One of the most unusual battlefields of the Napoleonic Wars was located in the Caribbean, southwest of the island of Martinique. It is a basaltic rock located in the channel of Saint Lucia, about three kilometers from Pointe Diamant, which the British and the French fought over, seizing it from each other several times between 1803 and 1815. Today it is uninhabited, except for several colonies of seabirds and an endemic species believed to be extinct, a snake variety called Erythrolamprus cursor. We are talking about Rocher du Diamant.

You don’t need to know French to understand the meaning of that name. It is called Diamond Rock because of the reflections its stone walls project when exposed to sunlight at certain times of the day, resembling that precious stone. In reality, it is a volcanic neck or plug, a type of relief formed by the hardening of lava within a flow, vein, or even the crater of an active volcano. In this case, it is estimated to have formed a million years ago.

As with the other fifty or so islets surrounding Martinique, Diamond Rock evolved in isolation, covered with hedges and cacti, receiving more sunlight than the main island and less precipitation, giving it a longer dry season. All of this, combined with the absence of human occupation, has allowed colonies of seabirds such as terns and gannets to establish themselves there, in addition to promoting the survival – at least until 1968, when the last specimen was sighted – of the mentioned snake.

However, in addition to these natural characteristics, there are other more mundane ones: the strategic ones, as the crag occupies a privileged position north of the channel of Saint Lucia, providing perfect conditions to control navigation between the island of Martinique and its southern neighbor, Santa Lucia. In the context of the Napoleonic conflict of the early 19th century, this was of obvious interest to the contenders, entangled in disputing control over the Caribbean island arc.

Consequently, the British occupied the islet. It was at the initiative of Rear Admiral Sir Samuel Hood, a veteran of several conflicts who had been entrusted with the mission of blocking the bays of Saint Pierre and Fort Royal (future Fort-de-France, the island’s capital) and Saint Pierre, in Martinique. Anchored off the latter aboard the HMS Centaur, lookouts spotted a schooner escorting a sloop, and Hood sent to capture the second while the Centaur took care of the first. After a long chase, the schooner was captured and turned out to be a privateer ship called Ma Sophie.

Although its crew had thrown overboard its eight cannons to prevent them from falling into enemy hands, the ship passed into the service of the Royal Navy as an auxiliary under the command of Lieutenant William Donnett. He was tasked with monitoring the channel between Martinique and Rocher du Diamant, periodically landing on the islet to collect callaloo (a plant boiled to combat scurvy) and a thick grass used by sailors to make hats by weaving it.

In January 1804, taking advantage of the good weather and calm seas, Hood decided to establish a fortified position at the top of Rocher du Diamant, building stone parapets behind which he placed two 18-pound cannons and leaving a garrison of over a hundred men under the command of Lieutenant James Wilkes Maurice. The crag acquired the status of a stone frigate, as if it were a ship of His Gracious Majesty, to the point that it was given an ad hoc name: HMS Diamond Rock.

The reason for such an extravagant initiative, which would give rise to a tradition over time to the present day, was due to a technicality: the Royal Navy had no authority to command on land, so Rocher du Diamant was given the consideration of a sloop-of-war, a type of vessel with a single gun deck and up to eighteen guns.

Later, Hood reinforced the islet with three 24-pound pieces, two at the top and the third – a carronade – at the landing place, also assigning the HMS Fort Diamond, a cutter (a small single-masted vessel with about thirty crew members and six cannons) commanded by Lieutenant Thomas Forest, as support. This was convenient because an explosion, for unknown reasons, sent Ma Sophie to the bottom, with only one sailor surviving.

The works were considered finished on February 7, and the Admiralty was officially informed, which meant that, from then on, personnel from any British ship passing by the crag had to perform the protocol salute in a standing position. Discipline, in fact, was maintained as in any other place, and in 1805 a lieutenant was sent to Plymouth to face a court-martial for having eaten with his soldiers on top of the crag, outside the cave designated as the mess hall.

At Rocher du Diamant, or, to be precise, HMS Diamond Rock, the Union Jack was already flying; the caves that pierced the rock served as barracks for the troops – officers lived in tents – and one located at the base was reserved for a field hospital, frequently used due to tropical diseases. Supplies were hoisted to the top in baskets brought by ships through pulleys, although to increase provisioning, a herd of goats and a flock of chickens and guinea fowl were relocated there.

A danger loomed shortly after. A group of escaped slaves who had reached the islet reported that a French lieutenant colonel of engineers was preparing to install a mortar battery on the coast to bombard Rocher du Diamant. Hood offered the slaves enlistment – England was already firmly opposed to the slave trade – in exchange for guiding a force to that place. They accepted, and a score of marines led by Lieutenant Reynolds disembarked from the HMS Centaur at midnight, covered four kilometers, and captured the engineer and seventeen soldiers.

Apparently, the French did not have more engineers, so the possibility of bombarding the islet vanished. But they found other prey. In June 1804, while the HMS Fort Diamond was in Saint Lucia on a supply mission, a couple of boats from a French schooner boarded it at night. Lieutenant Benjamin Wescott, who was temporarily in command of the lost cutter, was subjected to a court-martial held in Antigua, aboard the frigate HMS Galatea, and expelled from the Royal Navy; three years later, he became a U.S. citizen.

Nevertheless, Rocher du Diamant still posed a problem for the navigation of any French vessel attempting to pass through the channel, as they either exposed themselves to its powerful artillery – with up to seventy kilometers of visibility – or faced the dangerous currents and winds between the islet and Martinique. That’s why one of the goals of Admiral Pierre-Charles Villeneuve on his trip to America in 1805 was to regain Rocher du Diamant. It was secondary, of course, since the main goal was to move the Royal Navy away from Europe to clear the way for Bonaparte’s crossing of the English Channel and the invasion of Britain.

However, Admiral Louis Thomas Villaret-Joyeuse, the general governor of Martinique and Santa Lucia, saw the arrival of the combined Franco-Spanish fleet of sixteen ships as a great opportunity to end that “symbol of insolence at the gates of Martinique” and convinced Villeneuve, who had already been prepared for it by Napoleon. Consequently, he sent a division composed of the ships Pluton and Berwick, the frigate Syrène, and the corvettes Fine and Argus; it was led by Captain Julien Marie Cosmao-Kerjulien.

After ensuring a blockade that prevented reinforcements, four longboats and four canoes, half provided by the French squadron and the other half by the Spanish squadron, approached the islet during the early morning of May 31, 1805, and landed an invasion force. The British managed to hold the French in the lower area of the crag, preventing them from advancing, but in return, they had to disable their lower cannons and saw their rivals seize the water depots – broken in the fighting, anyway – and supplies, meaning they could not resist.

On the following night, after a hard preparation of the terrain through naval bombardment and with the arrival of reinforcements equipped with ladders and ropes, the attackers were able to climb at multiple points and force the surrender of the enemy, which became official on June 3. The one hundred and seven prisoners were repatriated to Barbados, and Lieutenant Maurice faced a court-martial for the loss of his ship (the islet), although he was exonerated and even obtained command of the brig HMS Savage.

Although they suffered twenty dead and forty wounded compared to only two dead and one wounded British, Villeneuve described the capture of the crag as a “beautiful feat of arms, due to the difficulties it presented and the combination of defense means that the enemy had gathered“, praising Cosmao-Kerjulien (who would later distinguish himself in the battles of Cape Finisterre and Trafalgar, being one of the few French sailors praised by the Spaniards, who even appointed him Grandee of Spain).

Following the plan, as soon as Nelson arrived in the Caribbean, the French admiral returned to Europe; General Reille complained that during that time, no large island had been attacked (only fifteen merchant ships were captured, and it was the Spaniard Gravina who did it).

Therefore, seventeen months later, the islet belonged to France again and remained so until 1809, when the British invaded Martinique and Guadeloupe. Admiral Alexander Cochrane and Lieutenant General George Beckwith led a force of twenty-nine ships and ten thousand men, quadrupling the defenders of the island, and occupied it relatively easily, in less than a month, before Villaret-Joyeuse agreed to surrender on February 24. Of course, the surrender also implied the delivery of Rocher du Diamant, which once again passed into the hands of His Gracious Majesty.

It was not until the end of the Napoleonic Wars in 1815 that French control was restored, which still continues today as an overseas department. As we mentioned at the beginning, it is uninhabited; after all, its tiny surface (three hundred and twenty-four meters long by two hundred and ninety wide) and its rugged topography (one hundred and seventy-five meters high) make even its tourist exploitation difficult, except for the visits of divers to what they consider one of the best dive sites in Martinique. Birds and snakes will appreciate it.

This article was first published on our Spanish Edition on January 8, 2024. Puedes leer la versión en español en Roca del Diamante, el peñón caribeño con categoría de buque de la Royal Navy que se disputaron británicos y franceses


Mark Adkins, The Trafalgar companion. A guide to history’s most famous sea battle and the life of Admiral Lord Nelson | James Henderson, Frigates-sloops & brigs | Mark Adkins, The war for all the oceans. From Nelson at the Nile to Napoleon at Waterloo | Auguste Thomazi, Les marins de Napoléon | Wikipedia

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