Five J-2 engines powered the Saturn V’s second stage, known as the S-II stage. They were arranged in a quincunx pattern, with four engines surrounding one central engine.
The S-II followed the Saturn V’s first stage, separating after the rocket had cleared the densest part of Earth’s atmosphere. Its five engines burned liquid hydrogen and liquid oxygen, producing the thrust needed to accelerate the Apollo spacecraft toward orbit. The center engine was shut down early during flight on many missions to reduce longitudinal pogo oscillations, while the four outer engines continued operating.
The number is easy to confuse with the Saturn V’s complete engine count. The first stage used five F-1 engines, the second stage used five J-2 engines, and the S-IVB third stage used one J-2 engine. Thus, the second stage alone had five J-2s, while the upper stages together used six J-2 engines across the S-II and S-IVB.
The S-II was built by North American Aviation. It flew from Apollo 4 through the final Saturn V launch for Skylab in 1973.