Four of the five French ships managed to break past the British blockade, taking shelter in the protected anchorage, which was only accessible through a series of complicated routes between reefs and sandbanks that were impassable without an experienced harbour pilot.

In December an adequate reinforcement was assembled with the provision of a strong battle squadron under Admiral Albemarle Bertie, which rapidly invaded and captured the Île de France.

Heavily laden East Indiamen travelled from ports in British India such as Bombay and Calcutta to the United Kingdom carrying millions of pounds of goods.

[1] Following the outbreak of the Napoleonic Wars in 1803, the British Admiralty had made the security of these routes a priority, and by 1807, the Dutch bases at the Cape of Good Hope and Java had been neutralised by expeditionary forces to prevent their use by enemy raiders.

[3] Four of these ships broke through the British blockade of the French coast, arriving in the Indian Ocean in the spring of 1809, where Hamelin dispersed them into the Bay of Bengal with orders to intercept, attack, and capture or destroy the heavily armed but extremely valuable convoys of East Indiamen.

[4] Commodore Josias Rowley was given command of the British response, a hastily assembled force composed mainly of those ships which happened to be available at the Cape of Good Hope in early 1809.

[10] Grand Port was an easily defensible natural harbour because the bay was protected from the open sea by a large coral reef through which a complicated channel meandered, known only to experienced local pilots.

Willoughby would then use a local man serving on his ship named John Johnson (referred to in some texts as "the black pilot"),[9] to steer through the channel and land troops near the town, distributing leaflets promising freedom and prosperity under British rule in an attempt to corrode the morale of the defenders.

[11] The first attack on Île de la Passe was launched on the evening of 10 August, with Staunch towing boats carrying over 400 soldiers, Royal Marines, and volunteer sailors to the islet under cover of darkness, guided by Nereide's pilot.

Pym joined Lambert later in the day and the frigates subsequently returned to the waters of Grand Port by different routes, confusing French observers from the shore as to British intentions.

[13][14] Willoughby was furious that Pym had assumed command of the operation without his permission and the officers exchanged angry letters, part of an ongoing disagreement between them that engendered mutual distrust.

Willoughby used his independent position to raid the coastline, landing at Pointe du Diable on 17 August on the northern edge of Grand Port with 170 men and storming the fort there, destroying ten cannon and capturing another.

[16] Marching south towards the town of Grand Port itself, Willoughby's men fought off French counterattacks and distributed propaganda pamphlets at the farms and villages they passed.

As Morice raised his colours again and followed Minerve, a large explosion blasted out of Île de la Passe, where the false French flag had ignited on a brazier as it was lowered and set fire to a nearby stack of cartridges, which exploded in the close confines of the fort.

[23] With the fort out of action and a significant number of her crew scattered in small boats in the channel, Néréide was alone and unable to block French entry to Grand Port.

[25] In the afternoon, Willoughby used mortars on Île de la Passe to shell the French squadron, forcing Duperré to retreat into the shallow harbour at Grand Port.

Willoughby subsequently sent officers into Grand Port on 21 August under a flag of truce, demanding the release of Victor, which he insisted had surrendered and should thus be handed over to the blockade squadron as a prize.

[30] Duperré also anticipated the arrival of reinforcements from Port Napoleon under Governor Charles Decaen at any time and could call on the support of soldiers and gun batteries on shore.

[31] At 8:00 pm, Duperré was seriously wounded in the cheek by shrapnel from grapeshot fired by Néréide; Ensign Vigoureux concealed his unconscious body under a signal flag and discreetly brought him below decks while Bouvet assumed command of the French squadron on board Bellone, placing Lieutenant Albin Roussin in charge of Minerve.

[40] He also had the rail removed between the foredeck and the quarterdeck of Minerve, and had iron hooks nailed to the freeboard below the starboard gangway so as to provide attachment points for additional guns, thus building a continuous second deck on his frigate where he constituted a complete second battery.

Accepting that Sirius was beyond repair, Pym removed all her personnel and military supplies, setting fire to the frigate at 9:00 am, shortly after Iphigenia had pulled beyond the range of the battery, using a cannon as an anchor after losing hers the previous day.

[54] During the morning, Duperré sent an official boarding party aboard Néréide, who wet the decks to prevent any risk of fire from the ships burning in the harbour and removed 75 corpses from the frigate.

On 23 August, Hamelin's squadron spotted and captured a British transport ship named Ranger, sent 24 days earlier from the Cape of Good Hope with 300 tons of food supplies and extensive naval stores for Rowley on Île Bourbon.

[55] On rounding the northern headlands of Île de France, Hamelin found he could make no progress against the headwinds and reversed direction, passing the western shore of the island and arriving off Grand Port at 1:00 pm on 27 August.

[57] On the morning of 28 August, Lambert received a message from Hamelin, promising to release all the prisoners under conditions of parole within one month if Île de la Passe and Iphigenia were both surrendered without resistance.

[59] Eager to support Pym's attack, Rowley immediately set sail in his frigate HMS Boadicea, with the transport Bombay following with two companies of the 86th Regiment of Foot to provide a garrison on any territory seized in the operation.

[60] Sighting a cluster of frigates around Île de la Passe, Rowley closed with the island before turning sharply when Vénus and Manche raised their colours and gave chase.

Withdrawing to Isle de France, Rowley requested that reinforcements be diverted from other duties in the region to replace his lost ships and to break the French blockade of Île Bourbon, led by Bouvet.

[59] Contemporary historian William James described British reaction to the battle as "that the noble behaviour of her officers and crew threw such a halo of glory around the defeat at Grand Port, that, in public opinion at least, the loss of four frigates was scarcely considered a misfortune.

[56] The battle attracted the attention of authors from both Britain and France, featuring in the 1843 novel Georges by Alexandre Dumas,[65] "Dead Reckoning" by C. Northcote Parkinson and the 1977 novel The Mauritius Command by Patrick O'Brian.