Boeing's C-97 was the Army Air Forces cargo and transport version of the B-29. Between 1943 and 1950, 74 Stratofreighters were ordered, and the first flight occurred on 15 November 1944. A tanker version, the KC-97, was introduced in 1950 using the flying boom refueling system, and all subsequent USAF contracts for C-97s were for tankers. In all, 890 aircraft were ordered: 74 C-97s and 816 KC-97s. After 1956, USAF KC-97s were gradually replaced by KC-135 jet tankers, but some were modified for continued use in other roles. In 1964, selected aircraft were returned to a tanker configuration as KC-97Ls, primarily for the Air National Guard. Two jet engines were added to increase speed and altitude, making the tankers more compatible with high-performance jet aircraft. Although the last USAF C/KC-97 was retired in 1973, examples remained in use with the AF Reserve and ANG as tankers or air-sea search and rescue aircraft for several years before the last one was retired. During the 1950s and 1960s, KC-97 tankers were stationed at Robins AFB with the 19th Bombardment Wing in support of the B-52 bombers assigned to the wing. This KC-97L was delivered to the USAF in January 1956 and served with various units around the world before being retired in 1977. It was then sold to a commercial user, later acquired through an exchange, and flown to the Museum in 1986. Its specifications were a wingspan of 141 feet 2 inches, length of 117 feet 5 inches, height of 38 feet 4 inches, maximum weight of 153,000 pounds, no armament, four Pratt and Whitney R-4360 engines of 3,500 horsepower each and two General Electric J47 jet engines of 5,970 pounds of thrust each, a cost of $1,205,000, serial number 53-298, maximum speed of 400 miles per hour, cruising speed of 230 miles per hour, range of 2,300 miles, and service ceiling of 30,000 feet.