Which battle was the first major American victory of the Revolutionary War in 1775?

The Battle of Fort Ticonderoga was the first major American victory of the Revolutionary War in 1775.

On May 10, 1775, Ethan Allen and the Green Mountain Boys, joined by Benedict Arnold, captured the British-held fort at Ticonderoga in present-day New York. The small garrison surrendered without a major fight, but the victory gave the Patriots control of a strategically important position on the route between Lake Champlain and the Hudson River.

The captured fort also contained heavy cannon. Henry Knox later transported many of those guns to Boston in the winter of 1775–1776. Their placement on Dorchester Heights helped George Washington force the British evacuation of Boston in March 1776.

Fort Ticonderoga was not the opening clash of the Revolution: fighting had already begun at Lexington and Concord in April 1775. Its capture mattered because it supplied weapons and demonstrated that Patriot forces could seize a major British installation.