We resume following the memoir of Surgeon’s Mate James Thacher, who became a prominent resident of Plymouth after the war. 250 years ago today, he observed great moments in the culmination of the Siege of Boston. We have already reviewed his observations of the occupation of Dorchester Heights. After that movement, the situation in Boston rapidly shifted. From those commanding hills, American artillery could now threaten the British fleet in Boston Harbor. The Royal Navy could no longer remain safely in the harbor, and the British army itself would be trapped in the town.
General William Howe understood the danger immediately. For nearly a year, his forces had held Boston while the Continental Army surrounded the city. Now the balance had suddenly turned. The Americans held the heights. The harbor was vulnerable. The position of the British army had become untenable.
Writing on March 7, 1776, Thacher noted the first clear signs that the British commander had decided the struggle for Boston was over:
There are strong indications in Boston, that the king’s troops are preparing to evacuate the town ; and that no attempt will be made to dispossess our people of the works, which we have constructed on Dorchester heights.
The long expected British assault never came. Instead, preparations began within Boston for a withdrawal. And on March 8, 1776, 250 years ago today, the momentous news reached the American camp. Thacher recorded the arrival of a flag of truce from Boston bearing a remarkable message from the town’s Aelectmen:
A flag of truce has come out of Boston with a message from the selectmen; acquainting General Washington that General Howe has come to the determination to evacuate the town ; and that he would leave it standing, provided his army should be permitted to retire without being molested. At the same time intimating, as is reported, that in case he should be attacked by our army, the town should be set on fire in different places, in order to secure his retreat. We are unacquainted with the determination of his Excellency respecting this proposition; but it is well known that he has been in favor of making an attack on the town; and that the necessary preparations were made, and the plan arranged, to be put in execution, in the event of the enemy’s meditated attack on our works at Dorchester heights. Four thousand troops, the first division commanded by General Sullivan, the second by General Greene, were ordered to be in readiness, in case the enemy had advanced and been defeated on the heights of Dorchester, this force, at a given signal, was to have rushed into the town and taken possession. It is credibly reported from Boston, that on the morning when the British officers discovered our newly erected works, which, on account of a fog loomed to great advantage, and appeared larger than the reality, General Howe, on viewing them, was heard to say in astonishment, ‘‘I know not what I shall do, the rebels have done more in one night than my whole army would have done in weeks. His admiral soon assured him that if the rebels were permitted to hold possession, he should not be able to keep a single ship in the harbor in safety.”
Howe was prepared to abandon Boston. But he warned that if his retreat were attacked, the city might be burned. Washington, for his part, had already prepared plans to storm the town if the British attempted to retake Dorchester Heights. Thousands of Continental troops stood ready to cross into Boston if the opportunity arose. The attack almost certainly would have resulted in massive American casualties and likely great calamity in assaulting such a heavily fortified town.
But the reality was becoming clear to both sides. With the Americans holding Dorchester Heights and artillery already mounted there, the British army could not remain in Boston.
General Howe had conceded the city.
Over the next several days, both armies would watch closely as preparations for the British departure quietly accelerated. The long Siege of Boston, at last, was over.
Historical Digression 