The American Revolutionary War broke out with the April 1775 Battles of Lexington and Concord. In early May, the legislature of Rhode Island established the Rhode Island Army of Observation and appointed Greene to command it. Greene's army marched to Boston, where other colonial forces were laying siege to a British garrison. He missed the June 1775 Battle of Bunker Hill because he was visiting Rhode Island at the time, but he returned almost immediately after the battle and was impressed by the performance of colonial forces. That same month, the Second Continental Congress established the Continental Army and appointed George Washington to command all colonial forces. In addition to Washington, Congress appointed sixteen generals, and Greene was appointed as a brigadier general in the Continental Army. Washington took command of the Siege of Boston in July 1775, bringing with him generals such as Charles Lee, Horatio Gates, and Thomas Mifflin. Washington organized the Continental Army into three divisions, each consisting of regiments from different colonies, and Greene was given command of a brigade consisting of seven regiments. The Siege of Boston continued until March 1776, when British forces evacuated from the city. After the end of the siege, Greene briefly served as the commander of military forces in Boston, but he rejoined Washington's army in April 1776.