In mid-1966, Schirra was assigned to command a three-man Apollo crew with Donn F. Eisele and R. Walter Cunningham to make the second crewed flight test of the Apollo Command/Service Module, with a mission profile identical to Apollo 1. Schirra argued against a repeat mission, and his crew became the backup crew for Gus Grissom, Ed White, and Roger Chaffee. Schirra's crew conducted tests in the command module on January 26, 1967, and were en route to Houston the next day when Grissom and his crew were killed in a fire during a test. Schirra's crew became the prime crew of the first crewed flight. This became Apollo 7 in the program's revised mission numbering plan, and was delayed until the fall of 1968 while safety improvements were made to the Command Module.