The shots fired at Lexington and Concord in April 1775 ignited the American Revolution, but it was the brutal Battle of Bunker Hill two months later that transformed a series of local skirmishes into a full-scale military campaign. This pivotal clash laid the groundwork for the birth of the American Army and an 11-month Siege of Boston.
In our special documentary, American Revolution: This is War! Bunker Hill and the Birth of the US Army, History Hit marks the 250th anniversary of the Siege of Boston (1775-1776), the foundational chapter in the eight-year fight for American Independence.
Join Dan Snow as he investigates the war’s first pitched battle – Bunker Hill – a bloody day that proved a hollow and costly British victory. Dan speaks to experts and explores this critical turning point, when skirmishes fought by colonial militia evolved into a fully-formed military campaign, as colonial forces laid siege on Boston for 11 months while the British Army tried desperately to maintain control of the town and its vital harbour.
Watch NowFollowing the initial clashes at Lexington and Concord, British forces under General Thomas Gage found themselves effectively trapped in Boston. Thousands of unorganised yet determined colonial militiamen from across New England converged around the city, loosely containing the British. Boston, a vital port and a symbolic hotbed of revolutionary sentiment, became the focal point. The British desperately sought to maintain control of the town and its crucial harbor.
Bunker Hill
Recognising the strategic importance of the hills surrounding Boston, colonial leaders decided to fortify Breed’s Hill (mistakenly named “Bunker Hill” in historical accounts) on the Charlestown Peninsula. On the night of 16 June 1775, 1,000 militiamen, led by Colonel William Prescott, hastily constructed earthen fortifications. The next day, some 2,200 British regulars, under Major General William Howe, launched a frontal assault.
The battle itself was a bloody affair. Colonial defenders held their ground against two British charges, inflicting devastating casualties. The Redcoats, advancing in disciplined ranks, were met with lethal volleys. Only on the third assault, as the Americans critically ran out of ammunition, did the British finally overrun the fortifications.
Though a tactical victory for the British, who secured the hill, it was a Pyrrhic victory of immense proportions. Over 1,000 British soldiers were killed (226) or wounded (828) – nearly half their engaged force. As Dan says, “It was the highest casualty count they suffered in a single encounter in the entire Revolutionary War”. This was compared to approximately 450 colonial casualties, of whom 140 killed mostly during the final stand and retreat.
This staggering cost sent shockwaves through the British command, shattering any illusions of a swift and easy suppression of the rebellion. In fact, they were trapped.
The Battle of Bunker Hill
Image Credit: Public Domain
The birth of an army and the long siege
Bunker Hill proved a profound turning point. For the inexperienced colonial forces, it was a massive morale boost. They had stood toe-to-toe with the world’s most formidable army and inflicted crippling losses, demonstrating that patriotic dedication, even from untrained militia, could indeed challenge superior military might. News of the battle galvanised support across the 13 colonies, uniting them in a shared sense of purpose.
Crucially, Bunker Hill underscored the urgent need for a more organised and disciplined fighting force. Just days after the battle, the Second Continental Congress, meeting in Philadelphia, took a decisive step, formally establishing the Continental Army and, on 15 June 1775, appointed a Virginian, George Washington, as its Commander-in-Chief. Washington arrived in Cambridge in early July, facing the daunting task of transforming a collection of disparate militias into a cohesive fighting machine.
As military historian Jonathan Bratten explains to Dan, “Washington’s greatest genius through the entire war and at Bunker Hill was in keeping the army together, and in keeping an army in the field.”
The Siege of Boston, which had begun informally, now intensified under Washington’s command. For the next 11 months, the Continental Army tightened its grip around the city. The British, confined to the peninsula, relied entirely on sea lines for supplies and reinforcements, making them vulnerable. Washington’s primary challenge was acquiring sufficient artillery to dislodge the entrenched British.
Gilbert Stuart Williamstown Portrait of George Washington
Image Credit: Picryl / Public Domain
The evacuation of Boston
The stalemate finally broke in early 1776, when, in a remarkable feat of logistics, Colonel Henry Knox successfully transported 59 cannons and other military supplies, captured from Fort Ticonderoga, over 300 miles of frozen terrain to Boston. On the night of 4 March Washington’s troops, under cover of darkness, fortified Dorchester Heights, overlooking Boston Harbor. By dawn, the British awoke to find American cannons aimed directly at their positions and ships.
Recognising the untenable situation, and faced with the prospect of another costly assault, or the destruction of his fleet, General Howe ordered the withdrawal. On 17 March 1776 – a day now celebrated as Evacuation Day – over 11,000 British soldiers and hundreds of Loyalists boarded ships and sailed for Halifax, Nova Scotia.
The Siege of Boston, culminating in this strategic American victory, marked a profound shift. Bunker Hill had shown the colonists could fight; the subsequent siege demonstrated they could sustain a military campaign and achieve strategic objectives. The transformation from scattered militia skirmishes to a unified, professional army had begun, setting the stage for a prolonged war for independence.
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