Canceled Apollo missions planning their own circumlunar flight for December to upstage the Americans once again (see Zond program). McDivitt's crew—who had grown accustomed to working with LM-3 and preparing for its flight—was kept on the D mission which now became Apollo 9, while Borman's crew would fly the CSM lunar orbit mission on Apollo 8, and the E mission was canceled. The swap of crews was also decisive in who would be the first man to walk on the Moon. Pete Conrad was backup Commander for McDivitt's crew, and by the process of crew rotation, would have been in line for Commander
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