Having been dissuaded by a Council of War from ordering an all-out assault on Boston across the ice in late February 1776, Gen. George Washington moved on to Plan B: mounting heavy artillery on Dorchester Heights. On the 26th, he sent this message to the Massachusetts Council, then exercising executive power in the province:
As I am making all possible preparation to take possession of the Heights of Dorchester (which I expect I shall be able to accomplish by the latter end of this Week). It is expected that this, if any thing can, will bring the Enemy out of Boston to oppose, as at Charlestown [i.e., the Battle of Bunker Hill], our Erecting any Works there.—The photo above shows Gen. Thomas’s headquarters in Roxbury. At the beginning of the war, Thomas and the other top officers in the southern half of the siege lines tended to act somewhat independently of Cambridge headquarters. They sat down to discuss all the orders that came from north of the Charles River. One of Washington’s challenges soon after he arrived was to establish stronger connections with the officers and men in that portion of the army. Now they would be the main support of the Continental artillery’s attack on the British.
To weaken our Lines on the North side of Cambridge River, to strengthen those of Dorchester, before any movement is made that way by the Enemy, may neither be consistent with prudence or good policy, and to delay it till after an Attack is begun would be too late, as the Contest will soon be decided for or against us after this happens.
Under this state of the Matter and to avoid putting an affair of so much Importance to a doubtful Issue, when under Providence, it may be reduced to a certainty; I submit it to the Wisdom of your Board; whether it might not be best to direct the Militia of certain Towns most contiguous to Dorchester and Roxbury, to repair to the Lines at those places with their Arms, Ammunition and Accourtrements instantly upon a Signal given.
If you approve of this, you will please to fix with General [John] Thomas (who waits on you for that purpose) upon the Signal to be given and Issue your Notices Accordingly.