Federal officials reviewed the work of Major Jonathan Letterman, head of the Army of Potomac’s medical corps, in light of Union casualties suffered at Antietam. General George McClellan had earlier tasked Letterman to improve the efficiency of the Union medical corps. Letterman responded, forming an independent ambulance corps to remove the wounded from the battlefield. Then, at sites off the battlefield a system of triage—determining casualties as lightly wounded, severely wounded, or fatally wounded—would be used.
At Antietam, nearly 10,000 Union troops were wounded in a single day, and all were carried from the field and cared for within 24 hours. Letterman’s emergency care procedures would become standard operating procedure for the U.S. Army, saving countless soldiers’ lives.