German U-Boat Kreiselsextansen KS-3D 1945 (SEXT15)

This is a WWII-era nautical sextant used on German submarines. 

According to collector George Fulford's notes:

I paid through the nose for this rarity in early 2007. I’d been looking for one forever and when it came up on EBay I competed with bidders from all over the world, and I was lucky and glad I won because I doubt another will ever come up again.

Essentially, this is the same as the preceding Kriegsmarine aviator’s sextant. Except this one was modified specifically for U boats that had found out the hard way they no longer had the luxury of using their traditional sextants due to enemy aircraft and warship harassment. To speed up the shot they could reduce the averaging to 30 seconds, and most significantly they incorporated a gyro device for the artificial horizon. The idea was to be able to use this via the periscope. The January 1945 date on this copy suggests it never saw action, though it could have got as far as a U boat navigator’s desk in port as Germany still had nearly 100 operational U boats at the end of the war. For more on this, go to the U Boat Web. There isn’t a more comprehensive and fascinating site on the web. Period.