The Saturn V Rocket, which carried astronauts to the Moon, used its own inertial guidance system, separate from the guidance systems on the Command and Lunar Modules. This system was contained in an "Instrument Unit" (IU): 1 meter (3 feet) high by 6.7 meters (22 feet) in diameter, located between the third stage of the Saturn rocket and the payload. In the case of Apollo 12, this guidance system kept the rocket on course after a lightning strike during launch.