Knox was active in the Massachusetts militia and joined the Continental Army in 1775 at the outbreak of the Revolutionary War. During the winter of 1775–76, he transported cannons, mortars, and howitzers using sleds, some 300 miles from Fort Ticonderoga to Boston. Knox, then a brigadier general, capably commanded artillery at the Battle of Monmouth in the Philadelphia Campaign of 1778, and ultimately directed the American artillery at the Siege of Yorktown. Knox succeeded George Washington as commander of the Continental Army in December 1783, and a few years later was appointed secretary of war.