The last major naval conflict between British and French forces didn’t involve point-blank broadsides from Napoleonic-era sailing ships, but instead occurred 70 years ago today, during World War II.

The attack on Mers-el-Kébir, part of Britain’s Operation Catapult, was a one-sided engagement off the coast of French Algeria on July 3, 1940, in which a Royal Navy task force attacked and destroyed much of the French fleet, killing 1,297.

France and Britain were not at war, but France had recently signed an armistice with Nazi Germany and Britain feared the French fleet would end up as a part of the German Navy.

Although French Admiral François Darlan had assured Winston Churchill the fleet would not fall into German hands, the British acted upon the assumption that Darlan’s promises were insufficient guarantees.

The attack was brutal in its ferocity and efficiency.

A British force consisting of the battlecruiser HMS Hood, battleships HMS Valiant and Resolution, and the aircraft carrier HMS Ark Royal, plus an escort of cruisers and destroyers, gave the French fleet, anchored in a narrow harbor, an utlimatum to surrender or be taken.

The French did not expect an attack and were not fully prepared for battle. The main armament of two of their key ships, the Dunkerque and Strasbourg, could not immediately be brought to bear.

The British opened fire a little before 5 p.m. The French eventually mounted an ineffectual reply.

The third salvo from the British force and the first to hit resulted in a magazine explosion aboard Bretagne, which killed nearly 1,000 of her crew.

After some thirty salvos, the French ships stopped firing. Provence, Dunkerque and the destroyer Mogador were damaged and run aground by their crews.

The Strasbourg managed to escape with five destroyers and eventually reached the French port of Toulon on the next day.

Besides nearly 1,300 French sailors killed, another 350 or so were wounded. The British lost just six dead. Not surprisingly, relations between Britain and France were severely strained.

British Admiral Somerville was not enthusiastic about the action, saying that it was “… the biggest political blunder of modern times and will rouse the whole world against us … we all feel thoroughly ashamed …”

Indeed, the attack on the French vessels at port sowed anger amongst the French towards the British and increased tension between Churchill and the leader of the Free French Forces, Charles de Gaulle.

But the action demonstrated Britain’s resolve to continue the war alone, and rallied the British Conservative Party around Churchill. Churchill later declared the action meant that for “high government circles in the United States … there was no more talk of Britain giving in.”