Varnum marched the regiment to Roxbury, Massachusetts in June 1775, where it took part in the siege of Boston as part of the Army of Observation. It was adopted into the Continental Army by act of Congress on 14 June 1775. It was expanded to ten companies on 28 June, and was assigned to General Nathanael Greene's Brigade in General George Washington's Main Army on 28 July. General Washington officially took command of the Continental Army upon his arrival in Cambridge, Massachusetts on 3 July 1775.