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 4 the first mission to fly under the official Apollo mission numbering scheme approved by Mueller on April 24, 1967. Since the failed first manned flight had been designated Apollo 1 in honor of the crew widows' wishes, and three unmanned Apollo/Saturn IB flights had already occurred, Mueller resumed the numbering sequence at Apollo 4. The vehicle's on-pad, pre-launch tests and preparation practice started in September, and encountered several problems with propellant loading and various equipment failures. These pushed the launch into November, but provided valuable lessons learned on the new vehicle. By this time, North American had been purchased by