On 18 August 1950, the United States Navy signed a contract for 11 military transport versions of the Lockheed L-1049.

The aircraft entered evaluation service in the Navy's oldest test squadron, VX-1, based in Patuxent River, Maryland.

On one occasion, Lockheed test pilot Roy Wimmer managed to reach a top speed of 479 mph (416 kn; 771 km/h) in the YC-121F during a 20 degree dive.

On 25 January 1957, a new transcontinental record for propeller aircraft was set by a YC-121F which flew from Long Beach to Andrews AFB, Maryland, in four hours and 43 minutes.

This would have had the fuselage of the L-1049E and be equipped with extra fuel tanks on the wingtips as well as four 5,500 hp (4,100 kW) Pratt & Whitney PT-2F1 turboprops (the planned civilian version of the YT34).

When the L-1249A finished service with both the Navy and Air Force, the four existing airframes were used to build civilian L-1049 Super Constellations.

For example, the two YC-121F fuselages were attached to the wings engines and tails of two used L-1049G aircraft to make two L-1049H freighters for the Flying Tiger Line.

[4][5][6] Data from Lockheed Constellation: from Excalibur to Starliner Civilian and Military Variants[5], YC-121F Charactaristics Summary[7]General characteristics Performance