When it got out of the Boeing workshops in 1937, the 307 model, also known as the Stratoliner, had many similarities with the famous B-17 Flying Fortress, of the same company. Unlike the latter, though, a huge and unpleasant bomber, the 307 was concieved as a small comfortable commercial airplane with a 33-passanger capacity. This comfort comes, not only from the fact that its interior is pressurised, allowing it to travel at great altitudes, above turbulence, but also, the cylindric shape of its fuselage is responsible for its spacious interior. You could say the 307 set the pattern for modern airplanes: a four-engined, pressurised plane with a five-member crew, including a flight engineer.
Ten copies of this model had been built when WWII broke out and production stopped while every effort went into building military models, such as the B-17. The excentric millionaire Howard Hughes bought one that belonged to the TWA fleet and turned into the first aerial executive means of transportation. Industrial designer Raymond Loewy was in charge of its masterly interior, following suggestions by actress Rita Hayworth, so it's said... Nowadays, there is only one copy of this superb plane, that has been completely restored by the National Air & Space Museum.