If you are on active duty, in one of the military academies, or the ROTC, and want 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.