After the American colonists had chased the British soldiers from Concord back to Boston on 19 April 1775, the militia formed a line across the narrow neck of land that connected the peninsula that was the city of Boston to the surrounding countryside. The British were stuck in the town and could only be relieved by sea or by breaking through the American lines. A short glance at a map shows two other peninsulas surrounding Boston in the harbor. To the south lies Dorchester Heights. The neck of land leading to this area was many times wider than that leading into Boston, but the Heights had a commanding view of the city. To the north of Boston is the Charlestown Peninsula. Besides the small settlement of Charlestown, directly across the harbor from Boston, there are a series of hills, the highest being Bunker Hill. To get to this peninsula by land, a width of ground about the size of that leading to Boston had to be crossed.
map from sonofthesouth.net
The Americans were ordered by General Artemas Ward to occupy Bunker Hill on the night of 16-17 June 1775 after receiving intelligence that the British would attempt to do so the following evening. After a meeting between some of the American commanders, it was decided to fortify Breed’s Hill first, and Bunker Hill if time permitted. The reasoning behind the decision lay in the fact that Breed’s Hill lay closer to Boston and could prevent a buffer if the British launched an attack from across the harbor.
In the morning, Charlestown was fired upon by British ships in the harbor. The Americans by this time had been working all night; they were short on all supplies – food, water and ammunition included. They were also short on sleep, and they were aware that an attack by the British must be short in coming. By afternoon no less than four British ships, bearing about forty guns, were firing from the harbor onto American positions. Colonel William Prescott, commanding the American forces, watched Sir William Howe maneuver his forces into position, and reacted by moving his men into a better defensive position. From his post on the hill, Prescott could observe almost every move made by the redcoats and make an appropriate response.
Howe lined up his men ready to attack with the bayonet in three charges. Two errors were made in the process. The British artillery was supplied with the wrong caliber balls, making them of little service and Howe was unaware of the some of the American positions. Most importantly, Howe did not know of Stark’s men on the beach where the British would make their initial charge.  The resulting British offensive was disastrous. American fire cut down the British and stopped their advance each time, resulting in the British leaving 96 dead on the field. 
map from sonofthesouth.net
The following British advancing lines had difficulty on the approach to the American position at the rail fence because of the terrain and other obstructions. While the British fire mostly went over the heads of the Americans, the colonists fired at wave after wave of the redcoats with deadly results. After a number of charges and many men left lying on the field, the British retreated to regroup for another attack.
The next British attack was directed at the American force on Breed’s Hill. Again, the British, firing from seventy to eighty yards away, shot over the American positions. The Americans, waiting until the redcoats got closer, hit their marks, forcing another British retreat. This time, however, Howe had a more orderly retreat and was able to reform his men for a new attack. The second attack was also beaten back. Howe, now with General Henry Clinton and Robert Pigot, prepared for a three-pronged attack on Breed’s Hill, with a holding fire on Stark’s men at the rail fence. This time, with British fire seemingly surrounding the Americans, including artillery firing grapeshot, the Americans were forced to retreat as the British stormed the redoubt. The Americans had their greatest losses during the retreat.  The American forces stormed past the neck of Charlestown peninsula in their retreat, where they would build entrenchments overnight, but the British had command of both Breed’s and Bunker Hill.
Either side could lay claim to victory in the Battle of Bunker Hill. The Americans inflicted more casualties, but the British won the ground.* General Clinton summed up the battle: “A dear bought victory, another such would have ruined us.”  The battle would have an effect on the fighting in the New York-New Jersey campaign of 1776. Howe moved cautiously, with Bunker Hill always in mind, and General Nathaniel Greene was convinced that the Americans could hold Fort Washington indefinitely against a British attack using the defense at Bunker Hill as his reasoning.
* Casualty counts, as in most battles of the war, are hard to nail down. It is generally agreed that although the Americans had about 3,000 men on Charlestown peninsula, only about 1,400-1,500 were ever engaged in battle. Most accounts have the number of American casualties between 440-450 killed, wounded and captured. Similar discrepancies exist among British numbers. A number of historians agree on the British force numbering about 2,500 men, although at least one has them with over 3,000 men fighting. British casualties were about 1,150. Besides Wood, Carrington’s Battles of the American Revolution and Savas and Dameron’s A Guide to the Battles of the American Revolution were consulted for obtaining these casualty numbers.
 Wood, W.J. Battles of the Revolutionary War, 1775-1781. Chapel Hill: Da Capo Press, 2003, p. 19-20.
 Ibid, p. 22. Ibid, p. 31
 Moran, Donald N. "The Battle of Bunker Hill." Revolutionary War Archives. March 1985. http://www.revolutionarywararchives.org/battles-link/49-the-battle-of-bunker-hill (accessed January 16, 2011).