We now have available copies of the official “after action” reports submitted to Royal Governor-General Thomas Gage and the Parliament in London by British Brigadier General Hugh Percy, his subordinate officers, Lieutenant Colonel Francis Smith, commanding the 10th Regiment of Foot [infantry], and Major John Pitcairn commanding the Royal Marine Detachment.

Colonial Militia leaders and militiamen present during the engagements of 19 April 1775 also provided contemporaneous depositions to the Massachusetts Provincial Congress. British and American accounts differ as to numbers involved and the question of who fired the first “shot heard ’round the world.”

The American narratives credit the secret “Alarm and Muster Network,” in which Paul Revere, William Dawes, and Samuel Prescott served to be crucial in alerting local militiamen to the British expedition. The courage and tenacity of these messengers on the night of 18–19 April saved John Hancock and Samuel Adams from capture and resulted in nearly 4,000 armed militiamen and “Minutemen” rushing to Lexington, Concord, and engaging the British Regulars on their retreat to Boston.

A review of the surviving records yields a “best estimate” of these events as follows:

Only seventy-seven militiamen were assembled on the green in Lexington when the lead elements of 700 British Regulars and Marines arrived at the town just after sunrise on 19 April 1775. After a brief skirmish, during which eight of the militiamen were killed and a dozen were wounded, the outnumbered Patriots dispersed and 400 British troops [Regulars and Marines] proceeded to Concord with the mission of seizing colonial munitions—weapons, powder, and shot—and capturing John Hancock and Samuel Adams.

In Concord, and at the two bridges north and south of town, 375–400 militiamen initially engaged the British Regulars and Marines with minor effect. But as the day progressed, nearly 4,000 Patriot militiamen and Minutemen reinforcements arrived to fight the British during their retreat.

British search parties found small quantities of gunpowder, lead shot, a few muskets, two heavy siege cannons, and gun carriages in Concord and the surrounding farms. The Regulars set fire to most of this “war material” and battered the trunnions off the cannons with sledgehammers, rendering the artillery pieces unusable.

Shortly after noon, the King’s troops, exhausted from marching through the previous night and the skirmishes in Lexington and Concord, set out on the seventeen-mile return hike to Boston. For the British, it was an unmitigated disaster.

From Cambridge, Brigadier General Percy sent forward another 1,000 Regulars as reinforcements but the British were still outnumbered by more than two to one and constantly fired upon from their flanks and rear throughout the retreat to Boston. By the time the British finally reached Charlestown on the outskirts of Boston at dawn on 20 April, seventy-three British Regulars were dead [including twenty-eight officers], 175 were wounded, and fifty-three were MIA.

Among the 3,971 Patriot Militia and Minutemen engaged in the fight, forty-nine were killed, forty-one wounded, and four were MIA. By noon on 20 April 1775, the siege of Boston was underway and the American Revolution had begun.