The word bandied about at the local Navy Base among members of the "Silent Service" is subMARiner which I used when amongst them, however for the civilian population it's subMARINers

It looks like I have been guilty of unwarranted extrapolation. I watched a documentary in which a retired USN admiral, formerly head of the USN's submarine fleet, consistently said submarine-r. Since he had formerly been one, I leaped to the contusion that all USN submariners pronounced it the way their former boss did. Whoops!