The attack on Mers-el-Kébir on 3 July 1940, during the Second World War, was a British naval attack on neutral French Navy ships at the naval base at Mers El Kébir, near Oran, on the coast of French Algeria. The attack was the main part of Operation Catapult, a British plan to neutralise or destroy neutral 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.

The French Navy, informally La Royale, is the maritime arm of the French Armed Forces and one of the four military service branches of France. It is among the largest and most powerful naval forces in the world recognised as being a blue-water navy. The French Navy is capable of operating globally and conducting expeditionary missions, maintaining a significant overseas presence. The French Navy is one of eight naval forces currently operating fixed-wing aircraft carriers, with its flagship Charles de Gaulle being the only nuclear-powered aircraft carrier outside the United States Navy, and one of two non-American vessels to use catapults to launch aircraft.