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The Boeing C-75 was the military designation given to five Model 307 Stratoliners that were commandeered by the USAAF in 1942.
The Stratoliner used the wings, nacelles, engines and tail from the B-17C Flying Fortress, although with leading edge slots on the wing tips. An entirely new fuselage was produced, with a circular cross-section. The new fuselage was wider and with a larger internal area than the B-17 fuselage, and the wingspan thus increased from 103ft 9in to 107ft 3in. The Stratoliner was the first commercial airline to have a pressurized cabin as it was designed to fly as much higher altitudes than previous transport aircraft. Only ten Stratoliners were built. The prototype was lost in a crash while being tested. Five were built for TWA (then Transcontinental and Western Air), four for Pan American Airways and one for Howard Hughes.
On 31 December 1941 President Roosevelt signed an executive order allowing the Secretary of War to commandeer any part of the civilian airline industry needed for the war effort. This produced fifteen four-engined transports, mainly flying boats. The only land aircraft were the five Boeing 307 Stratoliners that were taken from TWA along with their commercial crews. Pan American's four aircraft were also used in the war effort, although retained their civil designation.
The C-75s were given extra fuel tanks and were used as transatlantic transport aircraft. In February 1842 Transcontinental and Western Air, with two C-75s, begin flying between Washington and Cairo. The main use of the type was across the South Atlantic.
The biggest problem with the C-75 was that it could only carry 4,100lb of cargo at maximum range, and so it was never considered for wartime production.
Engine: Four Wright GR-1820 Cyclone radials
Power: 900hp each
Crew: 5
Span: 107ft 3in
Length: 74ft 4in
Height: 20ft 9in
Empty Weight: 30,310lb
Loaded Weight: 42,000lb
Maximum Speed: 246mph
Cruising Speed: 220mph
Climb rate: 1,200ft/ min
Ceiling: 26,200ft
Range: 2,400 miles
Payload: 4,100lb at maximum range