Gore graduated in 1776, and promptly enlisted in the Continental artillery regiment of his brother-in-law Thomas Crafts, where he served as a clerk until 1778. The Gore family was divided by the war: Gore's father was a Loyalist who left Boston when the British Army evacuated the city in March 1776. Gore was consequently called upon to support his mother and three sisters, who remained in Boston. In 1779, Gore successfully petitioned the state for the remaining family's share of his father's seized assets.