Considerable progress is being made by Aerojet-General Corp. to develop a large, high-performance rocket engine (designated M-1) using liquid oxygen and liquid hydrogen propellants and with a nominal thrust rating of 1.5 million pounds. This work is being conducted under contract to NASA and includes component and overall engineering design, engine hardware fabrication, and the construction and/or expansion of testing, manufacturing, and storage facilities. A general description of the M-1 engine and its operation is given, as well as the current status of the various phases of the program. Upon completion of the scheduled preliminary flight rating test (PFRT) program, vehicle integration and experimental flight testing will begin. The M-1 engine system is intended primarily for application in upper-stage propulsion of the next generation large payload class vehicles.