Sextant, Aircraft Periscopic, RAF Mk II, Ref No 6B/2838 KC-135 See image of spec sheet

See image of spec sheet

It has a screw-type heeling compensator

Here is a very interesting document

or very similar to

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

Sextant, Aircraft Periscopic, RAF Mk II, Ref No 6B/2838 KC-135 See image of spec sheetHere 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