The Destruction of the French Fleet at Mers-el-Kebir, French North Africa (now Algeria), by the British Royal Navy took place on July 3, 1940.

In 1940, during World War II, following the surrender of France to the advancing forces of Nazi Germany, the British were unable to discover whether the terms of the surrender would allow the French fleet to be used against Britain. Such a shift in the balance of power at sea would have seriously threatened Britain's ability to keep her supply lines open, and jeopardised her survival. Winston Churchill therefore personally ordered that the French navy should either fight alongside the Royal Navy or be neutralised in some way, preventing it from falling into German hands. To prevent this, they launched Operation Catapult.

The French fleet was widely dispersed at this time. Some were in port in France; others had escaped from France to British controlled ports, mainly in Britain itself or Alexandria in Egypt. Those ships in Britain were simply boarded. Many went on to be used by the Free French forces, and some sailors joined the Free French. Others were repatriated to France.

The most powerful concentration of French warships at the time was the flotilla located at the port of Mers-el-Kebir in French Algeria. This consisted of the old battleships Provence and Bretagne, the modern battleships Dunkerque and Strasbourg, the aviation transport Commandante Teste and 6 destroyers, all under the command of Admiral Marcel-Bruno Gensoul. The British Admiral James Somerville of Force H, based in Gibraltar, was ordered to deliver an ultimatum to the French, stating:

"It is impossible for us, your comrades up to now, to allow your fine ships to fall into the power of the German or Italian enemy. We are determined to fight on until the end, and if we win, as we think we shall, we shall never forget that France was our Ally, that our interests are the same as hers, and that our common enemy is Germany. Should we conquer we solemnly declare that we shall restore the greatness and territory of France. For this purpose we must make sure that the best ships of the French Navy are not used against us by the common foe. 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 and Italians.

(b) Sail with reduced crews under our control to a British port. The reduced crews would be repatriated at the earliest moment.

If either of these courses is adopted by you we will restore your ships to France at the conclusion of the war or pay full compensation if they are damaged meanwhile.

(c) Alternatively if you feel bound to stipulate that your ships should not be used against the Germans or Italians unless these break the Armistice, then sail them with us with reduced crews to some French port in the West Indies — Martinique for instance — where they can be demilitarised to our satisfaction, or perhaps be entrusted to the United States and remain safe until the end of the war, the crews being repatriated.

If you refuse these fair offers, I must with profound regret, require you to sink your ships within 6 hours.

Finally, failing the above, I have the orders from His Majesty's Government to use whatever force may be necessary to prevent your ships from falling into German or Italian hands."

Admiral Gensoul refused, and both fleets prepared for battle. In the ensuing action on July 3, 1940, Bretagne was sunk, while Provence and Dunkerque were badly damaged, with over 2,000 French sailors killed. Strasbourg meanwhile was able to escape and return to the French port of Toulon. The action severely strained relations between Britain and France for some time, and gave the Germans a propaganda coup.

However, the action was very influential amongst the leadership of the United States, which was gradually preparing public opinion for escalating involvement in the war. Following the rapid success of the German military, there was considerable speculation that the United Kingdom would soon fall. There seemed to be a great risk that the Royal Navy would fall into German hands, including any material provided to the British by the USA. Martin Gilbert in his biography of Churchill wrote "Within a few days "Oran" had become a symbol of British ruthlessness and determination".

Churchill noted to a colleague that the French at Oran finally fought "with all their vigour for the first time since the war broke out".