pgg, don't they also, to some extent, dictate what specialty you are "allowed" to go into? I know that some years, people who wanted to do anesthesiology were not allowed to due to the numbers game.
loveoforganic2 is basically right.
No branch of the military can force anyone to do a residency they don't want to do. At worst, if you apply and don't match to your desired specialty, you can serve out the remaining years of your payback as a GMO (general medical officer), get out, and go do a residency like a normal civilian. The life of a GMO is mostly primary care / operational medicine directly attached to some line unit. In the Navy that usually means being the doc for a Marine unit, or air wing, or ship ... many variations.
The big risk with getting the military residency you want is year-to-year volatility and skewed competitiveness compared to the civilian match. It's a much smaller pool of applicants chasing a much smaller number of positions. For example, I think the Navy currently has just 14 or 15 CA1 positions open each year. If there are 20 people chasing those spots one year, there might be 30 applicants the next. Sometimes this works in the applicant's favor, sometimes it doesn't. Usually EM is far more difficult to match to in the military than outside ... but on the flip side more competitive specialties like radiology, ophtho, neurosurg, etc often have years where it's less competitive.
For the most part, it works out, and most people get what they want. Even in the military, high quality applicants typically get what they want, eventually. However, almost every Navy applicant who wants a non-primary-care residency will spend 2-3 years as a GMO before being competitive for an inservice residency. This is the source of a lot of hate and discontent because
1) It's a 2-3 year delay before desired specialty training. The medical practice is admin heavy and not very interesting. It delays a pay raise. Very high deployment rate during this period.
2) GMO time counts as payback ... but residency incurs a new concurrent obligation. So if you do your GMO time and then hit residency, you may find yourself exiting residency owing more time than you did in the first place. Before you know it, that promised 4-year HPSP payback has morphed into 8 or 10 years of active duty after med school.
GMOs exist in the Army and Air Force too, but continuous contracts for internship+residency are the norm in those services. (The flip side to that "advantage" is that they fill their operational billets with residency-trained physicians ... meaning that there are people who finish their _____ residencies/fellowships only to find themselves parked at an infantry regiment for a year or two, not really practicing _____. No free lunch.)
Those who pay back their 4 years as a GMO and get out, and apply for civilian residency spot, almost universally do well. Most programs look upon ex-military people very favorably, from what I understand.
Bottom line, and this maybe sounds a little bit of an oversimplification and/or statement of the obvious ... Debt aversion is great, but people shouldn't join the military via HPSP for the money. They should join the military via HPSP because they want to be in the military.
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Edit to add one more comment to this -
pgg, don't they also, to some extent, dictate what specialty you are "allowed" to go into?
There are some specialties that simply aren't
needed in large numbers in the military. If you're interested in some odd subspecialty, it may be nearly impossible to get there while in the military. There are "war critical specialties" that will always be well-represented in the military, and to a lesser extent "dependent/retiree specialties" that will
probably continue to be well represented, but we we just don't need a lot of pediatric oncologists.
This is an added risk to taking HPSP. Most pre-meds have an idea of what specialty they want to go into, and most of them change their minds. If you joined thinking family med was your future, but now you're an MS3, 3 years into taking HPSP money, and you do a rotation and fall in love with _____ obscure specialty, you may be locking yourself into the "do my 4 years as a GMO and get out to do residency" path.