The Boeing 377 Stratocruiser was the airliner version of the 367 Boeing Stratofreighter, which in turn was the transport version of B-50 Superfortress. It first flew on July 8, 1947.
Despite serious design flaws and a marginal service record, the Stratocruiser was one of the great post-war propeller airliners. Extremely complex and expensive, only 56 were built. It continued in mainline service until 1960, by then it had been made obsolete by the coming of the 707 and other first generation jetliners. The 377 was the flagship of the Pan Am and BOAC fleets from delivery in 1949 until the arrival of the 707 and de Havilland Comet respectively. Its spiral staircase, which led to a lower-deck lounge, inspired the one on the 747. It was one of the few airliners with a double-decker seating arrangement (another was the French Breguet Deux Ponts) until the 747, however some airlines had lower-level lounges on their L-1011 Tristar aircraft.