wrote:

If a Marine pilot gets accepted to medical school, and wants to go and
come back into the NAVY as a doctor, how does he go about doing that?

Talk to your recruiter - or career planner if you are a currently
serving Marine aviator.

Can you just transfer from the Marines to the Navy?

With the agreement of both services, yes; but it is pretty much a
case-by-case basis, and remaining post-commissioning/post
flight-school service obligations will probably have to be satisfied
before such a transfer would be approved.

And will they let you leave for Med School

Once your post-commissioning/post flight-school service obligations
are satisfied. Although it is possible that the Armed Forces Medical
University/School/whatever may be a special case. But your recruiter
- or career planner if you are a currently serving Marine, can
probably put you onto the straight dope on this.

or do you have to serve your 8 year aviation
commitment as a pilot?

Generally, if a military service has trained you to fly, your
post-flight school service obligation to that service must be
satisfied before you are free to move on to other things, whatever
they might be.

Thanks in advance! (I'm trying to figure my options out.)

If the Marines send you to flight school and you get your wings, there
is pretty much only one way to get out of serving whatever the service
obligation is at the time you are winged. Screw up badly enough to
not only loose your wings, but to get kicked out of the service or be
"encouraged" to ask to resign your commission. That would probably
put the kibosh on any transfer/move into the Navy as a Doctor, or
anything else for that matter.

OJ III