This unit became the 471st Naval Special Weapons Unit on its certification in August 1948.[26] Two Air Force units were created in September and December 1948, which became the 502d and 508th Aviation Squadrons. An additional Army special weapons unit was created in May 1948, and in December, the 38th Engineer Battalion (Special) became the 8460th Special Weapons Group, with all seven special weapons units under its command. The four Army units were then renamed the 111th, 122d, 133d and 144th Special Weapons Units.[27][28] During the late 1940s the Air Force gradually became the major user of nuclear weapons, and by the end of 1949, it had twelve assembly units, and another three in training, while the Army had only four, and the Navy three, one for each of the three Midway-class carriers.[21]