Which French naval victory helped trap Cornwallis at Yorktown?

The Battle of the Chesapeake helped trap Cornwallis at Yorktown.

Fought on September 5, 1781, the Battle of the Chesapeake was a naval engagement between a French fleet commanded by the Comte de Grasse and a British fleet led by Sir Thomas Graves. Although neither side lost a ship, the French victory gave the allies control of the Chesapeake Bay at the critical moment of the Yorktown campaign.

The British fleet had been sent from New York to relieve Cornwallis, whose army was defending Yorktown, Virginia. After the French fleet maintained its position and the British withdrew, the British could not safely reinforce or evacuate Cornwallis by sea. French ships also helped protect the arrival of allied troops and supplies.

The battle is sometimes called the Battle of the Virginia Capes. Its strategic effect mattered more than the number of ships destroyed: without French naval control, the Yorktown siege might have ended very differently.