The battle, which lasted from 11–24 April 1809, was unusual in that it pitted a hastily-assembled squadron of small and unorthodox British Royal Navy warships against the main strength of the French Atlantic Fleet.

Sighted and chased by British blockade squadrons, the French were unable to escape the Bay of Biscay and eventually anchored in the Basque Roads, near the naval base of Rochefort.

Cochrane organised an inshore squadron of fireships and bomb vessels, including a converted frigate, and personally led this force into Basque Roads on the evening of 11 April.

In late 1808, the French learned that a British invasion of Martinique was in preparation, and so orders were sent to Willaumez to take his fleet to sea, concentrate with the squadrons from Lorient and Rochefort and reinforce the island.

[7] In the early morning of 23 February, Willaumez sent the dispatch schooner Magpye into Lorient with instructions for Troude to sail when possible and steer for the Pertuis d'Antioche near Rochefort, where the fleet was due to assemble.

Among the French fleet there was dissatisfaction that Willaumez had not attacked Stopford when he enjoyed numerical superiority, taking the opportunity to break out of the anchorage and pursue his objectives in the Caribbean.

Captain Jacques Bergeret was so incensed that he wrote a letter criticising Willaumez to the Minister of Marine Denis Decrès, and warning that the Aix Roads were highly vulnerable to British attack.

This boom measured 0.5 nautical miles (1,000 yd) long and 31.5 inches (80 cm) wide, weighted in place with 5 1/4 tons of anchors, and yet was installed so subtly that the British fleet did not observe it.

Gambier was concerned that an attack by French fireships on his fleet anchored in the Basque Roads might cause considerable destruction, and consequently ordered his captains to prepare to withdraw from the blockade at short notice should such an operation be observed.

[26] A number of officers in the fleet, in particular Rear-Admiral Eliab Harvey, volunteered to lead such an attack, but Gambier hesitated to act, failing to take soundings of the approaches or make any practical preparations for an assault.

Prime Minister Lord Portland's administration was concerned by the risk posed by the French fleet to the profits of the British colonies in the West Indies, and had determined that an attack must be made.

Cochrane, eldest son of the Earl of Dundonald, was an aggressive and outspoken officer who had gained notoriety in 1801 when he captured the 32-gun Spanish privateer frigate Gamo with the 14-gun brig HMS Speedy.

[29] In the frigates HMS Pallas and Imperieuse he had caused havoc on the French and Spanish coasts with relentless attacks on coastal shipping and defences including, most relevantly, operations in the Rochefort area.

[32][30] In addition, Cochrane was also well aware of the fury this decision would provoke in the naval hierarchy; the appointment of a relatively junior officer in command of such an important operation was calculated to cause offense.

[37] Gambier dismissed Harvey, sending him and his 80-gun HMS Tonnant back to Britain in disgrace to face a court-martial, and then ordered Cochrane to begin preparations for the attack.

A number of chasse-marées carrying tar and resin perfect for this role had been captured by the blockade, and Cochrane requisitioned eight military transport ships from the fleet reserve for conversion using these materials.

[41] On three of the vessels Cochrane had loaded 1,500 barrels of gunpowder, topped by hundreds of artillery shells and thousands of grenades to create an explosion ship, a floating bomb of his own design intended to detonate right in the middle of the French line.

[42] During this process an attack by French boats on the fireships was driven off, with two British sailors killed and one wounded,[38] and on 5 April Cochrane reconnoitered the approaches to Aix Roads, firing shots at the forts and fleet to gauge their responses.

[43] He subsequently wrote to Mulgrave suggesting that with an expeditionary force of 20,000 he could seize the defences overlooking the anchorage, sink blockships in the channel and thereby permanently deprive the French of one of their most important naval bases, although his letter was ignored.

[51] As night approached it became clear that the wind, although blowing in the correct direction, was too strong to allow the fireships to be chained together in squadrons as planned, and each was instructed to operate independently.

Shells from Aetna and thousands of rockets burst amid the confusion as the forts and all ships fired their guns at threats real and imagined; "a scene ... peculiarly awful and sublime.

Finally the fleet sailed at 10:45, but at 11:30 Gambier ordered a halt after only 3 nautical miles (5.6 km), and the ships anchored once more near Île-d'Aix while the admiral conducted a conference with his captains.

[74] Cochrane had forced Gambier's hand: despite his desire to avoid combat, the admiral could not allow one of his frigates to fight the entire French fleet single-handed, and reluctantly he instructed the large frigate HMS Indefatigable, the smaller Emerald, Unicorn, Aigle and Pallas and the ships of the line Valiant and Revenge, the latter now commanded by Captain Alexander Robert Kerr, to join with the inshore squadron, enter the Aix Roads and support Cochrane.

[79] Although Gambier had no intention of risking his fleet in the narrow waters of Basque Roads, he had permitted three more transports to be fitted out as fireships, and at 17:30 these were led into the anchorage by Stopford in Caesar, accompanied by Theseus and several launches equipped to fire Congreve rockets.

At this point six surviving French ships; Océan, four of the line and the frigate Indienne, remained aground close to the mouth of the Charente, while the remainder of the fleet had escaped upriver to secure anchorages.

[80] During the night the wind blew from the land, rendering a fireship attack impractical, and so the British contented themselves with setting Ville de Varsovie and Aquilon on fire, both ships determined by John Bligh on Valiant, over Cochrane's objections, to have been damaged beyond repair.

The French sailors made significant efforts to retrieve these ships over the following days; on 16 April Indienne was deemed too damaged to be saved, abandoned, and set on fire.

[97] The battle was undoubtedly a victory for the British; four French ships of the line (Ville de Varsovie, Tonnere, Aquilon and Calcutta) and a frigate (Indienne) were destroyed and much of the remainder of the Brest fleet badly damaged and requiring extensive repairs; Océan and Foudroyant were in a particularly poor state.

The court was convened on 26 July; the inquiry panel president was Admiral Sir Roger Curtis and his deputy was William Young, both friends of Gambier and political opponents of Cochrane.

For example, William Laird Clowes, wrote in 1901 that "there can be no question that affair of Aix Road was mismanaged by the Admiralty at home and by the Admiral on the spot"[97] and that "a great naval commander never loses an occasion to attack when conditions are favourable to him.