The Aerojet-General M-1 was the largest and most powerful liquid hydrogen-fueled rocket engine to be designed and built. It offered a baseline thrust of 1.5 million pounds force and 1.8 million pounds force as its immediate growth target. The M-1 was larger and produced more thrust than the famed Rocketdyne F-1 that powered the first stage of the Saturn V rocket to the moon.
Many designs of the post-Saturn Nova launch vehicles made use of the M-1 rocket engine.
http://en.wikipedia.org/wiki/M-1_%28rocket_engine%29
Edit: Removed reference to M-1 being used on Titan for Dynasoar
The M-1 Rocket Engine Project by Walter F. Dankhoff, Lewis Research Center, Cleveland Ohio
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19730065121_1973065121.pdf
Development of a 1,500,000-lb-thrust /nominal vacuum/ liquid hydrogen/liquid oxygen engine Final report, 30 Apr. 1962 - 4 Aug. 1966 by Aerojet-General Corporation
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19680006392_1968006392.pdf
Many designs of the post-Saturn Nova launch vehicles made use of the M-1 rocket engine.
http://en.wikipedia.org/wiki/M-1_%28rocket_engine%29
Edit: Removed reference to M-1 being used on Titan for Dynasoar
The M-1 Rocket Engine Project by Walter F. Dankhoff, Lewis Research Center, Cleveland Ohio
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19730065121_1973065121.pdf
Development of a 1,500,000-lb-thrust /nominal vacuum/ liquid hydrogen/liquid oxygen engine Final report, 30 Apr. 1962 - 4 Aug. 1966 by Aerojet-General Corporation
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19680006392_1968006392.pdf