It's not for everybody, but for many, the military is the best way to pursue medical training and/or practice their medical career. 

Medical personnel, both officers and enlisted, are found in the Air Force, Army, and Navy.  Navy medical personnel support the Marines.  While it isn't a military force, the U.S. Public Health Service is a uniformed service as well. 

Generally, to enter the military you must be between 17 and 35 years old, be in good health, be a citizen or legal alien, and have good moral character.  If you are joining as an enlisted person, you must achieve a minimum score on the Armed Services Vocational Aptitude Battery (ASVAB).  Depending upon their ASVAB performance and record enlisted personnel may sign-up for specialized medical technical training.  For more information on enlisting in a medical field, visit a local recruiting office. 

Medical professionals may receive direct commissions as officers, but most medical officers enter through the Reserve Officers Training Corps (ROTC), the Armed Forces Health Professions Scholarship Program, or the Uniformed Services University of the Health Sciences. 

ROTC offers non-need based scholarships to undergraduates in return for a post-graduation service committment.  This committment can be delayed to complete a medically related graduate or professional degree.  The Army has a special Nursing ROTC program. 

The Armed Forces Health Professions Scholarship Program (Air Force, Army, and Navy) provides scholarships for dental, optometry, medical, osteopathic, and nurse anesthesia students.  Scholarship benefits include full tuition and fees, reimbursement books and supplies, monthly stipends, and 45 days of active duty each academic year for military training.  Of course, you must serve on active duty after your graduate.  If you're really interested, you can view the Army's handbook for HPSP students. 

The Uniformed Services University of Health Sciences is a fully accredited medical school. There is no tuition, and books and supplies are provided free of charge.  Students receive commissions as Ensigns (Navy and Public Health Service) or Second Lieutenants (Air Force and Army) when they enroll and receive full pay and allowances while attending classes.  Upon graduation they are promoted to Lieutenants (Navy and Public Health Service) or Captains (Air Force and Army) and serve an internship at a military hospital.