VE Day in Piccadilly Circus - but what turned the war? Copyrighted image Credit: Used with permission So you think the Battle of Britain was the defining moment in preventing a German invasion…?

Actually, it’s not as simple as that. Impressive though the defeat of the Luftwaffe was, the truth was that only the Royal Navy would save Britain during a seaborne invasion, and it was unchallenged by the Germans – until the fall of France and the capture of the entire French Navy. With that fleet, Germany could have destroyed the real defender of Britain, the Royal Navy. So the Royal Navy destroyed the French Fleet first, at Mers-El-Kebir. That place name that has disappeared from history but it was the venue for an event which did as much to save Britain as “the few”. The Battle of Britain is a plucky story and one the American public loved – but it wasn’t the only show in town.

The popular view of the Battle of Britain is that it was a turning point in the Second World War and a decisive battle. Had it been lost by Fighter Command, Britain would have been exposed to invasion, and defeat would have been likely. This view, while exaggerated, isn't entirely irrelevant. The battle dramatised an important moment as the British Empire fought alone against Germany and Italy for a few months. It was also important as the first British aerial victory of the war.

But even if it had been lost, invasion was never a realistic possibility. The German Navy had three capital ships in the summer of 1940: the Royal Navy had twelve. In lighter ships, the ratio was even more crushing, approaching 10:1 in the crucial area of destroyers. Italian belligerence evened the balance somewhat, but did not alter it. In order to get their delicate invasion barges to Britain, and to supply their force long enough just to take London, the Germans would have needed to command the Channel. They could not do this, and they would not have been able to do this even had they won the Battle of Britain – evidence from the Norway and Crete campaigns demonstrates that they could not sink ships from the air fast enough.

In June 1940, the only fleet large enough to have a chance  of threatening the Royal Navy was that of France. France's surrender posed the possibility that this might fall into German hands, and Churchill acted ruthlessly to prevent that happening, ordering his admirals to neutralise the French ships at all costs and at great speed. One admiral, in Gibraltar, protested at these orders – he was later sacked. Another, in Alexandria, ignored them and successfully spent several days negotiating a French disarmament. In Oran, North Africa, a third, carried the orders out to the letter, and this, combined with the inflexibility of his French opposite number, led to the attack by the Royal Navy on the French base of Mers-el-Kebir on the 3rd of July 1940. Three French battleships were put out of action and over a thousand sailors died on them.

This was the decisive battle of 1940 that saved Britain from the possibility of invasion. With the Navy safe, the Battle of Britain could have been lost and invasion would probably still not have been possible. In fact it was won, and for obvious reasons became the symbol of that period. Meanwhile, Mers-el-Kebir was forgotten.

First broadcast: Monday 16 May 2005 on BBC Radio 4