Force H was a British naval formation during the Second World War. It was formed in late-June 1940, to replace French naval power in the western Mediterranean removed by the French armistice with Nazi Germany. The force occupied an odd place within the naval chain of command. Normal British practice was to have naval stations and fleets around the world, whose commanders reported to the First Sea Lord via a flag officer. Force H was based at Gibraltar but there was already a flag officer at the base, Flag Officer Commanding, North Atlantic. The commanding officer of Force H did not report to this Flag Officer but directly to the First Sea Lord, Admiral of the Fleet Sir Dudley Pound.

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.