Early models of the B-36 Peacemaker intercontinental bomber relied on concentrated fire from multiple gun turrets for protection from fighters. This concept had been used in World War II bombers, and the B-36 was the last U.S. bomber to employ massed gun turrets for defense.
Early B-36s had six turrets like the General Electric model on display, which mounts two M24 20mm cannon. Separate gunners operated each turret by remote control in individual sighting stations. When not in use, turrets retracted into the Peacemaker's fuselage to cut wind resistance and save fuel, thus preserving the bomber's great range. A turret in the tail was radar-aimed and nonretractable. The nose also had a nonretractable turret.
Reliability and aiming problems made the gun system troublesome. Finally the B-36 "Featherweight program" removed the heavy guns and protected the aircraft instead with speed, maneuverability and altitude. Only the tail turret remained for protection from the rear. All B-36s eventually were converted to Featherweights.