During World War II Stratoliners were employed as military transports (C-75s), flying principally to South America and across the Atlantic. In 1951 the ex-TWA machines, replaced the Four 900 hp (671-kw) Wright GR-1820 Cyclone radial piston engines, with Wright Cyclone 1,200 hp (894 kw) engines. The wings were replaced with B-17G wings. They were then sold to Aigle Azur in France, operating to French IndoChina. Here they became involved with the Vietnam War, worked with operators such as Air Laos and were still flying into the 1960s.
CIVILIAN VERSION:
Boeing Model 307 Stratoliner was the first fully pressurized airliner to enter service anywhere in the world, Boeing's 33-seat Model 307 Stratoliner of 1938 employed the wings and tail surfaces of the B-17C Flying Fortress.
Boeing's Model 299, prototype for the military bomber aircraft which duly became the B-17 Flying Fortress, was developed in parallel with a civil version of the same aircraft which had the company designation Boeing Model 300. The Model 307, or Stratoliner, was a straightforward conversion from the supremely successful B-17 Flying Fortress bomber. The Boeing 307 was developed to start another era, that of pressurized comfort at higher altitudes than had been previously contemplated.
The aircraft was the result of considerable research in high altitude flying by "Tommy" Tomlinson, of TWA, who was estimated to have flown more hours above 30,000 feet than all other pilots combined. With his recommendations, Boeing produced an airliner which could cruise at 14,000 feet, or described as at the time, "above the weather."
The Boeing 307 first flew on December 31, 1938 and TWA put it into service on the transcontinental route on 8 July 1940, reducing the time to 13 hrs 40 min, and cutting two hours off the DC-3's.
