No, I am not talking about being a GMO. The Army and the Air Force have pretty much gotten rid of GMOs. The Air Force is even limiting people who are flight docs as GMOs. They have realized that you are much more valuable to them as a board certified physician than as a GMO. However, the Navy still uses them. I have virtually no worry about becoming a GMO. Most people who become a GMO in the Air Force are people trying to accrue board points for a super-competitive residency.
All three of the services have residency programs similar to their civilian counterparts. The Joint Graduate Medical Education Board meets the week after Thanksgiving each year to assign applicants to those positions in all three services.
So what are these positions? Each spring the medical powers-that-be in the Air Force meet and determine how many physicians of each specialty will be needed when that year group completes its training. There are a set number of positions at the military training programs, so the rest are deferred positions. The Air Force is unique in that, unlike the Army and Navy, they only have about half the residency positions it needs to train its physicians, and consequently has the highest number of deferred positions.