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 16 the back-up crew for Apollo 13, who had caught it from one of his children. He never contracted the illness, but was nevertheless removed from the crew and replaced by his backup, Jack Swigert, three days before the launch. Young, a captain in the United States Navy, had flown on three spaceflights prior to Apollo 16: Gemini 3, Gemini 10 and Apollo 10, which orbited the Moon. One of 19 astronauts selected by NASA in April 1966, Duke had never flown in space before Apollo 16. He served on the support crew of Apollo 10 and was a Capsule Communicator