for polar flying, followed by discussions between Kearfott engineers and members of the USAF/RCAF LF Loran Flight Test Unit involved in polar flying out of Edmonton, Canada, between 1946 and 1950. Kearfott began
producing the N1 in quantity in late 1950. It was the forerunner of the Bendix Polar Path and Sperry CL 11...
The N1 system departed in principle from compasses such as the Gyrosyn in that the gyro always remained 'free'; only the indications were slaved. It combined several features of the Magnesyn G2 Compass used by the US Navy and the Pioneer Fluxgate. In addition to its reliability, features of the Kearfott system most popular with polar fliers of the time were:
(i) The ability to disconnect the magnetic slaving signals of the C2 Fluxvalve.
(ii) The provision of a controller to precess the heading indication at sine lat. x 1 g° per hour to correct for apparent drift due to the Earth's rotation.
(iii) The specification of 1° per hour random error when in the directional gyro mode, and seldom reached, was a pleasant experience for aircrews conditioned to gyros of World War II vintage.
There is an excellent video USAF training film for the system at YouTube, here: N-1 Compass System Training Video