Boeing submitted the prototype for the B-29 long-range heavy bomber to the Army in 1939, before the United States entered World War II. The B-29 had many new features, including guns that could be fired by remote control. The crew areas were pressurized and connected by a long tube over the bomb bays. The tail gunner had a separate pressurized area that could only be left during unpressurized flight. The B-29 was also the heaviest production plane because of increases in range, bomb load and defensive requirements.