General George McClellan used the Pry House as the headquarters for the Union Army of the Potomac, where officers placed some of the Pry family furniture on the lawn beside a small redan of fence rails with telescopes mounted, and eyewitnesses recalled the commander watching the battle while reporter Charles Coffin found him there with his staff and their saddled horses nearby. Because the house stood on high ground, it also served as an important signal station, part of a network in which both armies used flags or torches for rapid communication across the battlefield, with the U.S. Signal Corps operating throughout the battle from stations here and on Elk Ridge more than a mile to the east. After the battle, when the Antietam Valley became one vast hospital with more than 18,000 wounded and over one hundred field hospitals in houses, barns, churches, and tents, the Pry home and barn cared for wounded soldiers, chiefly from the Union Second Corps. Joseph Hooker was brought to the house briefly after being wounded near the Cornfield before transfer to Washington, D.C. Israel Richardson, wounded while leading his division at Bloody Lane, was cared for by his wife and sister in an upstairs bedroom for more than a month until he died of his wounds on November 3. During an October visit, President Lincoln came to the Pry House with McClellan and also made a point of seeing Richardson. Jonathan Letterman, medical director for the Union Army of the Potomac, reorganized field medical care and established an ambulance corps first successfully instituted at Antietam, helping bring order to the battle's aftermath.
