Military doctors perform the same tasks as civilian doctors, just in a military context. While they may work in field hospitals treating the injured on the front lines, most doctors in the military work at hospitals stateside or in military bases, providing the mundane services typically expected of them, diagnosing illnesses and injuries as well as performing preventative checkups.
Military doctors are always commissioned officers, in addition to being doctors. The Air Force, Army, and Navy all have medical corps which employ doctors in a wide number of specialties, from psychiatry to urology. They work on military bases, aboard aircraft carriers and other ships at sea, and at advanced hospitals like Walter Reed Military Medical Center, where presidents receive medical care. Military doctors can be active duty, or serve in the reserve while working in civilian hospitals. Their day-to-day responsibilities are much like those of civilian doctors, treating patients, diagnosing sicknesses, and prescribing medicine.