The XLR-11 rocket engine, originally designated 6000C-4 by its manufacturer, Reaction Motors, Inc. (RMI), is of the same kind used in the Bell X-1, the first plane to achieve the speed of sound on October 14, 1947. Each of the chambers could be fired separately, delivering 1,500 pounds of thrust per chamber. This particular XLR-11 is one of two which powered the first test flights of the X-15.
The engine was developed from 1945 and, with minor modifications, was used on a variety of rocket research aircraft besides the X-1. Two of the 4-barrel motors, or engine, served as the "Interim Engine" for the X-15 while its XLR-99 engine was under development. The engine also powered several NASA aerodynamic test craft called Lifting Bodies. The 6000C-4 saw an active service life from 1945-1975, when it was last used in the X-24B.
Transferred to NASM from the U.S. Air Force in 1963.