About 700 British Army regulars, under Lieutenant Colonel Francis Smith, were given secret orders to capture and destroy military supplies that were reportedly stored by the Massachusetts militia at Concord. Through effective intelligence gathering, Patriot colonials had received word weeks before the expedition that their supplies might be at risk and had moved most of them to other locations. They also received details about British plans on the night before the battle and were able to rapidly notify the area militias of the enemy movement.

The first shots were fired just as the sun was rising at Lexington. The militia were outnumbered and fell back, and the regulars proceeded on to Concord, where they searched for the supplies. At the North Bridge in Concord, approximately 500 militiamen fought and defeated three companies of the King's troops. The outnumbered regulars fell back from the minutemen after a pitched battle in open territory.

More militiamen arrived soon thereafter and inflicted heavy damage on the regulars as they marched back towards Boston. Upon returning to Lexington, Smith's expedition was rescued by reinforcements under Lieutenant-General Hugh Percy. The combined force, now of about 1,700 men, marched back to Boston under heavy fire in a tactical withdrawal and eventually reached the safety of Charlestown. The accumulated militias blockaded the narrow land accesses to Charlestown and Boston, starting the Siege of Boston.

Was the order passed along the front lines of the militiamen as the British troops moved toward them. When that moment came, the word "FIRE!" was shouted, and whole enemy platoons were mowed down and shattered, retreating to the foot of the hill.

In all of the twenty battles of the Revolution, Bunker Hill exacted a heavy toll on British officers. In this one battle alone one-eighth of the British officers in the entire War were killed and one-sixth were wounded on that day.

Following the earlier skirmishes at Lexington and Concord, the battle of Bunker Hill was significant in that it overruled any real hope of conciliation. The outcome of the battle rallied the colonies and moved a lethargic Congress to take action. Bunker Hill showed the Americans that the British were not invincible. It showed the British Government that the "rebels" were a serious opponent, that "the mightiest army in all of Europe" had a real fight on its hands.