Sextant, Aircraft Periscopic, MS28011-5, with Case, for Display, Parts, or Repair
This is a Cold War-era Periscopic Aircraft Sextant and Case, as used by navigators in aircraft of the US Air Force such as B-36 Peacemaker, B-47 Stratojet, B-50 Superfortress, B-52 Stratofortress, C-130 Hercules, and of the US Navy such as the P2V Neptune and others. This example has a serial # prefix of AF-53, manufactured under a USAF purchase order issued in 1953.
The periscopic sextant was used by navigators to fix and track the position of the aircraft in flight, usually by nighttime celestial (star) readings, but also by the position of the sun in daylight. The periscope of the sextant would be inserted through a shutter mount in the top of the cabin to obtain a reading. By viewing the spirit bubble through the eyepiece, the navigator levels the sextant to ensure accurate celestial readings. The sextant also has a timed recording device by which the navigator records readings while in flight.
The sextant is in reasonable cosmetic condition given its age. It was last used by the Aerospace Guidance and Metrology Center in Newark OH and last serviced in 1984. The unit requires calibration as we are unable to adjust it to view the sky in the viewfinder. We have no way of testing the sextant for correct operation, but all knobs turn and the timer runs. The case is clearly experienced and was painted at some time. The rubber cavity for the sextant body has deteriorated with age, requiring an added plastic barrier to protect the sextant from the sticky rubber, see photo. It contains some spare lamps as well. The case measures ~11 inches by ~8 inches by ~18 inches, which gives one a sense of the size of the instrument, and the entire kit weighs 21 lbs.
Here is a link to transcribed sextant instructions including this periscopic sextant.