Boeing submitted the Model 345 design for a long-range heavy bomber to the Army in 1939, before the United States entered World War II. In May 1940 Boeing received an order for two flying prototypes and one static loads test aircraft, designated the XB-29. The resulting B-29 Superfortress 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.