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In 1935 with design work for the B-17 well underway, Boeing decided to create a civilian airliner from the same basic design. Borrowing the wings, engines, landing gear and tail from the B-17 and marrying them to a new cylindrical fuselage designed to be pressurised, the new Model 307 promised much better performance than existing airliners. It could cruise at an altitude of 20,000ft, unlike contemporary planes that had to remain below 15,000ft. With the plane having the ability to fly higher than most weather systems, Boeing gave it the name “Stratoliner”.
Despite the advances promised by the 307, orders were relatively few. The first plane was destroyed when it crashed during a demonstration flight for Dutch airline KLM. Pan Am ordered two Stratoliners and later an additional four, and Trans World Airlines five. The first delivery was to the eccentric tycoon and adventurer Howard Hughes, who bought it for a round-the-world record attempt that was abandoned when Germany invaded Poland in September 1939. Pan Am took delivery of just four 307s before the war put an end to civilian aircraft production but TWA received all five that they ordered. These were named after native American tribes – Apache, Comanche, Navajo, Cherokee and Zuni.
With the outbreak of war in 1941 Pan Am’s 307s remained nominally in civilian service but were under the direction of the Army Air Forces’ Air Transport Command. These were assigned to fly on South American routes for the AAF. The five TWA planes were bought by the AAF and received the military designation C-75 but were flown by their original TWA crews under contract. These were assigned to ATC and initially flew two transatlantic routes: the northern route from Gander to Prestwick, and the southern one from Natal to Accra in the south.
For the first year of the war the C-75s were the only planes capable of nonstop transatlantic flight, although they had the pressurization gear removed and additional fuel tanks installed to make these flights more comfortable. These aircraft regularly flew ‘top brass’ across the Atlantic, including members of the Chiefs of Staff and Harry Hopkins, Roosevelt’s personal aide. A C-75 was also dispatched to China to collect the Doolittle raiders after all of their B-25s were lost.
In 1944 with sufficient numbers of purpose-built military transports available, the C-75s were reconditioned and sold back to TWA. They continued to serve the civilian market for years after the war, although seven were lost to accidents. One 307 serving with the French airline Aigle Azur may have been accidentally shot down by anti-aircraft fire during the Vietnam War in 1965.
Boeing C-75 Stratoliner Specifications
Boeing C-75 StratolinerRoleTransportCrew5: Pilot, co-pilot, engineer, 2 cabin crewPowerplant4x Pratt & Whitney R-1820-G102A (1,100hp)Speed215mph (cruise)
241mph (max)Ceiling23,300ftRange1,750 miles (internal)ArmamentOrdnanceDimensions74ft 4in (length)
107ft 0in (wingspan)
20ft 10in (height)Wing Area1486 sq.ft.Weight30,000lb (empty)
45,000lb (gross)
Number produced5
