Diamond Rock cave is popular with divers today, a triangular cave that has prolific quantities of sea fans. But Diamond Rock itself has a fascinating history, going back to the Napoleonic Wars of 1803 - 1815. British naval forces occupied Diamond Rock, the French held the island, and the three naval cannons the British placed on Diamond Rock allowed them to completely command the passage into Fort-de-France. Ships were forced to avoid the passage, but because of the prevailing winds and currents this meant it was not possible for large ships to enter Fort-de-France any other way. This resulted in an effective blockade, so effective that the British Admiralty declared Diamond Rock to be a Royal Naval vessel, the HMS Diamond Rock. (In 1815, after Naploeaon was captured and imprioned on St. Helena island, the Admiralty would name the nearby Ascension Island a "stone figate," the HMS Ascension.) After 18 months of attempts to take Diamond Rock, French forces were finally able to displace the British at the Battle of Diamond Rock on June 2, 1805. The British commander of the HMS Diamond Rock , Lieutenant Maurice, successfully got away, but was summarily court martialed (as the law dictated in any case when a captain loses his ship, regardless of the cause) but was honorably acquitted. One of the cannons that the French toppled into the sea has been reported to have been recently found by divers.
A great YouTube video of a swim through Diamond Rock cave.