Super rare, super cool set of great optics, WW2 U.S. Navy Ships Mark 91 6 x 50 Submarine Torpedo Targeting Binoculars, made by Bausch & Lomb Optical Co. These would have been mounted on the Submarine conning tower and remained on the bridge when the submarine dived hence the spectacular engineering and unusual stainless steel composition, which although a very scarce and expensive commodity in WW2, was used to combat the effects of sea water and the enormous pressures.

Hans Seeger ‘Fernglaser und Fernrohne’ pg390-392."U.S. Navy, Bu of Ordn./Telescope'/Mark 91 Mod 0 / Wt. 40 Ser No. 442 / Bausch & Lomb Optical Co." Castings have individual serial numbers. Inter pupillary adjustment by double-ended screw at objective end; objective covers with dark glass filters flip up. Fixed Focus; simple cross-hairs in right-hand optics. Magnification, not specified...

This type of binocular was mounted permanently on submarine conning tower bridges and made to withstand undersea pressures.”