The FN5 was designed to replace the original Barnes Wallis turrets used in the Wellington bomber. It was later used as the nose turret of the Manchester, Stirling and Lancaster bombers, making it the most numerous British gun turret of the Second World War. In all, over 22,000 FN5 turrets were produced.
The FN5 carried two 0.303in Browning Mk II machine guns, with 1000 rounds per gun. The two guns were fed from ammunition boxes fitted on either side of the gunner and used as arm rests. Oxygen, intercom and electrical services were brought into the turret, together with the hydraulic feed pipes, through a rotating service joint in the top of the cupola.
An engine-driven hydraulic pump provided power to rotate the turret, elevate the guns and power the firing mechanism. The turret was controlled by two separate control handles, mounted on each side of the turret frame. The turret could be turned by hand by the gunner in an emergency.
The gunner’s parachute was attached to the fuselage just outside the turret. If he needed to abandon ship, he had to turn the turret to point forwards, open the door, retrieve his parachute, close the door, rotate the turret until it was fully turned to one side, then open the door and fall backwards out of the turret. The turret could also be rotated manually from inside the aircraft, to rescue a trapped or wounded gunner.
The FN5 turret on display was fitted to the nose of a Lancaster bomber.