Northwest Flight 2501 utilized a Douglas DC-4 airliner with four Pratt & Whitney, R-2000 “Wasp” engines that could generate 1,450 horsepower each. These reciprocating piston, propeller engines could power the converted World War II C54 transport to a cruising airspeed of 180 miles per hour. The development of the DC-4 dated back to 1938 when United Airlines conceived the first four-engine, long-range airliner. They hired Douglas to devise the highly ambitious DC-4E (“E” for experimental). This four-engine behemoth was flight tested in 1939. It was roughly three times the size of its predecessor, the DC-3, with a wingspan of 138 feet and a length of 97 feet. It could potentially fly nonstop from Chicago to San Francisco. However, the DC-4E never flew commercially.
Boeing could not get beyond the prototype. All the groundbreaking new technology on the DC-4E meant that it was costly, complex and had higher than anticipated operating costs, so Douglas thoroughly revised the design, resulting in the smaller and simpler definitive DC-4.
The first C-54s were first delivered on March 20, 1942, and the U. S. Army Air Force commandeered them right off the assembly line .They saw service in every theater of World War II. In time, they became the military’s primary transport aircraft to operate across both the Atlantic and Pacific Oceans. The plane was given the military designation C-54. Production orders followed and, to meet the demand, Douglas started a second assembly line in Chicago, Illinois, which would eventually produce nearly 60 percent of all C-54s built. The plane later used by Northwest for Flight 2501 was special in its own right: It was the first C-54 off the production line in August of 1943, dubbed Chicago Skymaster. Fifty-thousand people gathered for a celebretory dedication and watched its first flight.
In the three years prior to V-J Day, C-54 crews made nearly 80,000 crossings of the North Atlantic and only three aircraft were lost. The first dedicated Presidential aircraft was the lone VC-54C, which was modified with a special hydraulic lift for Franklin Delano Roosevelt’s wheelchair. Nicknamed “Sacred Cow,” the aircraft was used to take FDR to the Yalta Conference. President Harry S. Truman signed the National Security Act of 1947, creating an independent Air Force, while on board this aircraft on July 12, 1947. The “Sacred Cow” is now on display at the US Air Force Museum in Dayton, Ohio.
Winston Churchill, General Douglas MacArthur, and General Dwight David Eisenhower used C-54s as their personal aircraft. On September 2, 1945, a C-54 crew made a record run of 31 hours, 25 minutes between Tokyo, Japan, and Washington, D. C., to deliver the first films of the Japanese surrender ceremony on board the U. S. Navy battleship USS Missouri.
Later, at the height of the Berlin Airlift, 319 of the roughly 400 C-54s in service were hauling supplies to the besieged city. On September 30, 1949, a C-54 crew made the last flight of the Berlin Airlift when it lifted off from Rheine-Main Air Base in West Germany.
As was the case with the earlier DC-3 or C-47, the end of war meant that many of the aircraft were declared surplus and sold to the world’s fledgling commercial airlines, which converted the interiors for passenger service. Subsequently, Douglas built 78 additional DC-4s to fill new orders. The plane used for Flight 2501 was originally operated by the United States Air Force and later sold to Linea Aeropostal Venezolana, then purchased by Northwest Airlines on April 11, 1947, and renumbered N-95425. It began cargo service on June 25, 1947. On April 25, 1950, one month before the tragic accident, it was converted to a 55-passenger cargo-coach aircraft.