Douglas DC-2 C-39

The Douglas C-39 was the last DC-2 derivative to leave the Santa Monica factory and, at the same time, the first Army Air Corps transport to incorporate DC-3 components. Carrying the factory designation DC-2-243, it was a composite aircraft: it kept the fuselage and outer wings of the C-33, the cargo version of the DC-2 with a large door on the port side and a reinforced floor, but received the wing centre section, engine nacelles, landing gear and the larger fin and rudder of the DC-3. The bigger tail had first been tried on the sole C-38, which was simply the first C-33 modified with a DC-3 empennage and more powerful engines; Douglas had called it the C-33A before the Air Corps reclassified it as the C-39 prototype. The new tail cured the directional instability that had been one of the few flaws of the DC-2 and C-33, although it is not entirely clear why the Army ordered this hybrid rather than a transport based directly on the DC-3.

The C-39 was powered by two Wright R-1820 Cyclone radials of 975 hp each. Sources disagree on the exact sub-type: the reference encyclopedia gives the R-1820-45, while History of War and Aviations Militaires cite the R-1820-55. Either way, the jump in power over the C-33's 750 hp engines raised the payload from 2,400 to 3,600 lb (about 1,090 to 1,630 kg). As a passenger transport it seated 16; as a freighter it kept the same wide cargo door as the C-33. The figures published by History of War give a wingspan of 85 ft (25.9 m), a length of 61 ft 6 in (18.7 m), a height of 18 ft 8 in (5.7 m), an empty weight of 14,287 lb (6,480 kg) and a loaded weight of 21,000 lb (9,525 kg). Maximum speed was 210 mph (338 km/h) at 5,000 ft, cruising speed 156 mph (251 km/h) at the same altitude, service ceiling 20,600 ft (6,280 m) and normal range 1,170 miles (1,883 km), stretching to a maximum of 1,600 miles (2,575 km).

The Air Corps ordered 37 airframes, serials 38-499 to 38-535, but only 35 were delivered as C-39s between 1938 and 1939. One of the two remaining airframes was completed as the C-42, a VIP transport for the commanding general of GHQ Air Force with 1,000 hp R-1820-53 engines, and the other was delivered as the C-41, which despite being charged against the C-39 order was in fact a DC-3-253 with Pratt & Whitney R-1830 engines, intended for Air Corps chief Oscar Westover and then for his successor, Henry "Hap" Arnold. The last C-39 was delivered in September 1939 and was, literally, the last DC-2 completed: the C-41 and C-42 carried higher type numbers but were built in the middle of the C-39 production run. In 1943 two more C-39s were converted to C-42 standard with their cargo doors bolted shut.

When the United States entered the war, the C-39 was the Air Corps's most numerous multi-engine transport, and it had to fill the gap until the DC-3-derived C-47 and C-53 arrived in quantity. C-39s were called upon for demanding duties in the first months of the conflict, including the evacuation of personnel from the Philippines to Australia in December 1941. Some aircraft operated in the Pacific: 38-505, noted at Nichols Field in the Philippines in August 1941, may have been one of those that escaped from Mindanao in early 1942, and it crashed on take-off from Alice Springs, Australia, on 25 May 1942 through overloading, killing all ten on board. In the United States, the 2nd Transport Squadron loaned C-39s to the newly activated 33rd Transport Squadron in 1942 to haul cargo from Middletown, Pennsylvania, to widely scattered points across the country, Newfoundland, Haiti and Cuba, until the squadron received its first C-53 in June of that year.

The accident record reflects the type's hard use: on 5 March 1942, 38-525 broke up after flying into a storm and fell into the St. Lucie River in Florida, killing seven; on 1 October 1942, 38-524 struck a hill at high speed some 15 miles from Coamo, Puerto Rico, in low visibility, killing all 22 on board in the worst accident in DC-2 history; and on 31 January 1944, 38-501 crashed near Sioux City Army Air Base, possibly after an engine fire, killing its three crew.

The C-39 was the immediate forerunner of the C-47 Skytrain and the link that took the Air Corps from the DC-2 generation to the DC-3 generation. One example survives: 38-515, construction number 2702, held by the National Museum of the United States Air Force at Wright-Patterson, Ohio, and currently in storage.