Douglas DC-3

The most famous piston-engined airliner of all time, the DC-3 was
tough, versatile, and economical – a masterpiece of functional design. It was an enlarged version of Douglas’s already successful DC-2, produced in response to a request from American Airlines president, C.R. Smith, for an aircraft to offer comfortable overnight travel.
By increasing the length and girth of the DC-2’s fuselage, Douglas made room for 14 sleeping berths, plus a “honeymoon suite”. The Douglas Sleeper Transport (DST) entered service in July 1936, but it was the conventional passenger version of the same aircraft, in which the extra space was used for more seating instead of bunks, that proved revolutionary.
The DC-3 was cheap to operate, cut journey times, and carried seven more passengers than the DC-2. It transformed airline economics, making passenger transport profitable for the first time. By  1938  the DC-3 was carrying 95 per cent of US airline traffic and serving with 30 foreign airlines. Rugged and reliable, it became one of t be Allies’ principal military transports in World War II, as the C-47 in the United States and as the Dakota in the RAF.  When production ceased in 1947 Douglas bad built 10,654 DC-3s. Thousands served for decades on civilian air routes worldwide.