Three other thoughts (me being an IM outsider):
1. For IM subspecialties, the pandemic hit their patient referrals and census hard. While COVID shut nearly everyone down, the DOD hospitals seem to have been even slower to recover. A lot of nurses were lost, especially the DOD contractors. Also, the active duty personnel were sent across the nation (NYC, North Dakota, etc.) for COVID deployment. Then there was the Afghan refugee crisis... Meanwhile, the home stations suffered. Concrete examples: Heme/Onc was only treating active duty soldiers/airmen, *not even their spouses*. I have no idea how their fellowship fared, but it felt like the patients were being sent out into a void (and weird stuff can happen in the outside). Gastroenterology also suffered- scope numbers plummeted. Even after COVID restrictions were lifted, GI didn't recover due to lack of staffing. I quit scoping due to the chaos. While is COVID is over, any national 'emergency' can affect the military staff and hospitals.
2. DHA realignment seems to hit IM particularly hard. There are some with more knowledge on this topic, but DHA wants to emphasize physicians who deploy, e.g. surgeons. They ravaged pediatrics and gyn, and I think IM (e.g. nephrology) allocation also got hit. While you may want to be a true generalist / hospitalist, your mind could easily change. And if the subspecialists are suffering, that means your training rotations suffer. They will try to satisfy ACGME, but they may have to duct tape together outside rotations.
3. Deployments for IM are generally awful. That's mainly an outpatient GP / brigade surgeon / flight surgeon gig. Deployment IM consists of musculoskeletal injuries, STDs, and a morass of URTIs with malingering. In the midst of this, bet on one true zebra which will be mind boggling, and generally the service member will suffer and be flown out, and then the Monday-morning-quarterbacking will begin. In wartime, rheumatologists are sent to Forward Operating Bases to be family med, and hospitalists at the Role III are serving as trauma surgery residents / PAs, i.e. ward monkeys. Some of them are understandably ticked because the trauma czar wants them to be fluent in trauma care. Occasionally, there will be a legit MI, and if the cardiologist is around, they will shrug their shoulders, consider heparin, and try to evac the patient ASAP. Then the cardiologist will return to the ward to write progress notes. If you're not busy, then they'll try to hook you into command or policy making (COVID was really bad for this). Maybe you would like it, but most doctors don't.
3*. Once again, if you're not busy, even at your home station, they may turn you into a bureaucrat / commander. Writing officer performance evals, public health stuff, disease prevention, educating personnel beyond their scope of practice (less onerous but gets tiring), teaching ACLS, etc.
Yeah... I wouldn't do IM... I would just do Family Practice..