This is the XLR-11, also called the 6000C-4, one of the most widely used U.S. liquid-propellant rocket engines that powered the Bell X-1 and other rocket research aircraft. Developed by Reaction Motors, Inc. in 1945, it produced a maximum thrust of 6,000 pounds from its four combustion chambers. The engine's most famous application was powering the X-1, the first plane to reach the speed of sound on 14 October 1947.
It was also used in the X-1A, X-1B, X-1D, X-1E, Douglas D-558-1 Skyrocket, and XF-91. Two tandem 6000C-4's served as the Interim Engine for the X-15 from 1960-1961, and it also powered several NASA Lifting Bodies (the HL-10, MS-F3, X-24A, and X-24B). This object was donated to the Smithsonian in 1952 by Reaction Motors, Inc.
Reaction Motors, Inc.