In 1774, the portion of the 18th in Philadelphia marched across New Jersey to New York, then boarded transports for Boston. In this city Keaton and his comrades saw the outbreak of hostilities and the devastating battle of Bunker Hill. At the end of that year orders were given for the able-bodied men of the 18th Regiment in Boston to be drafted into other regiments; William Keaton transferred into the 43rd Regiment of Foot.
Boston was evacuated in March 1776 and the army regrouped in Halifax, Nova Scotia. The men of the 43rd and the rest of the army spent two months practicing new tactics and field maneuvers in the countryside around Halifax in preparation for a new campaign. By July they were landed on Staten Island; the 43rd was now part of the 5th Brigade of Sir William Howe's powerful army, along with the 22nd, 54th and 63rd Regiments. After a whirlwind Autumn campaign that secured New York city and the surrounding regions, the 5th Brigade was part of a force that landed in Rhode Island in early December.
Rhode Island was the home of the 43rd Regiment for the next three years. While a garrison in strict terms, the island in Narragansett Bay was an active theater of war. Besides being the site of major fighting during August 1778 there were countless incursions and skirmishes throughout the period. Soldiers manned guard posts day and night year round, ever vigilant for the next American attempt to harass or unseat the garrison.
When Rhode Island was evacuated in October 1779, Keaton and the 43rd returned to the New York area where they spent the following year in a relatively calm garrison. 1781, however, saw them on campaign again, this time sailing to Virginia. Sent to reinforce Cornwallis' army, they arrived on the banks of the James River in the late Spring. By August they were part of the substantial army establishing a post around Yorktown.
William Keaton had spent 14 years marching, sailing, working and fighting all over the American colonies. He had seen the wilderness with the 18th Regiment and several significant battles with the 43rd, and had certainly lost many comrades along the way. Now he was helping to lay the groundwork for the action that would effectively end the war, but he would not see this dramatic culmination. In in hot Virginia weather of early August the hazards of military campaigning caught up to him. On either the 7th or the 9th, depending upon which source is accurate, thunderstorms pelted the area. William Keaton was struck and killed by lightning, as was a soldier's wife in the 43rd and a soldier of the Queen's Rangers.