The Siege of Boston
Following the opening battles of Lexington and Concord in April 1775, Colonial militia forces surrounded British-occupied Boston. When General George Washington arrived in Cambridge in July 1775 to take command of the newly formed Continental Army, he faced a difficult military situation. British forces held fortified positions inside the city, protected by Royal Navy warships anchored in the harbor.
The siege dragged through the winter of 1775-1776, with the Continental Army lacking the heavy artillery required to dislodge British troops. Washington needed a decisive strategic move to break the stalemate and liberate the city.
Henry Knox and the Noble Train of Artillery
The turning point came through the efforts of Colonel Henry Knox, a 25-year-old Boston bookseller of Irish descent. Knox proposed a daring expedition to transport heavy artillery captured from Fort Ticonderoga in upstate New York all the way to the siege lines outside Boston.
Over three grueling winter months, Knox led a detachment that hauled 59 cannons and mortars weighing a total of 60 tons across frozen rivers, snow-covered mountains, and rugged terrain. This incredible logistical effort, known as the “Noble Train of Artillery,” arrived at Washington’s camp in early 1776, providing the commander in chief with the firepower needed to challenge British control.
Fortifying Dorchester Heights
On the night of March 4, 1776, Continental troops executed a secret military operation under cover of darkness and heavy bombardment. Soldiers marched onto Dorchester Heights, a high ground commanding strategic views of both Boston and its harbor. Working through the night, they constructed prefabricated fortifications and mounted Knox’s heavy cannons atop the hills.
When British Commander General William Howe awoke on the morning of March 5th, he looked up at the Heights and reportedly remarked that the Americans had done more work in one night than his whole army could have done in months. The strategic placement of artillery rendered the British fleet in the harbor vulnerable to destruction.
March 17, 1776: The Evacuation
Recognizing that his position was untenable, General Howe ordered the complete evacuation of British land forces and Royal Navy ships. On March 17, 1776, over 11,000 British soldiers, along with hundreds of loyalist residents, boarded more than 120 ships and sailed away from Boston Harbor toward Halifax, Nova Scotia.
The departure marked the end of an eight-year British military occupation of Boston. Washington’s successful campaign secured his first victory as commander and liberated the city without a costly, bloody assault on its downtown streets.
The Origin of the Military Password
To maintain operational security and prevent Loyalist infiltration during the critical days surrounding the evacuation, Washington established daily passwords and countersigns for his troops guarding American positions.
For March 17, 1776, Washington selected “Boston” as the primary password and “Saint Patrick” as the countersign. This deliberate choice honored both the city being liberated and the heritage of the many Irish-American soldiers serving within the ranks of the Continental Army. Today, the dual observance of St. Patrick’s Day and Evacuation Day in Suffolk County preserves the memory of that strategic triumph.