The F-1 is a rocket engine

Rocket engine

A rocket engine, or simply "rocket", is a jet engineRocket Propulsion Elements; 7th edition- chapter 1 that uses only propellant mass for forming its high speed propulsive jet. Rocket engines are reaction engines and obtain thrust in accordance with Newton's third law...

 developed by Rocketdyne

Rocketdyne

Rocketdyne was a Rocket engine design and production company headquartered in Canoga Park, California, United States. The company was related to North American Aviation for most of its history. NAA merged with Rockwell International, which was then bought by Boeing in December, 1996...

 and used in the Saturn V

Saturn V

The Saturn V was an American human-rated expendable rocket used by NASA's Apollo and Skylab programs from 1967 until 1973. A multistage liquid-fueled launch vehicle, NASA launched 13 Saturn Vs from the Kennedy Space Center, Florida with no loss of crew or payload...

. Five F-1 engines were used in the S-IC

S-IC

The S-IC was the first stage of the Saturn V rocket. The S-IC first stage was built by The Boeing Company. Like the first stages of most rockets, most of its mass of over two thousand metric tonnes at launch was propellant, in this case RP-1 rocket fuel and liquid oxygen oxidizer...

 first stage of each Saturn V, which served as the main launch vehicle in the Apollo program. The F-1 is still the most powerful single-chamber liquid-fueled rocket engine ever developed. The RD-170

RD-170 (rocket engine)

The RD-170 is the world's most powerful liquid-fuel rocket engine, designed and produced in the USSR by NPO Energomash for use with Energia launch vehicle...

 has slightly more thrust, using a cluster of four smaller combustion chambers and nozzles.
The F-1 was originally developed by Rocketdyne to meet a 1955 US Air Force

United States Air Force

The United States Air Force is the aerial warfare service branch of the United States Armed Forces and one of the American uniformed services. Initially part of the United States Army, the USAF was formed as a separate branch of the military on September 18, 1947 under the National Security Act of...

 requirement for a very large rocket engine.