Every boat carries at least 3 MA's (2 at sea, 1 left inboard (called 5th watch), who rotate with all 3 onboard alongside).
The only ones who don't go to sea are CPOMA(SM)s, unless there's a critical shortage of POs, so you'll crack in a fair bit of seatime before you reach the dizzy heights of Chief, although the CPOMA(SM) on FOST staff gets a few sea rides during a boats workup period.