To reiterate:
Told by whom? Did you ask to see the instruction stating that NROTC MIDN had to put nuke down on the service select? As far as the service select guys are concerned you requested nuke. It may not have been your first choice, but it was on the request sheet nonetheless. The minute you wrote that in, you volunteered for sub duty.
Like I said, I am sympathetic to the fact that it's tough to take a stand in such a situation when you think it'll end up getting you in trouble, but that's something you have to learn to do if you know you are in the right. Instead, you thought that you'll just comply and it'll be okay because they won't possibly pass you over for 3 other choices to get all the way to nuke, right? Much easier to just rely on that chance and bitch about it later.
He's not lying. I saw the selection sheet for the current seniors when I was stashed. It said your requests wouldn't be considered complete unless males had subs somewhere on there and females had nuke SWO. Furthermore, to prevent the SWO and go types from stacking their selections, only one SWO option could be listed in the top 3; if they wanted more that one SWO option on there it could only go in the 4/5 slots.