When fighting in the American Revolutionary War began, Dearborn fought with the Continental Army as a captain in the 1st and 3rd New Hampshire Regiments; he soon rose to the rank of lieutenant colonel. He was appointed Deputy Quartermaster General in July 1781 and served on George Washington's staff while in Virginia. At age twenty-three, he organized and led a local militia troop of sixty men to the Boston area, where he fought on June 17, 1775, at the Battle of Bunker Hill as a captain in Colonel John Stark's 1st New Hampshire Regiment. During the battle, Dearborn observed that "Not an officer or soldier of the continental troops engaged was in uniform, but were in the plain and ordinary dress of citizens; nor was there an officer on horseback." Dearborn years later would accuse Israel Putnam of failing his duty during that battle, resulting in what has since been known as the Dearborn-Putnam controversy.