The tail gun of a B-17 Flying Fortress. Image stamped on reverse: 'Keystone Press.' [stamp], 'Passed for publication 9 Jul 1943.' [stamp] and '273689.' [censor no.] Printed caption on reverse: 'FLYING FORTRESSES ARE POWERFULLY ARMED. The feature of the defensive equipment of Flying Fortresses (also of Thunderbolts) is the calibre. 50 Machine Gun. Format guns of Flying Fortresses have an average of 12 and a half machine guns. 50 calibre per plane. The length of the cartridge is [illegible] Each plane carries not less than 6250 pounds weighing 1875 pounds of ammunition. The entire defensive equipment of a Flying Fortress is more than 5700 lbs or between 7 and 8% of the gross weight of the aircraft. The extremely heavy defense of the Flying Fortrs has enabled them to fight their way through in face of the most intensive fighter opposition aerial warfare has ever seen. Keystone photo shows: Rear gun of A Flying Fortress.'