By the time the United States entered World War II at the end of 1941, the Navy had recognized the need for long-range transport aircraft for both passengers and cargo. This situation led to Pan American Airways teaming with Lockheed Aircraft Corp. and the Navy to develop a new, massive transport plane. PanAm was operating a large fleet of flying boats on long-distance flights, but there would be advantages to using long-range landplanes. The result of this joint effort was the R6O Constellation, the largest aircraft ever flown by the U.S. Navy.
PanAm’s interest in large landplanes led the Douglas and Boeing firms to initiate the Army-sponsored C-74 and C-97 transports, respectively. The Navy sponsored the Lockheed Model 89, with two prototypes being ordered with the designation XR6O-1.1 The plan was for PanAm to operate surplus Navy planes after the war and for the Model 89 to serve as the basic design for a postwar passenger fleet.