[3][a] The attack was the main part of Operation Catapult, a British plan to neutralise or destroy French ships to prevent them from falling into German hands after the Allied defeat in the Battle of France.

The attack by air and sea was conducted by the Royal Navy, after France had signed armistices with Germany and Italy, coming into effect on 25 June.

Marshal Philippe Pétain, who was appointed the Prime Minister of France on 16 June, severed diplomatic relations with the United Kingdom on 8 July.

In 1997, Martin Thomas wrote that the British attack at Mers-el Kébir remains controversial but that other historians have written that it demonstrated to the world that Britain would fight on.

Although Churchill feared the fleet would be used by the Axis, the need to man, maintain and arm the French ships with items that were incompatible with German and Italian equipments made this unlikely.

[13] The Kriegsmarine and Benito Mussolini made overtures but Adolf Hitler feared that an attempted take-over would provoke the French fleet into defecting to the British.

[16] Admiral James Somerville, commander of Force H, based in Gibraltar, was ordered to deliver an ultimatum to the French, the terms of which were contrary to the German–French armistice.

[14][b] Somerville passed the duty of presenting the ultimatum to a French speaker, Captain Cedric Holland, commander of the carrier HMS Ark Royal.

[14] Removing the fleet to US waters had formed part of the orders given by Darlan to Gensoul in the event that a foreign power should attempt to seize his ships.

On 3 July, before negotiations were formally terminated, six British Fairey Swordfish planes escorted by three Blackburn Skuas from Ark Royal dropped five magnetic mines in the harbour exit.

The Préfet Maritime at Toulon ordered two submarine groups, A, consisting of L'Espoir, Le Conquérant and Archimède and B, comprising Iris, Vénus, Sultane, Sirène, Pallas and Cérès to assist the French at Oran by attacking British ships, Hood in particular.

[25] Provence began its reply within 90 seconds of the British opening fire but the main armament of Dunkerque and Strasbourg was forward of the superstructure and could not immediately be brought to bear because they were tied up at the mole, with their sterns facing the sea.

[16] The third British salvo hit Bretagne and detonated a magazine, the ship sinking with 977 of her crew at 6:09 p.m. After thirty salvoes, the French ships ceased fire; Force H altered course to avoid return fire from the French coastal forts but Provence was badly damaged by several hits, Dunkerque was hit by three shells, severely damaged and run aground to avoid sinking, the destroyer Mogador lost its stern and two other destroyers were damaged; their crews running them aground to prevent them from sinking.

[26] Strasbourg, three destroyers and one gunboat managed to avoid the mines and escape from the port under attack from a flight of Swordfish bombers from Ark Royal.

Rigault de Genouilly, en route to Oran, met Force H at 7:33 p.m. and steamed towards Hood, only to come under fire from the light cruisers Arethusa and Enterprise at 12,000 and 18,000 yd (5.9 and 8.9 nmi; 6.8 and 10.2 mi; 11 and 16 km) respectively.

[28] The French Air Force (Armée de l'Air) made reprisal raids on Gibraltar, including a small night attack on 5 July, when many bombs landed in the sea.

[31] The British believed that the damage inflicted on Dunkerque and Provence was not serious and on the morning of 8 July raided Mers-el-Kébir again in Operation Lever, with Swordfish aircraft from Ark Royal.

The British action showed the world that defeat in France had not reduced the determination of the government to fight on and ambassadors in Mediterranean countries reported favourable reactions.

[35] The French ships in Alexandria under the command of Admiral René-Emile Godfroy, including the old battleship Lorraine and four cruisers, were blockaded by the British on 3 July and offered the same terms as at Mers-el-Kébir.

After delicate negotiations, conducted on the part of the British by Admiral Andrew Cunningham, Godfroy agreed on 7 July to disarm his fleet and stay in port until the end of the war.

[38] Jean Lacouture, in a biography of De Gaulle, blamed the tragedy mainly on miscommunication; if Darlan had been in contact on the day or if Somerville had possessed a more diplomatic character, a deal might have been done.

[40] In 2010, Colin Smith wrote that the attack was the first big triumph of Churchill's premiership and that they had been received favourably by the governments of the US, Turkey, Greece and Brazil, with condemnation from Spain and Switzerland.

Count Galeazzo Ciano, the Italian foreign minister, made a diary entry that the Royal Navy retained the "ruthlessness of the captains and pirates of the C16th".

Melton wrote that the attack was unnecessary, because the French Navy had pledged and planned to scuttle its ships as a matter of honour rather than see them fall into German or Italian hands.

Melton suggested that Churchill's anger at France for its capitulation to the Axis and his "obsession" with seizing or sinking the four modern French battleships (Jean Bart, Richelieu, Dunkerque, and Strasbourg) was largely responsible for the attack.

[49] On 19 November 1942, the Germans tried to capture the French fleet based at Toulon, against the armistice terms, as part of Case Anton, the military occupation of Vichy France by Germany.

All ships of any military value were scuttled by the French before the arrival of German troops, notably Dunkerque, Strasbourg and seven (four heavy and three light) modern cruisers.

In these circumstances, His Majesty's Government have instructed me to demand that the French Fleet now at Mers el Kebir and Oran shall act in accordance with one of the following alternatives; (a) Sail with us and continue the fight until victory against the Germans.