In the Battle of Sandwich on August 24, 1217 a Plantagenet English fleet commanded by Hubert de Burgh attacks a Capetian French armada led by Eustace the Monk and Robert of Courtenay.

The English capture the French flagship and most of the supply vessels, forcing the rest of the French fleet to return to Calais.

The naval battle takes place off Sandwich, Kent on the English coast during the First Barons' War.The French fleet is attempting to bring supplies to Prince Louis, later King Louis VIII of France, whose French forces hold London at this time.

The English vessels attack from windward, seizing Eustace's ship, making Robert and the knights prisoner and killing the rest of the crew.

Eustace, a notorious pirate, is executed after being taken prisoner.

The battle convinces Prince Louis to abandon his effort to conquer England and the Treaty of Lambeth is signed a few weeks later.