(September 5, 1781), in the American Revolution, French naval victory over a British fleet that took place outside Chesapeake Bay. The outcome of the battle was indispensable to the successful Franco-American Siege of Yorktown (Yorktown, Siege of) from August to October.

In late summer 1781 Lord Cornwallis (Cornwallis, Charles Cornwallis, 1st Marquess and 2nd Earl, Viscount Brome, Baron Cornwallis of Eye) led the main British army of the South onto the Yorktown Peninsula, Virginia, where he confidently awaited rescue by reinforcements from the British fleet. In the meantime the French admiral comte de Grasse (Grasse, François-Joseph-Paul, comte de, marquis de Grasse-Tilly) proceeded with his entire fleet of 24 ships from the West Indies to Chesapeake Bay.

Sailing from New York, a British fleet of 19 ships under the command of Admiral Thomas Graves confronted the French at Virginia Capes on September 5. Only the leading squadrons of the two fleets engaged in moderate fighting in the late afternoon. Although British losses were heavier, the contest was by and large undecided, and the two partly becalmed fleets drifted along parallel courses for the next three days without incident. Then, reinforced by additional vessels and siege guns from Newport, Rhode Island, the French sailed back into Chesapeake Bay to take final control of the harbour, while the British fleet returned to New York. British naval historian Sir William M. James labeled this the “decisive battle of the war,” one that sealed the fate of Cornwallis and of the British cause in America.