. Following the outbreak of the American Revolutionary War, Caldwell again served under Dunmore at the
Burning of Norfolk in January 1776. He was injured during this engagement and evacuated to New York. After recovering from his wounds, Caldwell went to
Fort Niagara, where he joined the
British Indian Department. He was present at the
Siege of Fort Stanwix in August 1777. Caldwell transferred to Butler's Rangers upon its formation later that year. He was commissioned a captain on 24 December 1777 and given command of a
company. Caldwell was in the field for most of the war and spent very little time at Fort Niagara except when ill or wounded. On 3 July 1778, Caldwell led his company at the
Battle of Wyoming. Under the command of Major
John Butler, the Rangers and their
Iroquois allies routed the Patriot militia who had marched out to attack them. The battle is often referred to as the "Wyoming Massacre" because of the roughly 300 Patriot casualties, many of whom were killed by the Iroquois as they fled the battlefield or after they had been taken prisoner. Widespread looting and burning of buildings occurred throughout the
Wyoming Valley in the days following the battle, but non-combatants were not harmed. In September 1778, Caldwell was with Brant during the
attack on German Flatts in the
Mohawk River valley. The settlers received timely warning of the attack, and took refuge inside
Fort Herkimer and
Fort Dayton. Brant and Caldwell destroyed 63 homes in the vicinity, a similar number of barns, three grist mills, and one saw mill. They drove off a large number of horses, cattle, and sheep, killing those they could not take with them. More than 700 people were made homeless. Because they had been forewarned only three settlers were killed. Caldwell wrote that the attack, "would have in all probability killed most of the inhabitants of German Flatts had they not been apprised of our coming by one of the scouts getting in and warning of our approach." In November 1778, Caldwell was with the expedition commanded by Captain
Walter Butler that raided
Cherry Valley. Although the settlement was defended by a fort garrisoned by the
7th Massachusetts Regiment, many of the officers were billeted in homes some distance away, including their commanding officer. Butler deployed the two companies of Rangers and a detachment of British regulars against the fort but failed to restrain his
Seneca allies who rampaged through the settlement. 14 soldiers and 30 non-combatants including women and children were massacred and another 70 taken prisoner. In October 1780, Caldwell was part of the large-scale raid against the
Schoharie and Mohawk River valleys of New York that culminated in the inconclusive
Battle of Klock's Field. In August 1781, he led the raid that burned mills, storehouses and barns at
Wawarsing and
Napanoch in
Ulster County, New York. In his report to Powell, Caldwell wrote, "I had the good fortune not to have a Ranger killed or wounded during our operations in those settlements." He ended his report with, "It is almost impossible to describe the situation of the party at present, worn out with hunger and fatigue." Caldwell was posted to Detroit in October 1781 and remained there for the remainder of the war. In June 1782, he led his company and Indigenous allies during the opening stages of the
Battle of Upper Sandusky. Caldwell was wounded in both legs early in the engagement and turned over command to
Matthew Elliot, a British Indian Department officer. Two months later, Caldwell and 300 Indigenous warriors briefly besieged
Bryan Station then routed the Kentucky militia at the
Battle of Blue Licks. ==Postwar==