The Army can reassign you to wherever they need you, if necessary, even if it isn’t what you enlisted for. Also, most functions the enlistee knows off the bat that Chillul Shabbos (and a host of other aveiros) is a near certainty.
They can, but that doesn’t mean that they routinely do so willy-nilly.
In any event, I would advise you to ask your LOR before making such absolute pronouncements… especially considering the fact that there *are* frum yidden in the armed forces (including chaplains) and they may well have asked and been told it was muttar before enlisting.
The Wolf