Turrets and Mountings
Originally, most bombers defensive armaments were single hand-operated machine guns pivoting on a mounting attached to the structure of the plane. The main disadvantages being that it was always difficult to turn the gun into a 200mph slipstream and therefore the field of fire was severely limited. The next development was to give the gunner a rotatable mounting so that he coult pivot toward the enemy. The slipstream problem was overcome by installing powered gun turrets which traversed the turret and the gun mounting ring, leaving the gunner free to control movements in azimuth and elevation by hand. Powered turrets soon became very sophisticated. Guns could be moved at 50° per second and gunners could literally sign their names on a card if they placed a pencil in the gun barrel. guns of a B-17 were electically fired and electrically fed with ammunition. The defensive capabilities of all erly bombers against attack from underneath were usually minimal and the only really seccessful manned turret was the US Sperry ball type that fitted to the B-17 and the B-24. It was unique in that it was electro-hydraulically powered and the gunner lay on his back to operate it.
At the beginning of the war, gunsights were simple ring and bead type in which a gunner had to maintain a constant eye base. Accuracy depended on the gunner´s skill in calculating deflactions (the swerving path of fire towards the target) but it was still extremely difficult to hit a moving object. These were eventually secceeded by the reflector sight; essentially an optical sight that left the gunner freedom to move his head to an from the sight without creating an error in deflection. The gunner had only the target to watch with the reticule in the optical viewer superimposed on it. By the end of war most bombers either had gyroscopically predicting sights that gave very accurate deflectionshooting, regardless of the relative position of target and gun, or compensating sights that took account of the forward speed of the aircraft and related if the trail and motion of enemy fighter.