There are multiple pathways to do military medicine.
Probably the most direct is through USU, which covers everything, and you are active duty at the time. This commiement is commonly understood as 7 years active plus 8 years reserve.
www.usuhs.edu
Then there are various scholarships that you obtain once you are accepted into medical school, such as HPSP, HPCP. These typically are 4 year commitment scholarships, but can vary based on when you get them. Talking to any recruiter of any branch can give you more information as well.
Learn more about the military medical school scholarships that are available through the Health Professions Scholarship Program (HPSP).
www.medicineandthemilitary.com
www.airforcemedicine.af.mil
Navy Health Services Collegiate Program (HSCP) is a scholarship program designed to provide financial incentives for students in designated health care professions.
www.navycs.com
Finally, there a plethora of ways in after/during residency, such as FAP. All of these pathways are discussed in the link below. I think this blog is one of the best in the military. Schofer is a concientious updater of information.
Posts about FAP written by Joel Schofer, MD, MBA, CPE
mccareer.org
If you have questions about a specific pathway, let us know.