The 'Battle of Dakar was the naval core of the undertaking known to the British as 'Menace' (31 August/29 September 1940), and was a British and Free French attempt to take the strategically important Vichy French port of Dakar in the Senegal region of French West Africa (23/25 September 1940).

After the 25 June implementation of the 22 June armistice which suspended hostilities between France and Germany, there was considerable confusion as to the allegiance of the various French colonies and mandated territories comprising the African federation (Dahomey, French Guinea, French Sudan, French Togo, Ivory Coast, Mauritania, Niger, French West Africa and Upper Volta). Dakar, the capital of French West Africa, was the third largest port in the French empire, and the capital of Pierre François Boisson, who had been appointed as the Vichy French high commissioner of Black Africa (French West Africa and French Equatorial Africa). Boisson in fact controlled only French West Africa as French Equatorial Africa was on the verge of rallying to the Free French cause under Général de Brigade Charles de Gaulle as a result of the 'Battle of Gabon' 1 between 8 and 12 November. The battle resulted in de Gaulle’s Free French seizing from the Vichy French forces first Libreville, the capital of Gabon, and then all of French Equatorial Africa.

Meanwhile, in French West Africa, Boisson tried and generally succeeded in applying a policy of strict neutrality, but the presence of powerful French warships in Dakar caused the British considerable concerns which dovetailed with the ambitions of de Gaulle to enlarge his Free French 'empire'.

Before the Franco-German armistice, the French fleet in the Mediterranean had counterbalanced the Italian navy in that vital theatre, leaving the Royal Navy free to concentrate on the German warships in the North Sea and Atlantic Ocean. That the French fleet might fall into German hands after June 1940 then led to the British 'Catapult' attack on the French fleet at Mers el Kébir in July 1940, but while this attack suppressed a possible threat to British superiority in the Mediterranean, it did nothing to encourage individual units to join the UK-based Free French.

de Gaulle believed that he could persuade the Vichy French forces in West Africa to join the Allied cause, even though all the available intelligence suggested strongly that this was not the case. The political consequences of a change of allegiance by another Vichy French colony would in themselves be a major advantage for the Allies, but there would also be a significant military benefit: it would deny the Germans any chance to base U-boats and/or surface vessels in the port of Dakar for forays against Allied convoys in the South Atlantic, and as Allied base Dakar was much better situated for the naval forces protecting the convoys sailing round West Africa than Freetown, the base in Sierra Leone which the Allies were currently using.

Another factor militating for the seizure of Dakar was the fact that much of the gold reserves of the Banque de France and the Polish government-in-exile was stored in Dakar.

The Allied 'Menace' plan had been finalised and the operation authorised on 27 August. The invasion force sailed in three groups under the command of Vice Admiral J. H. D. Cunningham, previously commander of the 1^st Cruiser Squadron in Admiral Sir Charles Forbes’s Home Fleet: that from Scapa Flow in the Orkney islands group comprised three transport vessels escorted by the light cruiser Fiji and three destroyers, that from the Clyde river of the heavy cruiser Devonshire, one destroyer, three Free French sloops and one trawler, and that from Liverpool of three transports escorted by three destroyers. Major General N. M. S. Irwin’s ground force comprised 4,200 British troops (centred on the 101^st Royal Marine Brigade) and 2,700 Free French troops embarked in the Free Dutch liners Pennland and Westernland, and the Free Polish liner Sobieski. The ground force’s heavy equipment and other specialised stores (including motor transport) sailed with a mercantile convoy to Freetown, where the invasion force was to gather for the operation proper.

The orders given to this Allied force were first to seek a negotiated settlement with the Vichy French high commissioner, and only if this was unsuccessful to use force to take the port and city.

Naval support was vested in Cunningham’s Force 'M', which comprised the new fleet carrier Ark Royal, the old battleships Barham and Resolution, the heavy cruisers Australia (replacing Fiji which had been torpedoed by U-32 off the Hebrides islands group on 1 September and had to return for repairs), Cumberland and Devonshire, the light cruisers Delhi and Dragon, the destroyers Echo, Eclipse, Escapade, Faulknor, Foresight, Forester, Fortune, Fury, Greyhound and Inglefield, the escort/patrol vessels Bridgewater, Commandant Dominé, Commandant Duboc, Houduce, Milford and Savorgnan de Brazza, and the Dutch liners Pennland and Westernland serving as transports.

Part of this naval force was supplied by Vice Admiral Sir James Somerville’s Gibraltar-based Force 'H', whose contribution took the form of Ark Royal, Resolution, Faulknor, Foresight, Forester, Fortune. Fury and Greyhound, which departed Gibraltar on 6 September to rendezvous with the convoy, the heavy cruisers Cornwall and Cumberland and the sloops Bridgewater and Milford arriving from the South Atlantic before proceeding to the assembly point at Freetown.

The Vichy French naval forces present at Dakar under the command of Contre-amiral C. J. L. Bourragué were the battleship Richelieu, the light cruisers Georges Leygues and Montcalm, the destroyers Audacieux, Fantasque, Malin and Hardi, the escort/patrol vessels Calais, Commandant Rivière, d’Entrecasteaux, d’Iberville, Gazelle and Surprise, the auxiliary cruisers El Kantara, El Mansour, Schoelzer and Ville d’Oran, the submarines Ajax, Bévéziers and Persée, and the merchant ships Porthos and Tacouna.

One of the most advanced warships in the French navy, Richelieu had departed Brest on 18 June before the Germans reached the port despite the fact that she was only about 95% complete. She had been damaged by air-launched torpedo attack on 8 July. Until the establishment of the Vichy French government, the British light carrier Hermes had been operating with the French forces in Dakar as the French had no such ships of their own, but on the establishment of the Vichy French regime had been ordered to sea and remain on watch. Joined by Australia, her bombers had attacked Richelieu, hitting her with one torpedo. When the Allied force arrived, therefore, the French battleship was immobilised but still able to function as a very powerful floating gun battery.

Three submarines and several lighter ships had been there with her.

A note of confusion had been added to the overall situation on 11 September when Cunningham received a report that the Vichy French light cruisers Georges Leygues, Gloire and Montcalm, escorted by three large destroyers, were believed to be in the area after passing westward through the Strait of Gibraltar after departing Toulon in the south of France. There was considerable confusion in British naval circles (in the UK, at Gibraltar and with Force 'M') about the likely destination of the Vichy French squadron and how the problem was to be overcome, but the matter resolved itself when Georges Leygues and Montcalm, as well as the three destroyers, put into Dakar, Gloire having been shepherded into Casablanca after suffering mechanical problems. The light cruiser Primauguet, patrolling from Dakar, was also persuaded to put into Casablanca.

The French squadron had in fact been destined for Libreville in Gabon to bolster the local forces against Free French leanings in central Africa, Chad having defected recently to the Allied cause, and its fortuitous presence in Dakar did much to strengthen the pro-Vichy French stance of the Senegalese administration, already confident of its ability to resist British naval pressures thanks to the availability of Richelieu.

The British and Free French forces reached Freetown, just to the south of Dakar, on 14 September and completed their final preparations before heading to the north in three groups between 19 and 21 September.

On 23 September, Fleet Air Arm aircraft dropped propaganda leaflets on the city of Dakar. Then, two Free French Caudron C.272 single-engined light aircraft and a Fairey Swordfish single-engined bomber carrying three Free French officers flew off Ark Royal and landed at the airport, but their crews were immediately taken prisoner. On one of the prisoners was found a list of Free French sympathisers in Dakar, whom the Vichy French authorities promptly seized. A boat with representatives of de Gaulle entered the port but was received with gunfire. British aircraft were also engaged by the anti-aircraft guns of Richelieu and the attentions of a Curtiss Hawk 75 single-engined fighter. At 10.00, Vichy French ships trying to leave the port received warning shots from Australia. As these ships returned to port, Vichy French-controlled coastal batteries opened fire on Australia. Their guns, which had a range of 8.7 miles (14 km), were 240-mm (9.45-in) modèle 1902 weapons which had come from Vergniaud, a French semi-dreadnought battleship that had been scrapped in the 1920s. An engagement between the Allied fleet and the batteries continued for several hours. In the afternoon Australia intercepted and engaged the Vichy French destroyer L’Audacieux, setting her on fire and causing her to be beached.

Also in the afternoon, an attempt was made to set Free French troops ashore on a beach at Rufisque, to the south-east of Dakar. However, Vichy French reconnaissance aircraft spotted the attempted landing and the attack failed as a result of fog and heavy fire from strongpoints defending the beach. de Gaulle declared he did not want to 'shed the blood of Frenchmen for Frenchmen', and called off the assault.

During the next two days, the Allied fleet continued to attack the coastal defences and the Vichy French forces maintained their efforts to defend them. At first light on 24 September, six Blackburn Skua single-engined warplanes set out to bomb Richelieu, but managed to inflict only minimal damage. Six Swordfish warplanes also attacked the coastal guns, but their attack also caused only limited damage. Another six Swordfish aircraft were launched out to bomb Richelieu. One of these aircraft was hit by anti-aircraft fire and went down in flames, and the remaining aircraft then came under attack from three or four Curtiss Hawk single-engined fighters and a dogfight ensued, in which two or three Swordfish machines were shot down. In total, therefore, four of the nine Swordfish aircrew were killed on the attack on Richelieu. Later in the afternoon nine Swordfish and three Skua warplanes set out on another attack on the Vichy French ships, with two more Swordfish machines lost to anti-aircraft fire. Richelieu's gunners claimed to have shot down three of the British aircraft. Throughout the day, Hawk fighters attacked British aircraft every time they attempted to carry out reconnaissance or attack Vicht French positions.

Eventually, Richelieu was hit by two 15-in (381-mm) shells from Barham. On the second day of action, guns nos 7 and 8, in Richelieu's turret no. 2, failed on their first rounds. The following day, the crews were switched and main turret no. 1 was used. Propellant charges, reconditioned from charges left by the battleship Strasbourg in Dakar during the winter of 1939/40, were used but these gave a significant reduction in range and caused fire-control problems. Over the two days in which Richelieu used her 380-mm (14.96-in) main guns, these fired a total of 24 rounds: among them there seemed to be one near miss on Barham, based on Richelieu's operation journal and British maintenance archives.

During these engagements, a pair of Vichy French submarines, Persée and Ajax, were sunk, and the destroyer L’Audacieux was damaged.

The Allied fleet also suffered damage: Resolution was torpedoed by the submarine Bévéziers, and Barham was hit by two shells from the coastal defence batteries which had been manned by crew from the no 1 main turret of Richelieu. Barham also took blast damage on her starboard lower bulge from a 380-mm (14.96-in) round fired by Richelieu that fell short. The structure was forced inward for 7 ft (2.13 m), causing minor flooding. The heavy cruisers Australia and Cumberland were also damaged. On the final day of action several more dogfights occurred over the skies of Dakar, with the French Hawk fighters generally outgunning the British Swordfish and Skua aircraft.

In overall terms, the 'Battle of Dakar' did not go well for the Allies. The Vichy French forces did not back down. Resolution was so heavily damaged she had to be towed to Cape Town. In most of this conflict, bombers of the Vichy French air force, based in North Africa, bombed the British base at Gibraltar: on 24 September about 50 aircraft dropped 150 bombs while on 25 September about 100 aircraft dropped 300 bombs on the harbour and dockyards. Most of the bombs missed. Some damage was caused, and a few civilians were killed. The raid on 25 September also caused the sinking of the British armed trawler Stella Sirius.

Finally, the Allies withdrew, leaving Dakar and French West Africa in Vichy French hands. The effects of the Allied failure were mostly political. de Gaulle had believed that he would be able to persuade the Vichy French at Dakar to change sides, but this did not happen, which was a result that damaged his standing among the Allies. Even his success in the 'Battle of Gabon' two months later did not wholly repair this damage. de Gaulle would have to content himself with the much less important and economically developed French Equatorial Africa as the main Free French territory for the time being.