The XLR11 was the first liquid-fuel rocket engine developed in the United States for use on airplanes. Designed and built by Reaction Motors, the engine used ethyl alcohol and liquid oxygen (LOX) as propellants to generate a maximum thrust of 6,000 lbs. Thrust could be varied by operating the XLR11's four combustion chambers individually or in combination. The engine was first used in the Bell X-1 in 1947.

Credits - U.S. Air Force Museum