USUHS is a military medical school for all three branches of the service that is located in Bethesda, Maryland. The undergraduate takes the MCAT, submits an application and goes through an interview process just like with any civilian medical school. USUHS students wear a uniform and get paid an active duty salary as an O1. They make more money than a HPSP student who receives only a stipend. The big difference between USUHS and HPSP is the time commitment. The USUHS graduate owes 7 years active duty time instead of 4.
USUHS is rumored to be more kind to non-traditional applicants such as prior enlisted or military officers looking to become a physician during the application process.
There are also rumors that USUHS graduates get priority over HPSP graduates on the JSGMESB. This is not the case.
If you are on active duty, in one of the military academies, or the ROTC, and want to apply for admission to USUHS a Letter of Approval (LOA) must be obtained from your branch of service. Unless otherwise specified in the LOA the applicant must enter the same component they currently serve in. For example, if you are in the Navy you won't be able to change to the Air Force when you are accepted to USUHS. For those in the reserves, a letter from your commanding officer (who has the authority to release you) will suffice for the LOA. Those in the IRR do not need the LOA.