As the sun rose on the morning of 17 June 1775, revealing clear skies and promising warm but not unduly hot weather, several British warships in the harbor opened a bombardment of Colonel Prescott and his troops on Breed’s Hill. Many of the soldiers, exhausted from working all night and not having slept in around thirty hours, withdrew to the relative safety of Bunkers Hill. Prescott and around 200 of his Massachusetts soldiers remained in the redoubt and perhaps another 200 or so soldiers continued to man the earthwork wall that branched north from the fort toward the Mystic River.
"“ . . . On the 16th June, in the evening, I received orders to march to Breed’s Hill in Charlestown, with a party of about one thousand men, consisting of three hundred of my own regiment, Colonel Bridge and Lieut. Brickett, with a detachment of theirs, and two hundred Connecticut forces, commanded by Captain Knowlton. We arrived at the spot, the lines were drawn by the engineer, and we began the intrenchment about twelve o’clock; and plying the work with all possible expedition till just before sunrising, when the enemy began a very heavy cannonading and bombardment . . . About this time, the above field officers, being indisposed, could render me but little service, and most of the men under their command deserted the party.”"
Col. William Prescott to John Adams, 25 Aug 1775