Boeing 307 Stratoliner

The Boeing Model 307 Stratoliner was an American four-engine airliner derived from the B-17 Flying Fortress bomber, and it was the first airliner in revenue service with a pressurized cabin. Pressurization and supercharged engines let it cruise above the weather at about 220 miles per hour at 20,000 feet, well above the Douglas DC-3. It was also called the Strato-Clipper in Pan American service and the C-75 in United States Army Air Forces service. The first aircraft flew on 31 December 1938, commercial service began in July 1940, and only ten were built, with seating that later grew from 33 passengers to as many as 60.