Following his exciting electoral victory, Colonel Campbell left his elder brother, Sir James Campbell (1737–1805) of Killean, to keep his parliamentary seat warm and sailed for America in command of the
71st Regiment of Foot, Fraser's Highlanders, where the
American Revolutionary War was in progress. In 1776, after a battle aboard a vessel in
Boston Harbor, Campbell was captured by the Americans and held prisoner until 1778. Campbell's capture coincided with the British capture of the American military officers
Ethan Allen and General
Charles Lee. Rumours spread among the Americans that Allen and Lee were being mistreated in British captivity, which led Campbell's American captors to torment him. In February 1777, from
Concord Jail, an outraged Campbell complained to
Viscount Howe of his situation. There then ensued complaints and correspondence between Howe and
George Washington on Campbell's behalf. By the following month Washington intervened and
Congress protested that it had not intended to cause undue suffering to Campbell. By May, Campbell was living at the jailer's tavern, a marked improvement to his previous solitary confinement. Soon afterwards he was granted total freedom within the confine of the town of Concord, and during these years as a
prisoner of war he was able to purchase the Knap estate back in
Argyll. On 6 May 1778, he was finally
released in exchange for Ethan Allen. ==Battle of Savannah and Governor of Georgia==