Spacecraft
Preliminary design studies of Apollo spacecraft began in 1960 as a three-man command module supported by one of several service modules providing propulsion and electrical power, sized for use in various possible missions, such as: shuttle service to a space station, circumlunar flight, or return to Earth from a lunar landing. Once the Moon landing goal became official, detailed design began of the Command/Service Module (CSM), in which the crew would spend the entire direct-ascent mission and lift off from the lunar surface for the return trip. The final choice of lunar orbit rendezvous changed the CSM's role to a translunar ferry used to transport the crew and a new spacecraft, the Lunar Excursion Module (LEM, later shortened to Lunar Module, LM), which would take two men to the lunar surface and return them to the CSM.
Read more about this topic: Apollo Program