Delta IV
In 1994, the United States Air Force Evolved Expendable Launch Vehicle (EELV) program led to the development of the Delta IV. Rocketdyne realized that they would need a powerful, simple engine for the proposed liquid-fueled Common Booster Core (CBC). NLS research on the STME, a simpler SSME, served as a starting point for the greatly simplified RS-68 that powered the Delta IV EELV rocket. The Delta IV Heavy rocket is composed of three CBCs.