I got 11 credits going to night school while in the Nav. I could only do this on the Tender, I didn't have enough time on the sub. But, I've heard stories about some who did get degree on sub. The Navy will pay 75% of your college fees, but I think you have to get a C at least; the catch is getting your command to support you getting to the classroom; many won't. I didn't want to take correspond. courses though, I wanted to get the classroom experience, which I eventually did.
ACE gives guidelines for what colleges MAY give you for what you've done in the Navy. Some accredited colleges will give you almost a full degree in Nuclear Technology (Thomas Edison and a couple others) for graduating from the nuclear pipeline, while other colleges won't give you any credit at all. University of Delaware gave me nothing, but I didn't care, I wanted the entire experience of getting a 4 year degree. Some schools will give you some credit, and they will give you some credit for taking CLEP tests, which are FREE in the navy, or they were in the 90s.
My advice is to go to school if you enjoy school and get the experience of going to college. But, if you don't like school, just try to get that piece of paper to help out your job-getting ability. Watch out for the Nuclear Technology Degree; I've heard some places know about it and don't give it the same creedence as other degrees earned in a more traditional manner. But I do think it has a good amount of value. My friend got that degree form New York Regents (now called something else), then went back to school and in 2 years and finished his masters from University of Delaware. He used his experience and that degree to become a financial director for a major nuclear company. So it is recognized by other universities and it does hold SOME water in the industry. Maybe your best bet for degree-value/length of time is to find a good school that will give you some large amount of credit hours torwards a degree in Nuclear Engineering. I see you want a degree in Calc/Edu, but maybe that will change. I bet you could find a school to give you some credits for that, but I don't know much about education credits for being a Navy Instructor. someone else will have to help you there.