The sign accompanying the turret. It reads
The A-9 turret was designed for and used on the North American B-25J Mitchell medium bomber.
Located on top of the fuselage just behind the cockpit, it contained two
Browning .50 caliber machine guns each
firing up to 550 rounds per minute. A type N-6A gunsight was mounted between
the guns. Ammunition boxes located at the
front contained 400 rounds for each gun.
The turret was powered by a one-half horsepower electric motor. It could
rotate a full 360 degrees at 33 degrees per second and the guns could be
elevated from horizontal up to 90 degrees. An interrupter system prevented the
guns from being fired when pointed at any part of the airplane or propellers.
The gunner sat on a bicycle seat attached
to the center pedestal with his feet resting on adjustable footrests.