The Battle of Diamond Rock took place between 31 May and 2 June 1805 during the Napoleonic Wars. It was an attempt by Franco-Spanish force dispatched under Captain Julien Cosmao to retake Diamond Rock, at the entrance to the bay leading to Fort-de-France, from the British forces that had occupied it over a year before.

The French in Martinique had been unable to oust the defenders from the strategically important rock, and the British garrison was able to control access to Fort-de-France Bay, firing on ships attempting to enter it with guns they had placed on the cliffs. The arrival of a large combined Franco-Spanish fleet in May changed the strategic situation. The French commander, Pierre de Villeneuve, had vague orders to attack British possessions in the Caribbean, but instead waited at Martinique for clearer instructions. He was finally persuaded to authorise an assault on the British position, and a Franco-Spanish flotilla was dispatched to storm the rock. Already short of water, the defenders held on in the summit for several days, while the French, who had neglected to bring scaling ladders, could make little headway.

The British, short of both water and ammunition, eventually negotiated the surrender of the rock after several days under fire. As Diamond Rock was legally considered a Royal Navy vessel, and the commander was legally "captain" of it, after repatriation, he was tried by court-martial (as the law dictated in any case where a captain loses his ship, regardless of the cause), but was honourably acquitted.