The RS-68 engine is the first large liquid-fueled engine to be developed in the United States since the SSME (Space Shuttle Main Engine).  The RS-68 is designed to power the first stage of Boeing's Delta IV (EELV) launch vehicle.

The RS-68 is a gas generator liquid oxygen / hydrogen booster engine.  From the outset, the RS-68 was designed to be simple and inexpensive to build.  The bell-nozzle RS-68 develops 650,000 lb of sea level thrust and utilizes a simple design philosophy which has drastically reduced the total part count when compared to engines of equivalent size or performance.