class was announced in September 1962. Additionally, he was tasked with making future crew assignments, and assigned Gordon Cooper to Mercury-Atlas 9. In an administrative restructuring in October 1963, Slayton became assistant director of Flight Crew Operations, in addition to his job managing the astronaut office. In November 1963, he resigned from his commission in the Air Force after he was permanently disqualified from flying and became a civilian executive for NASA. After Alan Shepard was grounded due to Ménière's disease, he replaced Slayton as the manager of the astronaut office, while Slayton continued to work for Flight Crew Operations and was promoted to its director in 1966. Slayton continued to be responsible for making crew assignments, and determined the astronauts that would fly on the Gemini and Apollo missions. Slayton created a crew rotation, where a crew would be selected as the backup crew for a mission and would later be the prime crew three missions later. During the Apollo 1 fire, Slayton was in the Cape Canaveral LC-34 blockhouse. He was a close friend of fellow astronaut Gus Grissom and had considered working inside the capsule to determine communications problems and would have worked under the footrests, where the fire would later begin. After the fire, Slayton called a meeting of the astronauts from the first groups to be chosen, in April 1967 and announced that they were the candidates for the first lunar landing. Slayton oversaw the crew reassignments for the upcoming Apollo missions, as well as the selection for Group 6 and Group 7 astronauts. During this time, he continued to show symptoms of atrial fibrillation. After NASA Administrator James Webb decided that Apollo 8 would become a circumlunar mission, Slayton switched the previous crew to the Apollo 9 because of their experience with the lunar module and moved both the prime and backup crew from Apollo 9 to Apollo 8. Due to his crew rotation schedule, the backup crew of Neil Armstrong, Buzz Aldrin and Michael Collins became the primary crew for Apollo 11. Slayton continued to assign the crew for the remaining lunar landings. Slayton chose to replace Ken Mattingly with Jack Swigert on Apollo 13, after concerns arose that Mattingly could develop measles during the mission. In 1969, he made the controversial decision to assign Alan Shepard as the Apollo 13 commander, which was viewed by some astronauts as a conflict of interest,