There vast majority of the US Navy are US citizens. It is not a requirement that you be a citizen, but it does have restrictions. A non-citizen cannot obtain a security clearance. This would prevent...
There are currently 14 Ohio-class boomers still performing strategic deterrence patrols; 4 others were converted to SSGN's.
You contact your local recruiter, and they'll run you through the specifics. Simply talking to a recruiter does not obligate you to join the military.
the US navy developed ROV in the 1960s and it was developed because the navy was responsible for the ROV technology!
The 7th Fleet did most of the gunline work along the coast.