The Boeing Model 307 Stratoliner was the world's first high-altitude commercial transport and the first four-engine airliner in scheduled domestic service. Its pressurized cabin allowed the airplane to soar above rough weather at an altitude of 20,000 feet -- higher than any other transport of its time. Its circular fuselage provided maximum space for the five crew members and 33 passengers. The nearly 12-foot-wide cabin had space for comfortable berths for overnight travelers.