Apollo 10

Apollo 10 acted as the dry run for the Apollo 11 to land on the moon. The crew consisted of Thomas Stafford as the commander. John Young was the command module pilot, and Eugene Cernan was the lunar module pilot. Once in orbit around the moon, Cernan and Stafford took the lunar module to the moon and practiced the normal landing procedure that would be used by future Apollo missions. This LEM was never meant to actually land on the moon. If the astronauts had decided to land on the surface, the LEM didn't contain enough fuel in the ascent module, so they would have been stranded on the lunar surface. The LEM did come within 8.4 nautical miles of the lunar surface. After this run, the LEM docked with the command module again and headed back to Earth. Each crew member would return to space. Young and Cernan would both return to the moon while Stafford would command an Apollo-Soyuz mission.

With the path cleared, Apollo 11 could land on the moon.