http://en.wikipedia.org/wiki/François_Joseph_Paul_de_Grasse
Battle of Chesapeake and Yorktown Campaign
[Degrasse] came to the aid of Washington and Rochambeau's Expédition Particulière, setting sail with 3,000 men from Saint-Domingue. De Grasse landed the 3,000 French reinforcements in Virginia, and immediately afterward decisively defeated the British fleet in the Battle of the Chesapeake in September 1781. He drew away the British forces and blockaded the coast until Lord Cornwallis surrendered, ensuring the independence of the United States of America.