The Boeing 377 Stratocruiser was born from war provenance. After Boeing built 2,766 B-29 Superfortress bombers during World War II, the company adapted the bomber's wing and fuselage structure into a civilian airliner, powered by four Pratt & Whitney R-4360 engines. The result was the Stratocruiser, with its distinctive double-bubble fuselage—two pressurized cylinders stacked one atop the other, creating enough interior volume for a lower-deck lounge complete with a cocktail bar and sleeping berths. The prototype first flew on July 8, 1947, and Pan American World Airways inaugurated service on April 1, 1949. The Stratocruiser's most famous route was the SFO-Honolulu inaugural, a roughly 8.5-hour flight that redefined transpacific luxury travel. Only 56 were built—Boeing lost money on every one—but the type established the standard for post-war long-range comfort. The upper deck seated 55 to 100 passengers, while the lower deck lounge offered a space no rival could match. By the late 1950s, the jet age had rendered the piston-powered Stratocruiser obsolete, but its legacy of passenger comfort influenced every wide-body design that followed.