Sextant, Aircraft Periscopic, RAF Mk II, Ref No 6B/2838 KC-135 It has a screw-type heeling

It has a screw-type heeling compensator

2 inch by 7-inch wide negatives in 120-type film

This is an original WWII-era training booklet published by the US Navy's Aviation Training Division in 1942

or very similar to

See image of spec sheet

Sextant, Aircraft Periscopic, RAF Mk II, Ref No 6B/2838 KC-135 It has a screw-type heelingHere is an original aircraft Periscopic Sextant Mk II as used in aircraft of the British Royal Air Force, in its original carrying case. The periscopic sextant was used in aircraft with a pressurized cabin, whereas the 'periscope' was inserted through a shutter mounted in the ceiling of the aircraft. This provided an unobstructed view of the sky for celestial navigation without compromising the pressurization of the crew cabin. The serial number of