Siege of Boston (1775–1776) – Washington, Dorchester Heights & the British Evacuation

Battle at a Glance

Historical Background: From Imperial Crisis to Armed Siege

Boston Under British Occupation

Boston had been a center of colonial resistance to British imperial policy for years before the Revolutionary War. The stationing of British troops beginning in 1768, the Boston Massacre of 1770, the destruction of East India Company tea in December 1773, and Parliament’s subsequent Coercive Acts deepened the confrontation between Massachusetts and the British government.

The Massachusetts Government Act restricted traditional forms of provincial self-government, while the Boston Port Act closed the port to most commerce. General Thomas Gage, appointed royal governor of Massachusetts, commanded the British troops stationed in Boston.

Outside the town, provincial leaders organized militia companies, gathered weapons and ammunition, and developed institutions capable of resisting royal authority. By early 1775, Massachusetts possessed an increasingly organized military opposition to British rule.

Lexington and Concord: April 19, 1775

During the night of April 18–19, Gage sent British regulars toward Concord to seize or destroy military supplies. The expedition encountered armed Massachusetts militia at Lexington, where shots were fired and several colonists were killed.

At Concord, fighting developed near the North Bridge. As British troops withdrew toward Boston, militia companies from surrounding towns attacked the column along the roads through Middlesex County.

The British suffered substantial casualties during the retreat. Reinforcements under Brigadier General Hugh Percy helped the surviving troops return to the protection of Boston’s defenses.

By the following day, thousands of provincial soldiers had gathered outside Boston. What began as a British expedition to confiscate military supplies had become an armed confrontation in which the royal army was surrounded by hostile provincial forces.

The Provincial Army Encircles Boston

Massachusetts troops established positions in Cambridge, Roxbury and other communities controlling the principal land approaches to Boston. Militia from Connecticut, New Hampshire and Rhode Island soon joined them.

General Artemas Ward, a Massachusetts officer with previous military experience, emerged as the senior commander of the provincial forces.

The Americans could prevent British troops from moving freely into the countryside, but they lacked the artillery, ammunition and training necessary to assault Boston’s fortified positions.

The British retained access to the sea through the Royal Navy, allowing supplies and reinforcements to reach the garrison despite the landward encirclement.

Fort Ticonderoga and the Artillery Problem

On May 10, 1775, American forces led by Ethan Allen and Benedict Arnold captured Fort Ticonderoga on Lake Champlain.

The fort contained artillery that would later become crucial to the Siege of Boston. However, transporting heavy cannon across hundreds of miles of difficult terrain presented an enormous logistical challenge.

During the early months of the siege, the Americans possessed too few suitable heavy guns and insufficient gunpowder to conduct sustained bombardment or force the British from the town.

The Battle of Bunker Hill

In June 1775, American commanders learned that the British might occupy high ground overlooking Boston. Provincial troops moved onto the Charlestown Peninsula during the night of June 16–17 and constructed a redoubt on Breed’s Hill, along with supporting defenses.

On June 17, British forces attacked the American positions. The defenders repelled repeated advances before British troops captured the redoubt in a final assault.

The British secured the Charlestown Peninsula but suffered exceptionally heavy casualties, including many officers. The battle demonstrated that American provincial troops could resist British regulars from prepared positions, while also revealing the limitations imposed by inadequate ammunition and uneven command coordination.

The British victory did not break the siege. Instead, the opposing armies settled into an extended confrontation around Boston.

The Continental Congress Takes Command

On June 14, 1775, the Second Continental Congress adopted the forces surrounding Boston as the Continental Army. The following day, Congress appointed George Washington commander in chief.

Washington arrived at Cambridge in early July and formally assumed command on July 3.

He inherited an army with serious organizational problems. The troops came from several colonies, possessed different enlistment arrangements, and lacked standardized equipment and military administration.

Washington’s immediate challenge was to transform a large provincial encampment into a coordinated army capable of maintaining the siege.

Commanders & Participating Forces

The forces surrounding Boston changed substantially during the siege. The initial provincial army consisted primarily of New England militia and locally raised regiments. Over time, these forces were reorganized under Continental authority, while British reinforcements and command changes altered the composition of the garrison.

American Commanders

British Commanders

Massachusetts Provincial Troops

Massachusetts provided the largest proportion of the troops initially surrounding Boston. Regiments were raised under provincial authority and drew soldiers from towns throughout the colony.

These units included veterans of earlier colonial wars, local militia officers, farmers, artisans, laborers and other civilians who had mobilized after Lexington and Concord.

Connecticut Troops

Connecticut contributed substantial forces under officers including Israel Putnam and other provincial commanders. Connecticut regiments participated in the siege lines and the fighting around Charlestown.

New Hampshire Troops

New Hampshire soldiers served prominently in the northern siege positions and at Bunker Hill. Regiments associated with John Stark and James Reed became especially important during the June 17 battle.

Rhode Island Troops

Rhode Island provided troops under commanders including Nathanael Greene. These regiments participated in the siege and contributed to the emerging Continental military organization.

The British Garrison

The British army in Boston included regular infantry, grenadiers, light infantry, artillerymen and Royal Marines. The Royal Navy maintained the maritime communications necessary to supply and eventually evacuate the garrison.

British military strength varied as reinforcements arrived, casualties accumulated, and units were reorganized or assigned to new operations.

Battlefield Geography & Terrain

The geography of eighteenth-century Boston was fundamentally different from the modern city. Boston occupied a peninsula connected to the mainland by a narrow neck of land, while surrounding hills and waterways created natural defensive positions.

Why Dorchester Heights Was Decisive

Throughout the siege, the British relied upon Boston Harbor to sustain the garrison. Dorchester Heights overlooked portions of the harbor and offered elevated positions from which American artillery could threaten British shipping and the town.

Occupying the heights did not automatically destroy the British fleet, but it created an unacceptable strategic risk. Howe faced the prospect of attacking a strongly fortified position or abandoning Boston.

Weapons, Equipment & Logistics

The American Gunpowder Shortage

One of Washington’s greatest difficulties was the Continental Army’s inadequate supply of gunpowder. The army possessed muskets and some artillery, but its powder reserves were insufficient for prolonged offensive operations.

Washington therefore had to conserve ammunition while maintaining the appearance of a credible military threat. The shortage made a direct assault on Boston particularly hazardous.

American Infantry Weapons

Provincial and Continental soldiers carried a variety of smoothbore muskets and other firearms. Weapons and equipment were not standardized, and some soldiers lacked bayonets or suitable cartridge supplies.

These deficiencies complicated training and limited the army’s ability to conduct coordinated offensive operations against British regulars.

British Infantry and Artillery

British troops possessed established military organization and experience in conventional infantry tactics. Their equipment included smoothbore muskets, socket bayonets and artillery supported by trained crews.

The British also benefited from naval guns and the logistical support of the Royal Navy.

The Capture of Fort Ticonderoga

The American capture of Fort Ticonderoga in May 1775 made heavy artillery available, but the guns remained far from Boston.

Washington recognized that these cannon could help overcome the limitations of the siege, particularly if placed on commanding high ground.

Henry Knox’s Artillery Expedition

In November 1775, Henry Knox traveled to Fort Ticonderoga to organize the transportation of heavy artillery to Massachusetts.

The expedition moved approximately sixty tons of cannon and related equipment across difficult roads, waterways and winter terrain. Knox used boats, sledges, teams of oxen and local assistance to complete the journey.

The artillery arrived in the Boston area during January 1776, dramatically increasing Washington’s ability to threaten British positions.

Fortification Materials

American soldiers constructed earthworks using timber, fascines, gabions, barrels filled with earth and other materials. Engineers sought to create positions capable of protecting infantry and artillery from British fire.

These methods were especially important during the rapid occupation of Dorchester Heights, where the Americans needed to establish substantial defenses before the British could respond.

British Supply Difficulties

Although the British retained access to the sea, the garrison faced problems obtaining adequate food, fuel and other necessities. The surrounding countryside was controlled by hostile American forces, and supplies had to be imported or acquired through limited local operations.

Winter conditions, disease and the presence of civilians added to the difficulties of maintaining the army inside Boston.

Intelligence & Operational Planning

British Plans to Break the Encirclement

During the early siege, British commanders considered operations against the American positions surrounding Boston. The Battle of Bunker Hill demonstrated that British regulars could capture prepared American works, but the cost was severe.

The heavy casualties of June 17 encouraged greater caution in subsequent planning.

Washington’s Strategic Problem

Washington wanted to remove the British from Boston without sacrificing the Continental Army in an assault against fortified positions.

His army lacked sufficient ammunition and heavy artillery for much of 1775. The British also retained naval superiority, complicating any attempt to isolate the town completely.

Washington consequently maintained the siege while strengthening his army, improving its organization and seeking opportunities to threaten the British position indirectly.

Intelligence and Observation

Both armies relied upon scouts, local inhabitants, deserters, intercepted correspondence and observations from elevated positions to understand enemy movements.

American commanders monitored British fortifications and naval activity, while the British sought information about American strength, supplies and intentions.

Because neither army possessed complete information, commanders frequently had to make decisions based upon incomplete or contradictory reports.

The Dorchester Heights Plan

By early 1776, Knox’s artillery had provided Washington with the means to threaten Boston from elevated positions.

Washington and his officers developed a plan to occupy Dorchester Heights rapidly, establish strong defensive works and position artillery capable of threatening British ships and installations.

The operation required careful preparation. Materials were assembled in advance so that soldiers could construct defenses during a single night.

The March 2–4 Bombardments

American batteries opened bombardments against British positions during the nights preceding the occupation of Dorchester Heights. The cannon fire helped divert British attention and supported the larger operation.

The bombardments also demonstrated the increasing capability of the American artillery.

The Night of March 4–5

Under the direction of General John Thomas, American troops moved onto Dorchester Heights and constructed substantial earthworks under cover of darkness.

By morning, British observers discovered that the Americans had established fortified positions on commanding ground.

The speed of the operation surprised the British and fundamentally altered the military situation.

Howe’s Decision

Howe initially considered an assault to remove the Americans from Dorchester Heights. British troops prepared for an operation, but severe weather disrupted the plan.

With the American fortifications strengthening and the harbor increasingly vulnerable, Howe determined that evacuation offered the safer course.

The Siege Unfolds: Interactive Timeline

Expand the entries below to follow the siege from the fighting at Lexington and Concord through the British evacuation of March 17, 1776. The timeline distinguishes major engagements from the continuing operations of the encirclement.

Tactical Analysis & Command Decisions

The American Encirclement

The siege began as a rapid mobilization of provincial militia following the British retreat from Concord. The Americans occupied positions controlling the principal land approaches to Boston.

This arrangement prevented the British army from operating freely in the surrounding countryside, but it did not completely isolate the garrison because the Royal Navy maintained access to the harbor.

The British Position at Boston Neck

Boston Neck was the principal land connection between Boston and the mainland. British fortifications and artillery made a direct American assault along this narrow approach especially dangerous.

The Americans therefore relied upon containment, fortified positions and the gradual improvement of their military capabilities rather than an immediate attempt to storm the town.

The Battle of Bunker Hill

The British attack on June 17 demonstrated both the strength and limitations of eighteenth-century infantry assaults against prepared defenses.

American troops inflicted severe losses upon advancing British formations, but ammunition shortages and the eventual collapse of the defensive position allowed the British to capture the Charlestown heights.

The battle reinforced the importance of earthworks and elevated artillery positions while discouraging further costly frontal attacks.

The Strategic Deadlock

For much of 1775, neither army could easily force a decisive result. The British lacked freedom of movement on land, while the Americans lacked the heavy artillery and ammunition necessary to compel the garrison to surrender.

The arrival of Knox’s artillery changed the military balance by providing the Americans with weapons capable of threatening British positions from elevated ground.

The Dorchester Heights Operation

The fortification of Dorchester Heights was a carefully planned engineering and logistical operation. American commanders prepared materials in advance, moved troops onto the heights under cover of darkness and rapidly constructed defenses capable of supporting artillery.

The success of the operation depended upon secrecy, coordinated labor, engineering knowledge and the ability to complete the works before the British could intervene.

Why Howe Chose Evacuation

Howe’s army could not remain safely in Boston if American artillery controlled positions capable of threatening the harbor and British shipping.

An assault against Dorchester Heights might have removed the threat, but the Americans had constructed strong defenses and the British had already experienced the cost of attacking fortified heights at Bunker Hill.

After weather disrupted the planned assault, evacuation became the more practical military decision.

Why the Siege Ended Without a Final Battle

The decisive operation was not a major infantry assault but the occupation of commanding terrain. Washington used artillery, engineering and geography to make the British position strategically untenable.

The British departure therefore represented a successful American siege operation even though the final days did not produce a large battlefield engagement.

The Soldier’s Experience

The First Provincial Encampments

Many soldiers who surrounded Boston in April 1775 had left farms, workshops and households with little preparation for prolonged military service. They arrived in militia companies organized around their home communities and local officers.

The transition from temporary mobilization to a sustained siege required men to build shelters, establish camps, perform guard duty and adapt to military discipline.

Life in the Siege Lines

Most soldiers did not spend every day in combat. Their duties included constructing fortifications, standing guard, gathering firewood, maintaining weapons, moving supplies and observing British positions.

Exposure to rain, cold, poor sanitation and crowded quarters contributed to illness. Maintaining adequate food, clothing and shelter became a constant concern for officers and enlisted men alike.

The Soldiers at Bunker Hill

For the provincial troops on Breed’s Hill, June 17 brought intense artillery fire and repeated British infantry assaults. Defenders fought from earthworks and improvised positions, often at relatively close range.

The shortage of ammunition became increasingly serious as the battle continued. Many Americans eventually withdrew as British troops entered the redoubt and surrounding defenses.

The experience demonstrated both the effectiveness of prepared positions and the extreme danger faced by soldiers defending them.

British Soldiers Inside Boston

British regulars lived within a confined military occupation surrounded by hostile forces. The garrison depended upon maritime supply lines and faced shortages of food, fuel and other necessities.

Soldiers also endured disease, difficult living conditions and the uncertainty of a campaign that offered few opportunities for decisive action after Bunker Hill.

Boston’s Civilian Population

Civilians remaining in Boston experienced shortages, restrictions on movement and the consequences of prolonged military occupation.

Some inhabitants supported the Crown, while others opposed British authority. Political loyalties, family circumstances and economic necessity shaped individual experiences.

As the siege continued, the town’s commercial activity remained severely disrupted.

The Artillery Expedition

Men assisting Henry Knox faced an entirely different form of military hardship. Moving heavy cannon through winter conditions required physical labor, transportation skills and cooperation with local communities.

Frozen waterways, difficult roads and the enormous weight of the guns made the expedition dangerous even without enemy fire.

The Night on Dorchester Heights

American soldiers assigned to fortify Dorchester Heights worked under the pressure of completing substantial defenses before daylight.

They moved earth, positioned prepared materials, constructed protective works and prepared artillery positions while attempting to avoid detection.

The labor was essential to the operation’s success. By morning, the newly constructed defenses presented the British with a military problem they could not easily resolve.

Evacuation Day

On March 17, 1776, British troops boarded transports and departed Boston. Loyalist civilians also left with the army, abandoning homes and property amid uncertainty about their future.

For American soldiers, entering Boston marked the successful conclusion of months of service. Yet the war was far from over, and many units soon prepared for further operations elsewhere.

Where Was Your Ancestor’s Unit?

The Siege of Boston is particularly important for descendants of soldiers who served in Massachusetts, Connecticut, New Hampshire and Rhode Island provincial regiments during 1775 and the Continental Army during early 1776.

Because the siege lasted nearly eleven months, researchers must establish precisely when a soldier served, under which commander and at which position.

Units and Research Questions

Provincial Service Versus Continental Service

Many soldiers enlisted under provincial arrangements in 1775 and later entered reorganized Continental units. A soldier’s regiment or commanding officer may therefore change in the records even when he continued serving in the Boston area.

Researchers should not assume that a unit bearing a familiar commander’s name remained unchanged throughout the siege.

Researching Bunker Hill Participation

A soldier’s presence in the Siege of Boston does not establish participation at Bunker Hill. The June 17 battle involved specific units and detachments on the Charlestown Peninsula.

Contemporary returns, pension testimony and reliable regimental studies are necessary to determine whether an individual soldier was present during the engagement.

Researching Dorchester Heights Participation

The March 4–5 operation involved troops assigned to the fortification effort, supporting batteries and nearby defensive positions.

Membership in the Continental Army during March 1776 does not automatically establish that a soldier worked on Dorchester Heights.

Researchers should seek orders, unit assignments, journals and pension declarations that connect the soldier or his unit to the operation.

Understanding Pension Declarations

Later pension applications may describe service at Cambridge, Roxbury, Prospect Hill, Winter Hill or Boston. These references should be compared with enlistment dates, commanding officers and contemporary military returns.

Statements such as “served at the siege of Boston” may establish general campaign participation but do not necessarily identify a particular battlefield action.

Battle Outcome & Casualties

The British Evacuate Boston

On March 17, 1776, British troops evacuated Boston after Washington’s army occupied Dorchester Heights and threatened the harbor with artillery.

The Americans entered the town without having to conduct a final major assault against the British fortifications.

Casualties During the Siege

The siege included several engagements, most notably Lexington and Concord and the Battle of Bunker Hill. Casualty totals vary depending upon whether historians count only combat losses, include smaller skirmishes or attempt to estimate deaths from disease.

The Battle of Bunker Hill alone produced approximately 1,054 British casualties and approximately 450 American casualties, according to commonly cited returns.

These figures should not be added together and presented as a definitive siege-wide total without specifying the events and categories included.

Military Equipment and Property

British troops removed substantial military equipment during the evacuation, but some guns, supplies and other materials were abandoned or rendered unusable.

The evacuation also involved the departure of Loyalist civilians who feared remaining under American control.

Who Won the Siege?

The Americans achieved a strategic victory. They compelled the British army to abandon Boston, ending the occupation and securing Massachusetts from the immediate threat posed by the garrison.

The victory did not destroy the British army, which withdrew by sea and remained available for future campaigns.

Why the Result Mattered

The siege demonstrated that the Continental Army could maintain a prolonged military operation and use artillery, fortifications and favorable geography to compel a stronger professional army to withdraw.

It also provided Washington with an important early success as commander in chief.

Strategic Significance & Aftermath

The End of British Control in Boston

The evacuation of March 17 ended the British military occupation of Boston and the first major campaign of the Revolutionary War.

The departure secured the town for the American cause and removed the immediate British military presence from Massachusetts.

Washington’s First Major Strategic Success

Washington had inherited an army with serious shortages of ammunition, artillery and administrative organization. Over the following months, he maintained the siege while improving the Continental Army’s effectiveness.

The occupation of Dorchester Heights demonstrated his ability to coordinate engineering, artillery and infantry operations toward a decisive strategic objective.

The Importance of Henry Knox

Knox’s artillery expedition provided the heavy guns necessary to threaten Boston from elevated positions. Without the artillery transported from Fort Ticonderoga, the Dorchester Heights operation would have been far less effective.

The expedition became an enduring example of the importance of logistics in military history.

British Forces Regroup at Halifax

Howe’s army sailed to Halifax, Nova Scotia, where it regrouped before further operations. The British government had not abandoned its effort to suppress the rebellion.

The evacuation represented a setback, not the end of British military power in North America.

The Campaign Shifts to New York

Washington recognized that New York would likely become the next major British objective. The city possessed a valuable harbor and important connections to the Hudson River.

After the evacuation of Boston, Continental troops began moving south to strengthen New York’s defenses.

The subsequent campaign would culminate in the Battle of Long Island and the loss of New York City.

The Meaning of Evacuation Day

March 17 became known in Massachusetts as Evacuation Day, commemorating the British departure from Boston.

The anniversary reflects the importance of the siege in the history of Massachusetts and the early Revolutionary War.

The Siege’s Place in the Revolutionary War

The Siege of Boston established several themes that would recur throughout the war: the importance of preserving the Continental Army, the value of fortified positions, the difficulties of supply and ammunition, and the strategic influence of geography.

It also showed that American forces could achieve important military objectives without defeating British regulars in a large open-field battle.

Primary Sources & Historical Research

The Siege of Boston is documented through military correspondence, orders, journals, contemporary maps, artillery records, provincial returns and British naval reports. These sources allow historians to reconstruct both the military operations and the difficulties of maintaining the opposing armies.

Primary Sources and Archival Leads

1. George Washington’s correspondence, 1775–1776. Letters and reports concerning army organization, ammunition shortages, fortifications and the operations leading to the British evacuation.
2. General Orders of the Continental Army. Documents concerning discipline, troop assignments, defensive preparations and siege operations.
3. Artemas Ward’s military papers. Important sources for the initial provincial encirclement and American command arrangements.
4. Henry Knox’s correspondence and artillery records. Evidence concerning the transportation of cannon from Fort Ticonderoga and the development of American artillery capabilities.
5. British military correspondence of Thomas Gage and William Howe. Documents concerning the garrison, Bunker Hill, the siege and evacuation.
6. Royal Navy reports and correspondence. Sources concerning the supply of Boston, harbor operations and the evacuation fleet.
7. Contemporary maps of Boston and surrounding communities. Essential for reconstructing the original coastline, fortified positions and approaches to the town.
8. Provincial and Continental muster rolls. Evidence for the organization, strength and service of American regiments during the siege.

Historical Research and Battlefield Interpretation

1. George Washington’s Mount Vernon — Siege of Boston. Historical encyclopedia article.
2. National Park Service — Boston National Historical Park. Historical sites and interpretation.
3. National Park Service — Dorchester Heights. Dorchester Heights history.
4. American Battlefield Trust — Siege of Boston. Campaign overview.
5. American Battlefield Trust — Bunker Hill. Battle overview and casualty information.
6. Founders Online — National Archives. Washington’s correspondence and documentary editions.
7. Library of Congress — Maps and Collections. Contemporary maps and historical documents.
8. National Archives — Revolutionary War Records. Military records and genealogical research.
9. Massachusetts Historical Society. Manuscript collections and historical research.
10. National Park Service — American Revolution. Revolutionary War resources.

Research Limitations

The composition and strength of the American army changed repeatedly during the siege. Provincial regiments were reorganized, enlistments expired, and new Continental units entered service.

Published accounts also differ concerning troop strengths, artillery inventories, the precise number of soldiers involved in the Dorchester Heights operation and the full extent of siege-related casualties.

Researchers should distinguish contemporary military returns from later historical estimates and should avoid assigning individual soldiers to specific operations without documentary support.