In 1774, when Massachusetts towns began forming militia companies, Prescott was commissioned to command a company and laid siege to Boston after the Battle of Concord. Prescott was then chosen to lead 1,200 men onto the Charlestown peninsula and erect defenses on Bunker Hill on the night of June 16, 1775. Prescott is credited with uttering, "Do not fire until you see the whites of their eyes", so that the colonial troops could shoot more accurately and so conserve their limited stocks of ammunition. Prescott's men twice threw back British assaults on the redoubt but when the British made a third attempt on the ammunition-less forces, he ordered a retreat while parrying bayonet thrusts with his ceremonial saber. While the British successfully captured Bunker Hill, the poorly organized and untrained colonial forces inflicted significant casualties (50% casualties under General Howe), and the British were unable to capitalize their victory. Prescott received a colonel's commission, and his unit became the 7th Continental Regiment. The regiment saw service in the 1776 defense of New York.