WW2 AMERICAN ARMY AIR FORCE K-13 COMPENSATING GUNSIGHT MADE BY SPERRY, with manufacturer’s plate on the side reading: “Sperry Gyroscope Co., Inc., Brooklyn, N.Y., K-13 Compensating Sight, Part 659060, Ser. 29176, Cont. AC 3571.” This is a pneumatically-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 pointed to calculate the reticle. The aircraft altitude and speed were programmed on the rear of the sight. The correlation was determined by drive lines that connected the K-13 Sight to the K-7 Mount. In fine condition.