The siege was broken in March 1776 when Continental Army Colonel Henry Knox brought heavy artillery from Fort Ticonderoga to Boston during the winter, and General Washington used them to fortify Dorchester Heights, overlooking Boston and its harbour. Howe at first planned an assault on this position, but a snowstorm interfered, and he eventually decided to withdraw from Boston. On 17 March, British troops and Loyalists evacuated the city, and sailed for Halifax, Nova Scotia.