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's features included remote control guns, pressurized crew areas connected by a long tube over the bomb bays, and a separate pressurized area for the tail gunner that could only be left during unpressurized flight. The B-29 used the high-speed Boeing 117 airfoil, and its larger Fowler flaps added to the wing area as they increased lift. Modifications led to the B-29D, upgraded to the B-50, and the RB-29 photo reconnaissance aircraft. After the war, B-29s were adapted for several functions, including in-flight refueling, anti-submarine patrol, weather reconnaissance and rescue duty.