B-17 Upper Machine Gun Turret (Type A-1A) By This turret was one of the first fully-powered machine gun turret designs used to equip American aircraft and was used initially on the B-17E Flying Fortress. It is operated by an electro-hydraulic system, which powers both elevation and traverse of the turret's two .50-cal. M2 Browning machine guns, and has a rate of fire of 1,400-1,600 rounds per minute. Turrets of this and later types gradually replaced manually-operated machine guns introduced for bomber defense during the First World War, and so made the bomber and more formidable opponent to attacking fighters. This turret was manufactured by the Emerson Manufacturing Co. to a Sperry Gyroscope Co. design and was donated to the museum by the Hobart Corp. of Troy, Ohio. Click here to return to the World War II Gallery.