This is a segment of the injector of the Reaction Motors, Inc. (RMI) 6000-C4 rocket engine, also designated the XLR-11. The engine is of the same kind used in the Bell X-1 rocket research aircraft, which was the first plane to achieve the speed of sound on 14 October 1947. The engine used liquid oxygen and alcohol and produced 6,000 pounds of thrust. Developed from 1945, it was used in a variety of rocket research aircraft besides the X-1. These included the X-1A, X-1B, X-1D, and X-1E, as well as the Douglas D-558-2 Skyrocket and the Republic XF-91 fighter.

Two of the chambers served as the "Interim Engine" for the X-15 research aircraft during 1959-1961, while that aircraft's 50,000-pound thrust XLR-99 engine was completing its development. The engine also powered NASA aerodynamic test craft called Lifting Bodies (the HL-10, MS-F3, X-24A, and X-24B). In 1948, uprated chambers of the same engine, each producing 2,000 pounds of thrust, powered the MX-774 test missile, a predecessor of the Atlas missile. The 6000C-4 thus saw an active service life from 1947-1975, when it was last used in the X-24B.

Robert Holder donated this to the Museum in 2001.