Gunsight, K-13 Compensating Sight TBM Avenger Used in post-WWII 4 engine

Used in post-WWII 4 engine aircraft such as B-50

but the markings on the compass card are clear and precise

The case has compartments which suggest that it might have once contained additional lenses

Used for sighting 3"/50 guns

According to Designation-Systems

Gunsight, K-13 Compensating Sight TBM Avenger Used in post-WWII 4 engineThe K 13 Compensating Gunsight, made by Sperry, is a electrically powered gunsight designed to compensate for altitude and airspeed. Typically mounted on the rear housing of a 50 cal machine gun from a side waist gun position in the aircraft. Used in Boeing B 17 Flying Fortress and Consolidated B 24 Liberator bombers during WW2. It was a late war innovation that used the aircraft altitude and speed with the direct correlation of where the weapon was