Boeing 367 Stratofreighter (C-97) and 377 Stratocruiser
Updated: Jul 16
Like many other aircraft produced at the end of World War II, the Model 367 was derived from a heavy bomber of the time. In the 367’s case, a new fuselage was married to the wings, tail, undercarriage and engines of the B-29 Superfortress to produce a long-range strategic transport able to carry a 35,000-lb. payload or up to 130 fully-equipped troops. As the C-97, it went on to become the United States Air Force’s principal airlifter and air-refueling tanker, remaining in service until 1978. A commercial development, the Model 377, was acquired by Pan American Airways, Scandinavian Airline System, American Overseas Airlines, Northwest Airlines, British Overseas Airways Corporation and United Air Lines. Boeing considered further developments but only the turbojet-powered 367-80 progressed beyond the drawing board, leading to the 707 and C-135.
A number of Strats have been modified to carry outsize cargo under the generic name Guppy. The last of these, assembled in France for Airbus Industrie from parts of various surplus C-97s, is currently the only Strat still active, having been provided to NASA by the European Space Agency (ESA) under a barter agreement to offset the cost using NASA’s Space Shuttle to carry ESA payloads to the International Space Station. Having completed the 15-year restoration of their C-97G in 2017 only for the aircraft to sustain a catastrophic failure of No.2 engine less than two years later, the Berlin Airlift Historical Foundation has obtained a substantial cache of parts, and it is hoped that N117GA will rejoin the air display circuit later this year. No Model 377 survives.
First flight: 367 - 9 Nov 44 (c/n 8481, 43-27470); 377 - 8 Jul 47 (c/n 15922, NX90700)
Production: 943, at Renton, WA, comprising 888 367s and 55 377s.
First delivery: 367 - 1947, to United States Air Force (c/n 15712, 45-59587); 377 - 19 Mar 49, to Pan American (c/n 15923, N1023V).
Last delivery: 367 - not known; 377 - 24 Mar 50, to BOAC (c/n 15979, G-AKGM).
Variants: Model 367-1-1 (XC-97) - prototype powered by 4 Wright R-3350-57A radials, featuring twin cabins, one above the other, with accommodation for 134 fully-equipped troops (3 built);
Model 367-5-5 (YC-97) - test version (6 built);
Model 367-4-6 (YC-97A) - test version powered by 4 Pratt & Whitney R-4360 Double Wasps and featuring a taller tail, nosewheel steering and other improvements (3 built);
Model 367-4-7 (YC-97B) - personnel transport version of YC-97A;
Model 367-4-19 (C-97A) - initial production version based on YC-97A but featuring AN/APS-42 search radar in a chin-mounted radome, increased fuel capacity and, in later aircraft, a forward cargo door (50 built);
Model 367-4-29 (C-97C) - C-97A with detail changes (14 built) and KC-97E - C-97C optimized for air refueling powered by improved Pratt & Whitney R-4360-35C engines and featuring additional fuel tanks and and refueling boom (60 built);
Model 367-76-29 (KC-97F/G) - improved version of the KC-97E powered by Pratt & Whitney R-4360-59B engines and, featuring, on the KC-97G, the ability to operate as a cargo transport without removal of the refueling equipment (159 built as KC-97F and 592 as KC-97G);
Model 377 Stratocruiser - long range airliner with seating for up to 100 passengers, based on the YC-97A.
Conversions: US Air Force conversions included an unknown number of Air National Guard KC-97Gs to KC-97L through the addition of a pair of J47 jet engines in order to ensure they could keep up with the jets they were refueling, as well as:
135 KC-97Gs to C-97Gs for use by the Air National Guard as cargo transports;
3 C-97Gs to EC-97G for testing of electronic equipment;
29 KC-97Gs to HC-97G for search and rescue;
2 KC-97G to YC-97J for use in trials of the YT34-P-5 turboprop engine;
27 KC-97Gs to C-97K passenger transports;
Rebuilds for the carriage of outsize cargo: 377PG Pregnant Guppy, by On Mark Engineering at Van Nuys, CA, with 29,000-lb. payload (1 built, using an ex-Pan American 377 as the ‘airframe of reference’; first flight 19 Sep 62);
377SG Super Guppy by On Mark Engineering at Van Nuys, CA, with 40,000-lb. payload and swing-nose (1 built, using the 2 YC-97Js and an ex-Pan American 377, and retaining the former’s Pratt & Whitney YT34 turboprops; first flight 31 Aug 65);
377MG Mini Guppy by Aero Spacelines at Santa Barbara, CA, with 41,100-lb. payload and swing-tail (1 built, from an ex-Pan American 377; first flight 24 May 67);
377MGT Mini-Guppy Turbine by Aero Spacelines at Santa Barbara, CA, with 62,925-lb. payload and powered by Allison 501-D22C turboprops (1 built; first flight 13 Mar 70)
377SGT Super Guppy 201, with 54,500-lb. payload and Allison 501-D22C turboprops (2 built by Aero Spacelines at Santa Barbara, CA, and 2 by UTA Industries at Paris-Le Bourget; first flight 24 Aug 70. For the most part, these aircraft use various surplus C-97s, although the lower aft fuselage of the Pregnant Guppy does live on in the fourth 377SGT).