Yeah, I forgot to respond to this. The Coast Guard doesn't have an "MOS" for its officers. Enlisted have "ratings" which are their specialties.
This of the Coast Guard as a two track career. One track is "operational" like being on a ship, being a pilot, etc. Generally this is out from behind a desk.
The other track is "staff". My "staff" job in the Coast Guard was as a public affairs officer. My operational tour was as a deck watch officer on a cutter.
The most you direct your career along those paths (by planning and putting in for jobs that work along those tracks), the longer and deeper you go, and the more specialized you become.
Assignment officers will also be able to take note of the path your career takes. If you have afloat tours under your belt, you have a shot at another afloat billet with more responsibility, but if you've never been on a cutter, then you won't have a shot at an Operations Officer billet.
Staff tours are all over the board, but you can think of operational tours along three general communities, ashore (sectors, MSOs etc), afloat (cutters) and aviation (helos and fixed-wing).
There are a few officer billets in the MSRT and the MSSTs.