The Medical Department of the United States Army, much like the rest of the military service, was caught unprepared at the start of the Civil War. Under its aging leader, Thomas Lawson, the department was understaffed, undersupplied, and barely capable of tending to the needs of the army in peacetime. At the war's beginning, fewer than 100 doctors were employed, and the department was short of medical instruments, medicines, even thermometers and bandages. The shortage of trained doctors worsened when more than one-quarter joined the Confederate army or fled to private practice. State examining boards, faced with the need to certify their replacements, passed poorly trained and sometimes completely unqualified candidates in order to fill the quota demanded of each state.

Once they were accepted into service, the army doctors realized they would be dealing with much more than gunshot or bayonet wounds. The...