Yorktown
On September 6, General Clinton wrote a letter to Cornwallis, telling him to expect reinforcements. Received by Cornwallis on September 14, this letter may have been instrumental in the decision by Cornwallis to remain at Yorktown and not try to fight his way out, despite the urging of Banastre Tarleton to break out against the comparatively weak Lafayette. General Washington, after spending a few days at Mount Vernon for the first time in years, arrived in the camps outside Yorktown on September 17. That same day, the British military leadership in New York held a council, in which they agreed that Cornwallis could not be reinforced until they had regained control of the Chesapeake. Historian Richard Ketchum describes the decision of the council as leaving Cornwallis "dangling in the wind." One day earlier, Cornwallis wrote a desperate plea for help: "I am of the opinion that you can do me no effectual service but by coming directly to this place." Before dispatching the letter on the 17th, Cornwallis added, "If you cannot relieve me very soon, you must prepare to hear the worst".
Washington, Rochambeau, and de Grasse then held council aboard de Grasse's flagship Ville de Paris to finalize preparations for the siege; de Grasse agreed to provide about 2,000 marines and some cannons to the effort. During the meeting, de Grasse was convinced to delay his departure (originally planned for mid-October) until the end of October. Upon the return of the generals to Williamsburg, they heard rumors that British naval reinforcements had arrived at New York, and the French fleet might again be threatened. De Grasse wanted to pull his fleet out of the bay as a precaution, and it took the pleas of Washington and Rochambeau, delivered to de Grasse by Lafayette, to convince him to remain.
The siege formally got underway on September 28. Despite a late attempt by Cornwallis to escape via Gloucester Point, the siege lines closed in on his positions and the allied cannons wrought havoc in the British camps, and on October 17 he opened negotiations to surrender. On that very day, the British fleet again sailed from New York, carrying 6,000 troops. Still outnumbered by the combined French fleets, they eventually turned back. A French naval officer, noting the British fleet's departure on October 29, wrote, "They were too late. The fowl had been eaten."
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