The Siege of Boston (April 19, 1775 – March 17, 1776) was the opening phase of the American Revolutionary War, in which New England militiamen—who later became part of the Continental Army—surrounded the town of Boston, Massachusetts, to prevent movement by the British Army garrisoned within. The Americans, led by George Washington, eventually forced the British to withdraw from the town after an 11-month siege.
The siege began on April 19 after the Battles of Lexington and Concord, when the militia from many Massachusetts communities surrounded Boston and blocked land access to the then-peninsular town, limiting British resupply to naval operations. The Continental Congress chose to adopt the militia and form the Continental Army, and unanimously elected George Washington as its Commander in Chief. In June 1775, the British seized Bunker and Breeds Hills, but the casualties they suffered were so heavy and their gains were insufficient to break the siege. For the rest of the siege, there was little action other than occasional raids, minor skirmishes, and sniper fire. Both sides had to deal with resource supply and personnel issues over the course of the siege, and engaged in naval operations in the contest for resources.
In November 1775, Washington sent a 25 year-old bookseller-turned-soldier named Henry Knox to bring heavy artillery that had been captured at Fort Ticonderoga to Boston. In a technically complex and demanding operation, Knox brought many cannons to the Boston area in January 1776. In March 1776, these artillery were used to fortify Dorchester Heights, overlooking Boston and its harbor and threatening the British naval supply lifeline. The British commander William Howe, realizing he could no longer hold the town, chose to evacuate it. He withdrew the British forces, departing on March 17 (celebrated today as Evacuation Day) for Halifax, Nova Scotia.
Between November 1775 and February 1776, Colonel Henry Knox and a team of engineers used sledges to retrieve 60 tons of heavy artillery that had been captured at Fort Ticonderoga. Bringing them across the frozen Hudson and Connecticut rivers in a technically challenging and complex operation, they arrived back at Cambridge on January 24, 1776.
Some of the Ticonderoga cannons, which were of a size and range not previously available to the Americans, were emplaced in fortifications around the city, and on the night of March 2, the Americans began to bombard the city with those cannon, to which the British responded with cannonades of their own. The American guns, under the direction of Colonel Knox, continued to exchange fire with the British until March 4. The exchange of fire did little damage to either side, although it did damage houses and kill some British soldiers in Boston. On March 5, Washington moved more of the Ticonderoga cannon and several thousand men overnight to occupy Dorchester Heights, overlooking Boston. Since it was winter the ground was frozen, making the digging of trenches impractical. Washington's men instead used logs, branches and anything else available to fortify the position overnight. General Howe is said to have exclaimed, "My God, these fellows have done more work in one night than I could make my army do in three months." The British fleet was within range of the American guns on Dorchester Heights, putting it and the troops in the city at risk.
The immediate response of the British was a two hour cannon barrage at the heights, which had no effect because the British guns could not reach the American guns at such height. After the failure of the barrage, Howe and his officers agreed that the colonists must be removed from the heights if they were to hold Boston. They planned an assault on the heights; however, due to a storm the attack never took place, and the British elected instead to withdraw.
On March 8, some prominent Bostonians sent a letter to Washington, stating that the British would not destroy the town if they were allowed to depart unmolested. Washington was given the letter, but formally rejected it, as it was not addressed to him by either name or title. However, the letter had the intended effect: when the evacuation began, there was no American fire to hinder the British departure. On March 9, after seeing movement on Nook's Hill on Dorchester, the British opened a massive fire barrage that lasted all night. It killed four men with one cannonball, but that was all the damage that was done. The next day, the colonists went out and collected the 700 cannonballs that had been fired at them.
On March 10, General Howe issued a proclamation ordering the inhabitants to give up all linen and woolen goods that could be used by the colonists to continue the war. A Loyalist, Crean Brush, was authorized to receive these goods, in return for which he gave certificates that were effectively worthless. Over the next week, the British fleet sat in Boston harbor waiting for favorable winds, while Loyalists and British soldiers were loaded onto the ships. During this time, American naval activities outside the harbor successfully captured and diverted to ports under colonial control several British supply ships. On March 15, the wind became favorable, but before they could leave, it turned against them. On March 17 the wind once again turned favorable. The troops, who were authorized to burn the town if there were any disturbances while they were marching to their ships, began to move out at 4:00 a.m. By 9:00 a.m., all ships were underway. The fleet departing from Boston included 120 ships, with more than 11,000 people aboard. Of those, 9,906 were British troops, 667 were women, and 553 were children