Apollo 9 to land on the Moon; when the crews for Apollo 8 and 9 were swapped, their backup crews were also swapped. Since the rule of thumb was for backup crews to fly as prime crew three missions later, this put Neil Armstrong's crew (Borman's backup) in position for the first landing mission Apollo 11 instead of Pete Conrad's crew, who made the second landing on Apollo 12. Apollo 9 was the first space test of the complete Apollo spacecraft, including the third critical piece of Apollo hardware besides the command and service module and the Saturn V launch vehicle—the lunar
Apollo 9 module. It was also the first space docking of two vehicles with an internal crew transfer between them. For ten days, the astronauts put both Apollo spacecraft through their paces in Earth orbit, including an undocking and redocking of the LM with the CSM, just as the landing mission crew would perform in lunar orbit. Apollo 9 gave proof that the Apollo spacecraft were up to this critical task, on which the lives of lunar landing crews would depend. For this and all subsequent Apollo flights, the crews were allowed to name their own spacecraft (the last spacecraft to have