I am not a corpsman and I never served as one but as a retired naval officer, I had occasion to work with and be cared for by many corpsman. One even saved my life a long time ago.
Corpsman is a great rate in the Navy. It is a rate that can and does serve in virtually every type of unit such as all surface ships, air squadrons, submarines, USMC infantry companies and to the Fleet headquarters. They serve ashore at virtually every single Navy/Marine Corps shore facility around the world and at all Navy clinics and hospitals around the world. Wherever the Navy goes, you will find Corpmen. (The Marines, as part of the Dept. of the Navy, don't have their own medics.)
Corpsmen work as X-ray techs, surgical assistants, field medics for the grunts, neo-natal (new baby) techs in hospitals and...well the list goes on forever.
Senior corpsmen often go through extended training and are detailed to a destroyer, cruiser or sub. There is no medical officer (doctor) normally assigned to small commands like these, so the "Doc" is the only one aboard to take care of all 300 or so men and women. He/she usually has a junior corpsman as an assistant.
If you stay a full 20 years to retirement, you can expect at least one tour with the Fleet Marine Force (FMF). During this difficult and rewarding tour, you will by driven hard to stay up with the Grunts...which you WILL; and you will be highly regarded and respected. The Grunts do like their Docs. Plan on learning to shoot too...shotgun, M-16/M-4 or maybe an M-9 (Ugh!). I know of no FMF Corpman who went into the bush unarmed.
Oh...and most of the Navy enlisted Medal of Honor awardees have been Corpsmen.
Good Luck!