Allemand's expedition of 1805, often referred to as the Escadre invisible (invisible squadron) in French sources, was an important French naval expedition during the Napoleonic Wars, which formed a major diversion to the ongoing Trafalgar campaign in the Atlantic Ocean. With the French Mediterranean Fleet at sea, Emperor Napoleon I hoped to unite it with the French Atlantic Fleet and together form a force powerful enough to temporarily displace the British Royal Navy Channel Fleet for long enough to allow an invasion force to cross the English Channel and land in Britain. In support of this plan, the French squadron based at Rochefort put to sea in July 1805, initially with the intention that they would join the Atlantic Fleet from Brest. When this fleet failed to put to sea, the Rochefort squadron, under Counter-admiral Zacharie Allemand, went on an extended raiding cruise across the Atlantic, both to intercept British trade left lightly defended by the concentration of British forces in European waters and with the intention of eventually combining with the French Mediterranean Fleet then blockaded in Spanish harbours.
On 25 September, Allemand achieved a major success when his squadron, while waiting for a convoy from the Leeward Islands, encountered a seven-ship convoy from the island of Saint Helena. The convoy's commander, Captain Daniel Woodriff in the fourth rate , sought to interpose his ship between the French squadron and his convoy and was captured after a fierce battle. All except one of convoy escaped, and by deliberately drawing the French away from his own convoy's direction, he had saved the Leewards Islands convoy from attack as well. After the battle, Allemand was forced to conduct repairs at Tenerife, sailing again on 17 October, four days before the French Mediterranean Fleet was destroyed at the Battle of Trafalgar. With the planned invasion impossible, Allemand began commerce raiding in the Eastern Atlantic, capturing 43 merchant ships during his cruise and successfully disrupting the British blockade of Cádiz. This had an unintended but significant effect on the Atlantic campaign of 1806, resulting eventually in the Battle of San Domingo in February 1806. Allemand returned to Rochefort on 23 December, having not lost a single ship during the expedition.
Trafalgar campaign
In March 1805, the French Mediterranean Fleet sailed from Toulon under Vice-Admiral Pierre-Charles Villeneuve for an extended cruise to the West Indies, ultimately under orders to link with the French Atlantic Fleet based at Brest. Together these fleets would stage a major operation in the English Channel, driving off the Royal Navy's Channel Fleet and allowing a fleet of landing barges to land on the southern coast of England as the first move in an invasion of Britain.Mostert, p. 439 Arriving at Martinique on 14 May, Villeneuve waited for reinforcements from the Atlantic fleet, only to be informed on 2 June that they had failed to leave port. Despite repeated orders issued to the Atlantic fleet instructing them to sail to Martinique, Vice-Admiral Honoré Ganteaume had failed in his one effort to break out of Brest during March and then given up. His entire fleet ultimately remained in port throughout the Trafalgar campaign.The Campaign of Trafalgar, Gardiner, p. 99 On 7 June Villeneuve learned of the arrival in the Caribbean of the British Mediterranean Fleet under Vice-Admiral Lord Nelson and hastily sailed back to Europe, eventually sheltering in the Spanish harbour of Vigo after an encounter on 22 July with a British fleet under Sir Robert Calder at the Battle of Cape Finisterre, in which two of his ships were captured. In the aftermath of the spring campaign, both Nelson and Calder returned to Britain, leaving only relatively small squadrons off the French and Spanish coasts.The Campaign of Trafalgar, Gardiner, p. 130
Despite delays to his plan, Napoleon had pressed ahead with preparations for his planned invasion of Britain; an army of 200,000 men was assembling at Boulogne for the invasion, and orders continued to insist that the fleets under Villeneuve and Ganteaume put to sea.Mostert, p. 469 Also ordered to sail was the squadron based at the Atlantic port of Rochefort, led by Counter-admiral Zacharie Allemand. Allemand's squadron consisted of the powerful 120-gun ship Majestueux, three other ships of the line and several frigates and brigs, forming a significant force in its own right and a valuable addition to any battle fleet. Allemand was ordered to cruise off the southern coast of Cornwall, awaiting the combined fleets of Villeneuve and Ganteaume and their descent into the Channel. If this force did not materialise, Allemand was subsequently ordered to the Bay of Biscay to join up with Villeneuve on his route northwards and should this too fail then he was to conduct an extended commerce raiding operation in the Atlantic to take advantage of the concentration of British forces off Europe and the consequent exposure of British trade.James, Vol. 4, p. 148
Bay of Biscay Allemand sailed from Rochefort on 16 July while the blockade squadron under Rear-Admiral Charles Stirling was out of position, rapidly escaping the coast into the Atlantic. On 17 July, the squadron outran and captured the British corvette or sloop-of-war , rated as 16 guns but actually carrying 24. Ranger's crew had observed the approaching French squadron from some distance, and Commander Charles Coote had ordered that once their capture was inevitable, the crew were to cause as much damage as possible to their vessel to deny its use to the French. So successful were these efforts that Allemand was forced to burn Ranger once her crew had been removed as prisoners of war. Allemand subsequently reached his first station, off The Lizard, the day after capturing Ranger. There he waited in vain for the fleet under Ganteaume, which had never departed Brest. Following his instructions, Allemand then sailed for the Bay of Biscay, where he was to meet the fleet under Villeneuve that had been ordered north to join with Ganteaume. He passed southwards during July and was in the region of Cape Finisterre on 22 July: later records show that he was close enough to the site of the Battle of Cape Finisterre to have participated in the engagement if he had been aware that it was under way.Clowes, p. 118 News of Allemand's presence reached Villeneuve early in August and on 5 August he despatched the frigate in search of the Rochefort squadron. Didon was followed on 9 August by the main fleet, including 29 ships of the line and associated frigates and corvettes. Villeneuve passed up the Spanish coast, anchoring off the village of Zerez, near Ferrol, on 10 August and departing the following day in a west by northwest direction. On 13 August the fleet was spotted by the frigates under Captain Edward Brace and under Captain Thomas Dundas, who were forced to flee a French detachment sent in pursuit, losing sight of the enemy on 14 August as Villeneuve's main force continued to the northwest.James, Vol. 4, p. 17
While Villeneuve was searching for Allemand, the Rochefort squadron was passing south along the Spanish coast in search of Villeneuve, anchoring at Vigo on 16 August without having seen any sign of the combined fleet. Villeneuve had not left instructions at Vigo for the Rochefort squadron and Allemand was uncertain where his superior was intending to sail to.Clowes, p. 124 One of Villeneuve's scouting frigates meanwhile had spoken with a Danish ship that reported a fleet of 25 British ships of the line actively searching the region for the combined fleet. When on the evening of 14 August Villeneuve's scouts sighted the ship of the line under Captain Edward Griffiths, the frigate and the captured Didon to the west, the French admiral assumed they were an advance guard of this British fleet and turned away to the south, the impression encouraged by frantic signals raised by Dragon.Clowes, p. 121 In fact, these ships were the only British forces in the region. The Danish ship had been boarded by Dragon earlier in the day and her crew deliberately fed misinformation about British strength. When the French scouts sighted Dragon, the presence of the captured Didon and Captain Griffiths' signals, that were made to an expanse of empty sea beyond the visible horizon on the French ship, successfully misled the French admiral into fleeing a non-existent fleet.James, Vol. 4, p. 18
Bypassing Vigo on his flight southwards, Villeneuve put into the Southern Spanish fleet base of Cádiz on 20 August. By abandoning his efforts to reach the English Channel, Villeneuve was in effect abandoning the entire invasion strategy and, when news of Villeneuve's retreat reached him, Napoleon decided to formally abandon the invasion of Britain, marching the army at Boulogne south to the Austrian border.Mostert, p. 471 Without instructions from his superior, and with no idea where the main French fleet was, Allemand spent much of August off the Spanish coast before deciding to turn to the third aspect of his orders, the disruption of British trade.Clowes, p. 169
The Calcutta convoy
The threat posed by the fleets in Brest and Cádiz was stretching the Royal Navy, and convoy escorts were weaker than usual as so many vessels had been diverted to the blockade fleets needed to watch French and Spanish movements. As a result, there were a number of independently sailing merchant ships in the Bay of Biscay and Allemand encountered and captured three on his journey north into the area later known as the Western Approaches. From the prisoners taken out of these ships, the French admiral learned that a large convoy was due from the West Indies, protected only by a single ship of the line, . This rich prize would be a major success for Allemand and his squadron cruised the Western Approaches in anticipation of its arrival during September 1805.
At 12:00 on 25 September at , Armide, an outlying frigate from Allemand's squadron, spotted sails to the southeast. Closing to investigate, these sails were identified as a small British convoy, not the expected force under Illustrious but another convoy from Saint Helena, consisting of the East Indiaman Indus, two whalers, three small merchant ships, the slow merchant vessel Brothers and the 50-gun fourth rate ship . The convoy had departed Saint Helena with seven ships on 3 August, and made fast time northwards until 14 September when it was joined by Brothers, which had been blown out of the Illustrious convoy by Atlantic gales several days earlier. Brothers was a heavily laden ship that sailed poorly, and as a result the entire Saint Helens convoy was severely delayed. When lookouts on Calcutta sighted the sails to the northwest, Captain Daniel Woodriff was not immediately alarmed. He was expecting the Illustrious convoy from that direction, and knew that a number of British squadrons were at sea. Throughout the afternoon and the following night the sails closed with his squadron until at 11:00 on 26 September they were close enough for Woodriff to make the Royal Navy secret recognition signals.James, Vol. 4, p. 147