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"Filling of recuperator cylinder on M-4 aircraft cannon installed in Lockheed YP-38, P-38, P-38D, Bell YP-39, P-39C and P-39D airplanes." Source: War Dept. OCAC Technical Order ...

Airplanes - Lockheed P 38 - Armament; War Dept. - Technical Order 01-1-40. Third Series; Airplanes - Lockheed P 38 D - Armament; Airplanes - Bell P 39 - Armament; Airplanes - Bell P 39 C - Armament; ...