DC-3

American Airlines challenged Douglas to build a sleeper aircraft that could fly coast-to-coast with only three stops. The result was the DC-3, which entered service in 1936 and immediately transformed the airline industry. For the first time, airlines could make money carrying passengers alone, without mail subsidies. The DC-3 carried 21 passengers in comfort at 185 mph, and it was rugged enough to operate from grass strips. When WWII began, the military version (C-47 Skytrain) became the backbone of Allied air transport, dropping paratroopers on D-Day and supplying forces across every theater. Eisenhower named it one of the four tools that won the war. Remarkably, several DC-3s remain in commercial service today, nearly 90 years after the type first flew.