Neither the Battle of Bunker Hill nor the siege that preceded and followed it will make much sense if you don’t understand the geography of Boston as it was in the 1770s. In those years, prior to decades of land-filling, Boston was little more than an island, with only the narrowest connection overland, an ideal place for a naval power to defend.
In June, 1775, Washington had not yet arrived. The Continental Army did not yet exist. It was only two months after Lexington and Concord. The colonial militia – 15,000 strong — surrounded the town and cut off the Roxbury Neck to the south, the only land access. But of course the British navy dominated the waters of the harbor, which meant that British troops in the city could be resupplied and reinforced indefinitely. In the absence of a navy, the only way to force the British out of Boston would be to mount artillery somewhere capable of bombarding the city.
We think of Bunker Hill as being in Boston, but actually it was across the Charles River, and the battle was fought less on Bunker Hill (which commands the Charlestown Neck, the only way off the peninsula) than on Breed’s Hill, farther east. Why the British didn’t land west of Breed’s Hill, flanking it and rendering it irrelevant, says a lot about the causes and progress of the revolution. The British got a shock that day they never forgot.
The only reason the colonials were able to occupy and fortify Bunker and Breed’s Hill in the first place is that commanding officer General Thomas Gage had withdrawn the British troops to Boston after their long retreat from Concord in April. Yet if he had left a garrison on the Charlestown Peninsula, they would have had to defend against the pursuing colonial militia, so perhaps we would have seen a Bunker Hill in reverse. Hard to imagine the colonials attacking a fortified British position, though. At any rate, that isn’t what happened.
Throughout May, Gage received reinforcements, and by June he had about 6,000 men. On May 25, three generals arrived on the same ship. We know them all: William Howe (Lord When?), Gentleman Johnny Burgoyne, and Henry Clinton. If a camel is a horse designed by a committee, the assault on Breed’s Hill was strategy designed by a committee of four able generals. Gage’s plan was to take Dorchester Neck, fortifying the heights, then march on Roxbury, then take the Charlestown heights and scatter the forces in Cambridge. General Clinton wanted to attack from the Charlestown Neck, sensibly enough, but he was outvoted. Howe thought that the hill would be easy to take, and Burgoyne agreed, thinking that the “untrained rabble” would be no match for trained troops.
By the 13th the colonials knew all about the British plans. By the 15th, the Massachusetts Committee of Safety ordered defenses set up on the Charlestown Peninsula, specifically on Bunker Hill. (Bunker, not Breed’s.) On the night of the 16th, Colonel William Prescott led 1,200 men to the peninsula. They started to fortify Bunker Hill, decided that Breed’s hill was a better choice, and built their main fortification there, six-foot-high earthen walls with ditches outside them. In the morning, Prescott had breastworks built from the hill to the water on the east side, to protect from being flanked.
No point in discussing the battle in any detail. Suffice it to say that the British made three frontal assaults before they took Breed’s Hill when the colonials ran out of ammunition. In those attacks, they took terrific casualties. Of 3,000 men engaged, they lost 226 killed (including a lieutenant colonel, two majors, seven captains and nine lieutenants) and 828 wounded. In all, a third of the force went down. With respect to casualties, this was the worst single day of the war for the British; they never again lost so many men in one encounter.
American casualties came to 450, which included 115 killed. The death chiefly noted was that of Dr. Joseph Warren, the President of Massachusetts’ Provincial Congress. He had been appointed a Major General three days earlier, but since his commission had not yet taken effect he was serving as a volunteer private. Warren was killed during the retreat from Breed’s Hill on the third British charge.
It is hard to adequately estimate the effect of Bunker Hill, on either side (not to mention the large population uncommitted to either side). A faint analogy would be if a party of home-grown self-styled patriots took on a unit of the United States Army and inflicted heavy damage on it, with the obvious sympathy of a good part of the people. Regardless who held the field at the end of the day, such a battle would change everything.
The colonials abandoned the field, but they merely retreated to Cambridge and regrouped. Gage was dismissed from command as soon as London received his report, and Howe was named to succeed him. Like Clinton and Burgoyne, Howe was influenced by the slaughter he had witnessed. Perhaps this contributed to the indecisive and unaggressive style that he subsequently displayed.
As we know, within a year, cannon from Fort Ticonderoga would be installed on Dorchester Heights (at the bottom right of the map below), and the British would have to leave. The British never assaulted Dorchester Heights: After Bunker Hill, no British officer ever again had an appetite for attacking Americans in entrenched positions.