Which naval battle in 1781 helped prevent British relief of the American siege at Yorktown?

The Battle of the Chesapeake helped prevent British relief of the American siege at Yorktown in 1781.

The battle took place on September 5, 1781, near the entrance to the Chesapeake Bay. A French fleet commanded by Admiral François Joseph Paul de Grasse fought a British fleet led by Rear Admiral Thomas Graves. Although the engagement was tactically inconclusive, the British fleet withdrew and did not break the French control of the bay.

That naval result was strategically decisive. Cornwallis’s army at Yorktown depended on the possibility of evacuation or reinforcement by sea. With the French fleet controlling access to the bay, Washington and French commander Rochambeau could maintain the siege and bring Cornwallis to surrender on October 19.

The battle is also known as the Battle of the Virginia Capes. It was not fought directly at Yorktown, and it involved ships offshore rather than the land armies surrounding Cornwallis.