The Douglas DC-3 revolutionized air transportation and airline service during the 1930s and 1940s. It was a luxury airliner that boasted cabin heat and running water in its on-board lavatory. With the right balance of efficiency, range, speed, and payload, the DC-3 was the first aircraft to earn a profit for its owners just by carrying passengers. The hero of early airlines, a handful of DC-3s are still at work today.