Which naval battle helped prevent British relief of Cornwallis at Yorktown?

The Battle of the Chesapeake helped prevent British relief of Cornwallis at Yorktown.

Fought on September 5, 1781, the battle pitted a British fleet commanded by Thomas Graves against a French fleet led by the Comte de Grasse. Although neither side lost a ship, the British fleet withdrew after the engagement and failed to break French control of the Chesapeake Bay.

That naval result was crucial to the Yorktown campaign. French ships blocked the sea route by which British forces might have reinforced or evacuated Cornwallis’s army. French naval support also helped keep the allied siege supplied while American and French troops tightened their land lines around Yorktown.

The battle is sometimes overshadowed by the later surrender, but Yorktown depended on control of both land and water. The victory demonstrates why the 1781 campaign was an international Franco-American operation rather than an exclusively American action.