My cousin served more than a decade on nuclear subs and he is one of the least yogi/monk like people I’ve met. Virtually no one who knows him would say he exhibits lots of self control.

He just isn’t bothered by tight spaces or being underwater and he liked the regimented life the navy provided because it made up for his own lack of internal discipline.

I don’t know if he is normal or not on submarines but you certainly don’t have to be some guru to serve on them.