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

but also on the US Army Air Corps' UC-43 Beech Staggerwing (see photo from flight manual dated 1944)

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