Allen became a Lieutenant in a company of Green Mountain Boys, was with Ethan Allen when Ft. Ticonderoga was captured from the British, and with Colonel Warner in Canada. He was appointed a captain in Colonel Herrick's battalion of rangers in July 1777, and distinguished himself at the battle of Bennington. In September of the same year he captured Mt. Defiance by assault, and on the retreat of the enemy from Fort Ticonderoga made fifty of them prisoners. Subsequently, he was made major in the rangers, and showed himself a brave partisan leader. In his later life he was always referred to as Col. Allen.