Britain’s devastating attack on the naval fleet of Vichy France docked at Mers el Kébir near Oran in French Algeria on July 3rd, 1940 was part of an audacious plan codenamed Operation Catapult. It ensured that the British maintained their traditional naval supremacy and the Germans, having defeated the French on land, didn’t take over a relevant part of the fourth’s biggest navy at the time: two modern battlecruisers, two older battleships, six destroyers and a seaplane carrier, which after the Battle of Dunkirk had escaped from Brest on the Atlantic coast to North Africa, though remained loyal to the new government in Paris.
The crews of two battleships, three submarines and eight destroyers under French command, which had chosen Plymouth and Portsmouth, had been transferred to internment camps on the Isle of Man in the Irish Sea and near Liverpool.
London had announced that it would agree to the surrender of its former ally on June 25th only under the condition that all French ships ended up in British harbors. The British wanted to avoid at all cost that the balance of sea power tilted decidedly in favor of the Axis powers, not only in the western Mediterranean.
They were unaware of an instruction by Admiral François Darlan, Chief of Staff of the Navy, who as early as June 20th had instructed the captains of the warships based in French African ports, including Dakar in Senegal, not to surrender any vessel intact to the victorious Germans. On June 24th, he had even ordered to make preparations to scuttle all of them to avoid being captured.
In consequence, the British on June 28th created Force H, consisting of one battlecruiser, two battleships, one carrier and eleven destroyers to assemble at Gibraltar under the command of Vice-Admiral James Somerville to make sure the envisioned transfer, surrender or destruction.
When on July 3rd Force H arrived at Mers el Kébir, the commander of the French Raiding Force, Admiral Marcel-Bruno Gensoul, was given four choices: join the British and continue to fight the Germans, be escorted to the French West Indies or to a British port, have the ships disarmed under British supervision or sink them right there.
Although Somerville after tense talks that only lead to the assurance that the French wouldn’t start any action themselves made clear his will to use force if Admiral Gensoul refused to accept any of these options, he still hesitated, but obtained confirmation of his superiors’ “firm intention”.
After the British had mined the entrance to the harbor, and Darlan was informed that the fleet would be destroyed within six hours, he ordered naval reinforcements to assist Gensoul. In the light of facing a growing number of opponents, the Royal Navy shortly before 6:00 PM opened fire for thirteen minutes from the open water on the French that were in a confined space with devastating effects.
One modern battlecruiser sank, and the two older battleships as well as four destroyers and the seaplane carrier were damaged to different extents. The other battlecruiser and four destroyers managed to get to Toulon in southern France. Although Force H returned to its base, on July 6th British planes finished off a battleship that supposedly had sustained only minor damage toe days earlier, putting it out of action for about a year.
The killing of almost 1,300 men and the wounding of another 350 who had just helped to evacuate British troops from Dunkirk fueled strong anti-British sentiment in France. Seen by many as another sign of English treachery and ruthlessness, it might have encouraged more French people to collaborate with the Germans. On July 4th, 1940 Vichy France severed diplomatic relations with Great Britain.
That was also the day that Winston Churchill, Prime Minister since May 10th, 1940, for the first time since received a unanimous standing ovation in parliament. Mistrustful of French promises that the navy would be used only for supervision and minesweeping and wary of German might, the British decided to immobilize most of it. In any case, it showed Britain’s firm determination to fight Germany by all available means.
P.D.: The French navy ships under Admiral René-Émile Godfroy docked in the Egyptian port of Alexandria were offered the same terms on the same day. Godfroy opted to keep them there until May 1943.