During 1947 Fairchiid developed an improved version of the C-82, the XC-82B prototype being a conversion from a production C-82A. It differed primarily by having the flight deck resited into the nose of the aircraft and the installation of 1976kW Pratt & Whitney R-4360-4 Wasp Major 28-cylinder radial engines. Following service tests it was ordered into production as the C-119B Flying Boxcar (55 built), these having the fuselage widened by 0.36m, structural strengthening for operation at higher gross weights, and more powerful R-4360-20 engines. Accommodating up to 62 paratroops, and with increased cargo capacity, the C-119s gave excellent service during operations in Korea and Vietnam, as well as in a wide variety of other heavy transport applications. C-119s also serve or served with the air forces of Belgium, Brazil, Ethiopia, India, Italy, Nationalist China and South Vietnam, many supplied under the Military Assistance Program. In addition, some surplus military aircraft, both C-82s and C-119s, were acquired by civil operators.

In 1961 Steward-Davis Inc. of Long Beach, California, developed a Jet-Pak conversion for C-119 aircraft. This involved the installation of a 1542kg thrust Westinghouse J34-WE-36 turbojet engine in a specially-developed nacelle mounted on the upper surface of the wing centre-section. At least 26 Indian Air Force C-119s had a more powerful HAL-built Orpheus jet pod to enable them to operate with greater payloads under 'hot and high' conditions.