Aircraft Bubble Sextant, Japan (SEXT39)
This is a WWII-era aeronautical sextant from Japan.
According to collector George Fulford's notes:
The Japanese snitched a copy of the Army Air Corps A-8, of pre-WW2 vintage, and secretly made copies for their own use as they did not have anything of their own: and this is it. Unfortunately for them they should have waited for the A-8A, which had an averaging devise, crucial for accurate air celestial navigation that this one does not. I’m only superficially aware of the A-8 but comparing it with this Japanese copy I feel a weight difference and the bubble container is far smaller than ours, which can be significant, for the liquid in all the earlier sextants had a nasty proclivity to leak out which could be alleviated by having a larger reservoir.