Forgotten Firsts — Boeing 377 Stratocruiser

Suren Ratwatte


The most famous bomber of the Second World War is almost certainly the Boeing B-29 Superfortress, which has the dubious distinction of being the only atomic weapons delivery system used in war. The USAAF (United States Army Air Forces) B-29 with ‘tail number’ 44–86292 and dubbed Enola Gay, after pilot Colonel Paul Tibbets’s mother, will forever be remembered as the airplane that bombed Hiroshima, Japan, thus launching the ‘Atomic Age’ on August 6th 1945 — exactly 75 years ago.

B-29 Enola Gay — picture credit Britannica

The B-29 was the culmination of many years’ development by Boeing of heavy, long-range bomber aircraft. With its pressurized fuselage, tricycle landing gear and computer-controlled guns, the Superfortress was an advanced aircraft for its time; its successful design ensuring that it remained in service for almost 20 years, eventually being replaced by jet bombers such as Boeing’s own B-47 Stratojet and B-52 Stratofortress.

More than 3,900 B-29s were built, with the USSR producing 800-plus examples named the Tupolev Tu-4, after Soviet scientists reverse-engineered USAAF airplanes that had diverted to Vladivostok. Britain’s Royal Air Force also operated a version named the Boeing Washington, until 1954.

A transport version of the B-29 for the US military, designated the YC-97 Stratofreighter, with two B-29 fuselages placed on top of each other in an inverted figure-8 or ‘double-bubble’ formation, was already under development in 1944. (The name is a reference to the aircraft’s ability to cruise in the stratosphere, over 10km above the earth’s surface.) Concurrent with the prototype XC-97’s first flight on November 9, 1944, Boeing announced the launch of a commercial passenger version based on the B-29 design, to be known as the Model 377 Stratocruiser.


The war in the Pacific theater came to an abrupt end in 1945 with the destruction of Hiroshima and Nagasaki by atomic bombs dropped from B-29s. Soon afterward, Juan Trippe’s Pan American Airways, which had a long pre-war relationship with Boeing and its Type 314 Clipper flying boats, placed an order (the most expensive at that time) for 20 Model 377 Stratocruisers.

Pan Am Stratocruiser — picture credit Pintrest

The Stratocruiser shared the ‘double-bubble’ fuselage of the YC-97 and C-97, with passenger seats located on the ‘upper deck’ and the lower deck comprising a lounge, and cargo and baggage compartments. As the world’s first ‘double-decker’ civil aircraft, Boeing’s Model 377 Stratocruiser deserves its place in history.

The only other twin-deck propeller-driven aircraft were Bréguet Aviation’s family of Br.761/763/765 French-built transports. Informally called the Deux-Ponts (French for double-decker), only 20 examples of that ungainly type were produced, remaining in service with Air France and the French Air Force (Armée de l’Air Française) from 1953 to 1971.

Bréguet 763 — picture credit Manteufel

Operational history

A total of 56 Model 377 Stratocruiser airliners were originally ordered and operated by Pan American, American Overseas Airlines, United Air Lines, BOAC (British Overseas Airways Corporation), and Northwest Orient Airlines (NWA).

Fittingly, in view of the airline’s legendary trans-Pacific heritage, Pan American operated the inaugural Stratocruiser flight from San Francisco to Honolulu in April 1949. By the end of that year Pan Am, BOAC and American Overseas Airlines (which later merged with Pan Am) were flying the Stratocruiser on trans-Atlantic routes between New York and London, while Northwest Orient Airlines used it on domestic US routes including to Honolulu. United Air Lines operated the Model 377 briefly, but sold their aircraft to BOAC who needed extra capacity while its de Havilland Comet 1 jetliners were grounded following a spate of disasters involving the latter type.

The 377s, especially those operated by BOAC and Pan Am, were luxurious with opulent first class cabins and considerable cargo capacity. The 11ft (3.35m)-diameter fuselage and 6,600ft³ (187m³) of interior space distinguished the type as the largest passenger aircraft of its era. Powered by four Pratt & Whitney R-4360 Wasp Major radial engines, each with its 28 cylinders arranged in four rows of seven in spiral formation to maximize cooling at the rear of the engine, the Stratocruiser was a capable and fast machine. But it suffered from persistent maintenance issues relating to its complex power-plants and constant-speed propellers.

Pan Am’s luxurious interior and the 377s unique features — picture credit Pintrest

The main competitors to the Boeing 377 Stratocruiser were Lockheed’s Constellation series and Douglas Aircraft Company’s more utilitarian DC-4 and DC-6. The Boeing machine was also relatively expensive compared to its rival types. BOAC was the principal operator outside the USA, using the Stratocruiser on its prestigious ‘Monarch’ luxury service between London and New York.

During the Stratocruiser’s heyday, ten examples of the type were destroyed in accidents, only three of which were non-fatal. Three of the hull losses are known to have resulted from ditching at sea. The first by Pan Am’s Clipper United States, registered N1032V, on March 26, 1955, when the no. 3 engine and propeller tore away from the wing, forcing the crew to set the airplane down in the Pacific Ocean off the coast of Oregon. After staying afloat for 20 minutes the aircraft sank, causing four of the 23 occupants to lose their lives.

On April 2, 1956, engine failure on NWA’s Stratocruiser Tokyo (N74608) caused a ditching on Puget Sound, with the loss of five of the 38 ‘souls’ on board.

A second ditching of a Pan Am aircraft (Clipper Sovereign of the Skies; N90943), in the Pacific Ocean on October 16, 1956, had a happier ending, with all 31 occupants being rescued by the US Coast Guard.

With the introduction of Britain’s new, improved Comet 4, and Boeing’s 707 entering service, the 377 Stratocruiser was gradually withdrawn. BOAC operated its last service in 1959 and NWA a year later.

Later applications

But long after its mainstream airline career ended (a few second-tier US and Latin American airlines operated preowned 377s for a few more years), the Stratocruiser’s sound design saw the type continuing to serve well in various military and commercial applications. Most notable was the KC-97 Stratofreighter, a strategic aerial refueling tanker based on the C-97 Stratofreighter. A total of 811 examples of the KC-97 were built (in addition to 77 of the C-97), the majority for the US Air Force, with smaller numbers operated by the Israeli Air Force (IAF) and the Spanish Air Force (Ejército del Aire). Some of the IAF aircraft were modified and designated Anak (Hebrew for ‘giant’), for a variety of purposes including aerial refueling and as electronic warfare platforms. Earlier, the IAF had acquired five former Pan Am 377s and fitted them with swing tails and clam-shell doors to facilitate loading and unloading of bulky cargoes.

A7 Corsairs refueling from a KC-97 — picture credit Wikipedia

Aero Spacelines in the USA converted a few C-97s into large freighters by adding an extended upper fuselage which accentuated the double-bubble look of the original. They were primarily built for NASA, to ferry oversized components such as space exploration vehicles. Two of the behemoths, named ‘Pregnant Guppy’ and ‘Mini Guppy’, were powered by their original type of Pratt & Whitney R-4360 Wasp Major piston engines; another, ‘Super Guppy’, was fitted with Pratt & Whitney T-34 turboprop powerplants. Five more — one designated MGT-101, the others SGT-201 — were powered by Allison 501-D22C turboprop engines.

Aero Spacelines Super Guppy — picture credit NASA

The latter type was subsequently used by Airbus Industrie until the late 1990s, to transport large portions of airliners from factories in Europe to Toulouse, France for final assembly. As of November 2019, one Super Guppy was still in use with NASA.

Although never an attractive aircraft, the Model 377 Stratocruiser — which marked Boeing’s post-war return to civil aircraft manufacture — and its ‘descendants’ are testimony to the Seattle company’s 50-plus-year dominance as one of the world’s leading makers of civil and military airplanes.

This is part of a series on the propliners of the 1950s and the slow transition to the jet age. It all began with the DC-3 of course, and my columns move through the other Douglas propliners, the Boeing 377, Lockheed’s Electras and the elegant Constellation. The Brabazon Committee which sparked such a wave of innovation in the UK with the Vickers Viscount, the Bristol Britannia and the ill-fated de Havilland Comet. Many other significant aircraft, such as Avro Canada’s innovative but aborted C-102 passenger jet and the Sud-Aviation Caravelle, which led us into the start of the Jet Age have columns too.

A few quirky segues I couldn’t resist: the ‘Double Sunrise’ flights between my two homelands Ceylon and Australia; the wonderful Carvairs and that very British habit of taking your car on holiday. I also had to write a paean to my beloved A380 and all my pilot friends in the Gulf as COVID ended that little dream.

Thanks for reading and I hope you enjoyed the series as much as I have relished writing them. My special thanks to my old friend, mentor, editor and repository of knowledge Roger Thiedeman, for all the encouragement and support throughout this project.



Suren Ratwatte

I love airplanes and history. Trying to combine both interests in this blog, with stories of the old aircraft and the recollections of those who flew them.