Numbers were different series for different services and times, and from what locations, et. Mine was from Atlanta Ponce DeLeon Induction Center in May of 1968 Airforce.......
6 months they changed it from AF127890XX to an FR(my social security number).
Ah, Ponce Induction center. now there’s a memory.
Next stop PI.
If it had been, you'd likely have joined during WWII..
Sadly, both of my uncles and my father served in the Army Air Forces in WWII and they developed a rather loftily superior attitude when dealing with me - one of uncles said that "anybody who's dumb enough to join the Marines during a war is an idiot".
It was quite a while until he and I spoke again.