The B-17E was the first mass-produced model of the B-17 and literally bristled with armament. It was several tons heavier than the Model 299 prototype and included .50-caliber machine guns in a two-gun power turret on top of the fuselage just behind the pilot's cabin; a two-gun, manually operated Stinger turret in the tail; and a power turret on the bottom of the fuselage behind the wing. A .30-caliber gun remained in the nose, and two .50-caliber guns were on each side.