World War II: To stop ships from falling into German hands the French fleet of the Atlantic based at Mers El Kébir, is bombarded by the British fleet, coming from Gibraltar, causing the loss of three battleships: Dunkerque, Provence and French battleship Bretagne. 1,200 sailors perish.

The Attack on Mers-el-Kbir (Battle of Mers-el-Kbir) on 3 July 1940, during the Second World War, was a British naval attack on French Navy ships at the naval base at Mers El Kbir, near Oran, on the coast of French Algeria. 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 British bombardment of the base killed 1,297 French servicemen, sank a battleship and damaged five other ships, for a British loss of five aircraft shot down and two crewmen killed.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. Of particular significance to the British were the five battleships of the Bretagne and Richelieu classes and the two fast battleships of the Dunkerque class, the second largest force of capital ships in Europe after the Royal Navy. The British War Cabinet feared that the ships would fall into Axis hands. Admiral Franois Darlan, commander of the French Navy, assured the British, even after the French armistices with Germany and Italy, that the fleet would remain under French control but Winston Churchill and the War Cabinet judged that the risk was too great. Darlan repeatedly refused British requests to place the fleet in British custody or move it to the French West Indies out of German reach.

The British attack was condemned in France and resentment festered for years over what was considered betrayal by a former ally. The French thought that their assurances were honourable and should have been sufficient. Marshal Philippe Ptain, who was appointed the prime minister of France on 16 June, severed diplomatic relations with the United Kingdom on 8 July. The next day, deputies of the National Assembly met at Vichy and voted to revise the constitution, ending the French Third Republic. Ptain was installed with full powers as leader of the new French State.

French aircraft retaliated by bombing Gibraltar and French ships exchanged fire several times with British ships, before a tacit truce was observed in the western Mediterranean. On 27 November 1942, after the beginning of Operation Torch, the Allied invasion of French North Africa, the French Navy foiled Case Anton, a German and Italian operation to capture its ships at Toulon, by scuttling them. In 1997, Martin Thomas wrote that the British attack at Mers-el Kbir remains controversial but that other historians have written that it demonstrated to the world that Britain would fight on.

Mers El Kébir (Arabic: المرسى الكبير, romanized: al-Marsā al-Kabīr, lit. 'The Great Harbor' pronunciation) is a port on the Mediterranean Sea, near Oran in Oran Province, northwest Algeria. It is famous for the attack on the French fleet in 1940, in the Second World War.