The Boeing 377 Stratocruiser was a large long-range airliner developed from the C-97 Stratofreighter military transport, itself a derivative of the B-29 Superfortress.

[3] Its design was advanced for its day; its relatively innovative features (though neither completely new) included two passenger decks and a pressurized cabin.

A 377 was also converted into the Aero Spacelines Pregnant Guppy by John M. Conroy for NASA’s Gemini space program.

William Allen, who had become president of the Boeing Company in September 1945, sought to introduce a new civilian aircraft to replace reduced military production after World War II.

[8] It was one of only a few double deck airliners ever built for commercial use, another being its French contemporary, the Breguet Deux-Ponts, as well as later models, the 747 and the Airbus A380.

[9] Adoption of the Stratocruiser got a boost from the US government, with a controversial incentive package offered to Northwest Orient Airlines for its purchase.

Its components were unusually generous mail contracts offered to Northwest for opening new routes to Hawaii and points in the western Pacific region that they were invited to apply for, and a Reconstruction Finance Corporation loan earmarked for the purchase of a fleet of Stratocruisers.

On this delivery flight, Boeing engineer Wellwood Beall accompanied the final 377 to England, and returned with news of the de Havilland Comet, the first jet airliner, and its appeal.

[15] For a short time, Pan Am 377s flew to Beirut, Lebanon, but after 1954, no 377 was scheduled east of Europe or west of Singapore.

[17] In 1956, Pan Am 377s flew from Los Angeles and San Francisco to Sydney with stops at Honolulu, Canton Island and Suva (via Nadi Airport in Fiji).

[19] Within six years of first delivery, the Stratocruiser had carried 3,199,219 passengers; it had completed 3,597 transcontinental flights, and 27,678 transatlantic crossings, and went between the United States and South America 822 times.

By 1954, the lack of spares and the inability to cross-train their Douglas crews with the type relegated their Stratocruisers primarily to their Hawaii route, where they faced stiff competition from Pan American and Northwest.

The longest (by distance) 377 nonstop flights were made by Pan Am from Tokyo to Honolulu during four winter seasons beginning in 1952–1953.

High operating costs (notably the fuel consumption and maintenance of the Wasp Major engines) led to rapid abandonment of the 377 with the onset of the jet era.

The hulks were stored at Oakland International Airport through the 1960s and cannibalized for parts, contributing some to the Aero Spacelines Guppies.

The aircraft type also experienced a significantly high rate of in-flight emergencies related to engine and propeller failure, resulting in Airworthiness Directives.

Directives were issued in 1950, 1955, and 1958 regarding enhanced maintenance and fault detection, in-flight vibration monitoring, and propeller replacement.

A June 1957 overspeed incident occurred on Romance of the Skies, after the compliance date of the Directive and less than six months before its fatal accident of November 8, 1957.