Douglas DC-4 C-54E

The C-54E was the fifth production version of the Douglas C-54 Skymaster, the military derivative of the DC-4, and the second-to-last to reach the assembly line. Its purpose was to finish a process that had begun with the original C-54: clearing the cabin of the auxiliary fuel tanks that the USAAF had demanded in order to give the aircraft the transoceanic range it required. The first C-54s taken from the civil line carried four tanks in the main cabin, cutting seating to 26; the C-54B moved part of that capacity into the wing, and the C-54D, which entered service in August 1944, added the more powerful R-2000-11 engines. On the C-54E the last two tanks still occupying the cabin were removed and replaced by collapsible bag-type tanks fitted into the inner wing sections. Total fuel capacity settled at 3,520 US gallons, slightly less than its predecessor, but in return the cabin was clear from end to end.

That recovered space was the version's second defining feature. The C-54E interior was designed to allow a rapid switch between three layouts: pure freighter, 50-seat troop transport or 44-seat staff transport. Period documentation summarises it as a "further revision to fuel tanks and provision for rapid conversion from passenger to cargo", and that flexibility was exactly what Air Transport Command wanted for a worldwide route network on which the same airframe might fly out loaded with materiel and return carrying personnel. The engines remained the fourteen-cylinder Pratt & Whitney R-2000-11 Twin Wasps of the C-54D, rated at 1,350 hp for take-off.

Douglas built 125 C-54Es. Maintenance manuals for the series list both the C-54E and the C54E-DC designation, showing that airframes came from the Chicago (Orchard Place) plant as well as Santa Monica; the Illinois factory in fact built more Skymasters overall (655 against 515). Twenty C-54Es went to the United States Navy as the R5D-4; some were later given a passenger-only fit as the R5D-4R, and two R5D-4s were equipped with special electronics for the Coast Guard. Under the 1962 unified designation system the surviving R5D-4s became EC-54Us and the R5D-4Rs became C-54Rs.

The C-54E's postwar career was long and varied, and it spawned several conversion sub-variants. AC-54Es received airways calibration equipment and were redesignated EC-54E in 1962; SC-54Es were adapted for air-sea rescue and became HC-54Es in 1962; and VC-54Es served as staff transports, joined in the 1960s by a further eight E airframes rebuilt as VIP transports. During the Berlin Airlift, between June 1948 and September 1949, 38 C-54Es had their interiors stripped completely so they could lift an extra 2,500 lb of coal, receiving the designation C-54M; one German source puts the number of conversions at 27. In the Korean War, 30 C-54Es were rebuilt as MC-54M aeromedical evacuation aircraft, able to carry 30 stretchers and the attending medical staff.

The C-54E was also the basis for Douglas's experiments with inline engines: the XC-114 was a stretched C-54E powered by four Allison V-1710s, of which a single example was built; the XC-115, with Packard V-1650s (the licence-built Merlin), never left the drawing board; and the YC-116, derived from the XC-114 with thermal de-icing in place of rubber boots, served as a test-bed for that system. The production version that followed the E, the C-54G, was identical except for its R-2000-9 engines with higher take-off power.

At least one airframe survives: C-54E 0-50582 is on static display at the KAI Aerospace Museum in Sacheon, South Korea. The sources consulted give no breakdown of production batches or of the specific civil operators that flew surplus C-54Es after the war.