The Battle of Diamond Rock took place between 31 May and 2 June 1805 during the Napoleonic Wars, when a Franco-Spanish force dispatched under Captain Julien Cosmao was able 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.

Julien Marie Cosmao-Kerjulien was a French Navy officer, admiral, best remembered for his role in the Battle of Trafalgar.