Siege of Boston 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 garrison ed within . After eleven months of siege , the American colonists , led by George Washington , forced the British to withdraw by sea . 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 Breed ' s Hills , but the casualties they suffered were 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 pieces 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 . Background . Prior to 1775 , the British had imposed taxes and import duties on the American colonies , to which the colonists objected , since they lacked representation in the British Parliament . In response to the Boston Tea Party and other acts of protest , 4 , 000 British troops under the leadership of General Thomas Gage were sent to occupy the city of Boston and to pacify the restive Province of Massachusetts Bay . Gage , among other actions authorized by Parliament in the so - called " Intolerable Acts " , disbanded the local provincial government ( led by John Hancock and Samuel Adams ) , which reformed itself into a Provincial Congress , and continued to meet . The Provincial Congress called for the organization of local militias and coordinated the accumulation of weapons and other military supplies . Under the terms of the Boston Port Act , Gage closed the Boston port , which caused much unemployment and discontent . When British forces were sent to seize military supplies from the town of Concord on April 19 , 1775 , militia companies from surrounding towns opposed them in the Battles of Lexington and Concord . At Concord , some of the British forces were routed in a confrontation at the North Bridge . The British troops were then engaged in a running battle on their march back to Boston , suffering heavy casualties . All of the New England colonies ( and later colonies further south ) raised militias in response to this alarm , and sent them to Boston . Siege . Digging in . Immediately after the battles of April 19 , the Massachusetts militia , under the loose leadership of William Heath , who was superseded by General Artemas Ward late on the 20th , formed a siege line extending from Chelsea , around the peninsulas of Boston and Charlestown , to Roxbury , effectively surrounding Boston on three sides . They particularly blocked the Charlestown Neck ( the only land access to Charlestown ) , and the Boston Neck ( the only land access to Boston , which was then a peninsula ) , leaving only the harbor and sea access under British control . In the days immediately following , the size of the colonial forces grew , as militias from New Hampshire , Rhode Island , and Connecticut arrived on the scene . General Gage wrote of his surprise of the number of rebels surrounding the city : " The rebels are not the despicable rabble too many have supposed them to be . . . In all their wars against the French they never showed such conduct , attention , and perseverance as they do now . " General Gage turned his attention to fortifying easily defensible positions . In the south , at Roxbury , Gage ordered lines of defenses with 10 twenty - four pound guns . In Boston proper , four hills were quickly fortified . They were to be the main defense of the city . Over time , each of these hills were strengthened . Gage also decided to abandon Charlestown , removing the beleaguered forces ( that had retreated from Concord ) to Boston . The town of Charlestown itself was entirely vacant , and the high lands of Charlestown ( Bunker Hill and Breed ' s Hill ) were left undefended , as were the heights of Dorchester , which had a commanding view of the harbor and the city . The British at first greatly restricted movement in and out of the city , fearing infiltration of weapons . Besieged and besiegers eventually reached an informal agreement allowing traffic on the Boston Neck , provided no firearms were carried . Residents of Boston turned in almost 2 , 000 muskets , and most of the Patriot residents left the city . Many Loyalist s who lived outside the city of Boston left their homes and fled into the city . Most of them felt that it was not safe to live outside of the city , because the Patriots were now in control of the countryside . Some of the men , after arriving in Boston , joined Loyalist regiments attached to the British army . Since the siege did not blockade the harbor , the city remained open for the Royal Navy under Vice Admiral Samuel Graves to sail in supplies from Nova Scotia and other places . Colonial forces could do little to stop these shipments due to the naval supremacy of the British fleet and the complete absence of any sort of rebel armed vessels . Nevertheless , the town and the British forces were on short rations , and prices rose quickly . In addition , the American forces generally had information about what was happening in the city , but General Gage had no effective intelligence of rebel activities . Early skirmishes . On May 3 , the Massachusetts Provincial Congress authorized Benedict Arnold to raise forces for taking Fort Ticonderoga near the southern end of Lake Champlain in the Province of New York , which was known to have heavy weapons , and to be only lightly defended . Arnold arrived in Castleton ( in what is now Vermont , but was then disputed territory between New York and New Hampshire ) on the 9th , where he joined with Ethan Allen and a militia company from Connecticut , all of whom had independently arrived at the idea of taking Ticonderoga . This company , under the joint leadership of Arnold and Allen , captured Fort Ticonderoga and Fort Crown Point . They also captured the one large military vessel on Lake Champlain in a raid on Fort Saint - Jean . They recovered over 180 cannons , as well as other weaponry and supplies that the nascent Continental Army would find useful in tightening their grip on Boston . In Boston , there was no regular supply of fresh meat , and many horses needed hay . On May 21 , Gage ordered a party to go to Grape Island , in the outer harbor , and bring hay to Boston . When the Continentals on the mainland noticed this , they took alarm , and the militia were called out . As the British party arrived , they came under fire from the militia . The militia set fire to a barn on the island , destroying 80 tons of hay , and prevented the British from taking more than 3 tons . Continental forces , partly in response to the Grape Island incident , worked to clear the harbor islands of livestock and supplies useful to the British . On May 27 , in the Battle of Chelsea Creek , the British Marines attempted to stop removal of livestock from some of the islands . The Americans resisted , and , in the course of the action , the British schooner " Diana " ran aground and was destroyed , but not before the Continentals recovered its weaponry . In an attempt to help quell the rebellion , Gage issued a proclamation on June 12 offering to pardon all of those who would lay down their arms , with the exception of John Hancock and Samuel Adams . Instead of quelling the rebellion , it ignited anger among the Patriots , and more people began to take up arms . Breed ' s Hill . Throughout May , the British had been receiving reinforcements , until they reached a strength of about 6 , 000 men . On May 25 , three Generals arrived on : William Howe , John Burgoyne , and Henry Clinton . Gage began planning to break out of the city . The plan decided on by the British command was to fortify both Bunker Hill and Dorchester Heights . They fixed the date for taking Dorchester Heights at June 18 . On June 15 , the colonists ' learned of the British plans . In response , they sent instructions to General Ward to fortify Bunker Hill and the heights of Charlestown ; he ordered Colonel William Prescott to do so . On the night of June 16 , Prescott led 1 , 200 men over the Charlestown Neck , and constructed fortifications on Bunker Hill and Breed ' s Hill . On June 17 , in the Battle of Bunker Hill , British forces under General Howe took the Charlestown peninsula . The British succeeded in their tactical objective of taking the high ground on the Charlestown peninsula , but they suffered significant losses . With some 1 , 000 men killed or wounded , including 92 officers killed , the British losses were so heavy that there were no further direct attacks on American forces . The Americans , while losing the battle , had again stood against the British regulars with some success , as they had successfully repelled two assaults on Breed ' s Hill during the engagement . From this point , the siege essentially became a stalemate . Stalemate . On July 3 , George Washington arrived to take charge of the new Continental Army . He set up his headquarters at a house in Cambridge that would later also become well known as the home of Henry Wadsworth Longfellow . By this time forces and supplies were arriving , including companies of riflemen from as far away as Maryland and Virginia . Washington began the work of molding the militias into something more closely resembling an army , appointing senior officers ( where the militias had typically elected their leaders ) , and introducing more organization and disciplinary measures to the encamped militias . He required officers of different ranks to wear differentiating apparel , so that they might be distinguished from their underlings and superiors . Toward the end of July , about 2 , 000 riflemen arrived in units raised in Pennsylvania , Maryland , and Virginia . The accuracy of the rifle was previously unknown in New England , and these forces were used to harass the besieged forces . Washington also ordered the defenses to be improved . Trenches were dug on the Boston Neck , and then extended toward Boston . However , these activities had little effect on the British occupation . The working parties were fired on from time to time , as were sentries guarding the works . On July 30 , in retaliation for an American attack , the British pushed back an American advanced guard , and burned a few houses in Roxbury . Four days later , on August 2 , an American rifleman was killed , and his body hung up by the neck . In retaliation , other American riflemen marched to the lines and began to attack the British troops . They continued their sharp shooting all day , killing or wounding many of the British , and losing only one man . On August 30 , the British made a surprise breakout from the Boston Neck , set fire to a tavern , and withdrew to their defenses . On the same night , 300 Americans attacked Lighthouse Island and burned the lighthouse , killing several British soldiers and capturing 23 at the loss of one life . On another August night , Washington sent 1 , 200 men to dig entrenchments on a hill near the Charlestown Neck . Despite a British bombardment , the Americans successfully dug the trenches . In early September , Washington began drawing up plans for two moves : first , to dispatch 1 , 000 men from Boston and invade Quebec , and second , to launch an attack on Boston . Washington felt that he could afford to send some troops to Quebec , as he had received intelligence from British deserters and American spies that the British had no intention of launching an attack from Boston until they were reinforced . On September 11 , about 1 , 100 troops under the command of Benedict Arnold left for Quebec . Washington summoned a council of war , and made a case for an all out amphibious assault on Boston , by sending troops across Back Bay in flat - bottomed boats which could hold 50 men each . Washington believed it would be extremely difficult to keep the men together when winter came . In a war council , the plan was unanimously rejected , and the decision was not to attack " for the present at least . " In early September Washington authorized the appropriation and outfitting of local fishing vessels for intelligence - gathering and interdiction of supplies to the British . This activity was a precursor to the Continental Navy , which was established in the aftermath of the British Burning of Falmouth ( present - day Portland , Maine ) . The provincial assemblies of Connecticut and Rhode Island had by then also begun arming ships and authorized privateer ing . In early November , 400 British soldiers went to Lechmere ' s Point on a raiding expedition to acquire some livestock . They made off with 10 head of cattle , but lost two lives in the skirmish with colonial troops sent to defend the point . On November 29 , colonial Captain John Manley , commanding the schooner " Lee " , captured one of the most valuable prizes of the siege , the British brigantine " Nancy " , just outside Boston Harbor . She was carrying a large supply of ordnance and military stores intended for the British troops in Boston . As winter approached , both sides faced their own problems . The Americans were so short on gunpowder that soldiers were given spears to fight with in the event of a British attack . Many of the American troops remained unpaid and many of their enlistments would be up at the end of the year . On the British side Howe , who had replaced Gage as commander in October , was faced with different problems . Wood was so scarce that they began cutting down trees and tearing down wooden buildings , including the Old North Meeting House . To add to this , supplying the city had become increasingly difficult because of winter storms and the rise in rebel privateers . The British troops were so hungry that many were ready to desert as soon as they could . Worse , scurvy and smallpox had broken out in the city . Washington again proposed to assault Boston in October , but his officers thought it best to wait until the harbor had frozen over . In February , when the water had frozen between Roxbury and Boston Common , Washington thought that in spite of his shortage in powder he would try an assault by rushing across the ice ; but his officers again advised against it . Washington ' s desire to launch an attack on Boston arose from his fear that his army would desert in the winter , and how easily he knew that Howe could break the lines of his army in its present condition . He had not yet learned how completely he could trust in Howe ' s inactivity ; he abandoned an attack across the ice with great reluctance in exchange for a more cautious plan , to fortify Dorchester Heights using cannon arrived from Fort Ticonderoga . In mid - January , on orders from London , British Major General Henry Clinton and a small fleet set sail for the Carolinas with 1 , 500 men . Their objective was to join forces with additional troops arriving from Europe , and to take a port in the southern colonies for further military operations . In early February a British raiding party crossed the ice and burned several farmhouses in Dorchester . End of the siege . Between November 1775 and February 1776 , Colonel Henry Knox and a team of engineers used sled ges 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 . Fortification of Dorchester Heights . 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 . Evacuation . 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 . Aftermath . Americans clean up . Once the British fleet sailed away , the Americans moved to reclaim Boston and Charlestown . At first , they thought that the British were still on Bunker Hill , but it turned out that the British had left dummies in place . Due to the risk of smallpox , at first only men picked for their prior exposure to the disease entered Boston under the command of Artemas Ward . More of the colonial army entered on March 20 , once the risk of disease was judged low . While Washington had essentially acceded to the British threat to burn Boston , and had not hindered their departure from the city , he did not make their escape from the outer harbor entirely easy . He directed Captain Manley to harass the departing British fleet , in which he had some success , capturing among other prizes the ship carrying Crean Brush and his plunder . General Howe , when his fleet finally left the outer harbor , left in his wake a small contingent of vessels whose primary purpose was to intercept any arriving British vessels . While they successfully redirected to Halifax numerous ships carrying British troops originally destined for Boston , some unsuspecting British troop ships landed in Boston , only to fall into American hands . The British departure ended major military activities in the New England colonies . Washington , fearing that the British were going to attack New York City , departed on April 4 with his army for Manhattan , beginning the New York and New Jersey campaign . There are six units of the Army National Guard ( 101st Eng Bn , 125th MP Co , 181st Inf , 182nd Inf , 197th FA , and 201st FA ) derived from American units that participated in the Siege of Boston . There are thirty currently existing units in the U . S . Army with lineages that go back to the colonial era . Fate of the British generals . General Howe would be severely criticized in the British press and Parliament for his failures in the Boston campaign . General Gage was never given another command . General Burgoyne would see action in the Saratoga Campaign , a disaster that saw his capture , as well as that of 7 , 500 troops under his command . General Clinton would command the British forces in America for four years ( 1778 – 1782 ) . Fate of the Loyalists . Many Massachusetts Loyalists left with the British when they evacuated Boston . Some went to England to rebuild lives there , and some returned to America after the war . Many stayed in Nova Scotia , settling in places like Saint John , and many became active in the future development of Nova Scotia and New Brunswick . Fate of Boston . Boston effectively ceased to be a military target . It continued to be a focal point for revolutionary activities , with its port acting as an important point for fitting ships of war and privateers . Its leading citizens would have important roles in the development of the future United States . Boston and other area communities mark the March 17 end of the siege as Evacuation Day .