North Central Airlines model plane. Undoubtedly a classic airliner, and almost certainly as well known to travelers all over the world as to aviation enthusiasts, by the end of 1991 the Douglas DC-3 as a type, had been in service continuously for 55 years, with a safety record that has become almost legendary. Civil DC-3s delivered to US airlines before the nation became involved in World War II played a most important part in the development of reliable national air routes. It has been recorded that in the period 1936-1941 national passenger mileage in the US increased by almost 600 per cent, a growth that was very largely due to the DC-3, which was the primary airplane of most US airlines in this period. The DC-3's rugged reliability also appealed to military planners as soon as the requirement for large numbers of transport airplanes was appreciated.