After Armstrong served as backup commander for Apollo 8, Slayton offered him the post of commander of Apollo 11 on December 23, 1968, as Apollo 8 orbited the Moon.
Setelah Armstrong menjadi komandan cadangan Apollo 8, Slayton menawarkan jabatan komandan Apollo 11 pada 23 Desember 1968, saat Apollo 8 mengorbit Bulan.