On the night of June 16th, about 1,200 men of the Colonial force besieging Boston moved on to the Charlestown isthmus overlooking the city and threw up entrenchments on Breed's Hill. The British garrison reacted promptly to this threat. On the 17th, 2,200 troops under Maj. Gen. William Howe were ferried across to the isthmus and stormed the American positions on Breed's Hill. In the ensuing battle, incorrectly named after Bunker Hill which stands nearby, the British drove the Colonials from the isthmus after three assaults, but at a cost of about 1,000 in killed and wounded as compared with American losses of approximately 400 killed and wounded. Some 3,030 patriots took part in the fighting at one time or another. This proved to be the only major engagement of the prolonged siege of Boston.
Gen. George Washington took formal command of the besieging army on July 3rd and devoted the next several months to building up the American force and trying to solve its severe logistical difficulties.
At the same time, steps were taken to send an expedition against British-held Fort Ticonderoga on Lake Champlain, a strategic post well-supplied with artillery and military stores much needed by the American forces investing Boston.
Early on May 10th, a New England force of some 80 men led by Cols. Ethan Allen of Vermont and Benedict Arnold of Connecticut surprised the British garrison of about 40 men, which surrendered without a fight. Following this success, Allen seized Crown Point on the 12th and Arnold temporarily occupied St. John's, a fort across the Canadian border, on the 16th. Subsequently, a large part of the 100 cannon and substantial military stores captured at Ticonderoga were laboriously hauled overland to Boston under the direction of Maj. Gen. Henry Knox, of Washington's artillery, to supply the army besieging the city.
By March 1776, Washington had an army of 14,000 men. On March 4th, he moved suddenly to install artillery on Dorchester Heights and, a short time later, on Nook's Hill, positions that dominated Boston from the south. The British commander, Howe, now recognized the serious difficulty of his position. He evacuated the city by the 17th, and on the 26th, sailed with about 9,000 men for Halifax, N. S.