Apollo 9 in early 1969. However, LM problems again prevented it from being ready for the D mission by December, so NASA officials created another mission for Apollo 8 using the Saturn V to launch only the CSM on the first crewed flight to orbit the Moon, and the E mission was cancelled as unnecessary. Slayton asked McDivitt and Borman which mission they preferred to fly; McDivitt wanted to fly the LM, while Borman volunteered for the pioneering lunar flight. Therefore, Slayton swapped the crews, and McDivitt's crew flew Apollo 9. The crew swap also affected who would be the first crew
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