American military doctors are basically hired from local professionals.
The army itself has trained a small number of military doctors. If you want to become a military doctor, you must first complete a bachelor's degree education. The US military calls it pre-medical education, which lasts for 4-5 years. After passing the exam, I was admitted to medical university, which is a four-year medical education stage. After graduation, you will receive a long post-graduation medical education for medical students. At this stage, you are not a formal military doctor, and you are not qualified to practice. You are a trainee military doctor. Take the United States Navy as an example. Trainee military doctors who have studied for 8-9 years should practice in grass-roots combat troops for one year, and then go back to school to participate in medical education after graduation. It is equivalent to the postgraduate stage of medical students.
The fourth stage is on-the-job lifelong vocational education for military doctors, that is, military doctors who have officially obtained the qualification of practicing doctors. After completing this stage of study, most American military doctors are doctors.