So, will he still be a "nuke"?

Is this just a normal step in the process or did he somehow lose the chance? When I was in the army, I went from basic training to AIT, which is where I learned to be an avionics technician. That was my MOS. There was nothing after that except duty stations and extra training as new equipment was introduced to the army. If the navy is comparable, then my son goes to basic, then to training as either a "nuke" guy (as originally planned) or to be an EM (as it may be now). After nuke school OR EM school, he would be a "nuke" or an EM, depending on which of the two schools he goes to. If it were the same as the army, that would be it. One or the other, except with the possibility or re-training which often, in the army, comes at re-enlistment. I'm just wondering how the navy might be different.

I realize sometimes people fail tests, etc. during training and have to be assigned to a different field or booted out altogether, but I can't see how anything in basic training would call for that. Personally, I was approached in basic training, because of my ASVAB score and security clearance, about a special opportunity in military intelligence, which I turned down. But that's all I could see happening as far as changing your job while still in basic training.
Thanks.

yeah, all except the part about him being presumed dead.