On the 17th September 1940, Adolf Hitler, Fuhrer of the Third German Reich, held a private meeting with Luftwaffe commander Hermann Göring and Field Marshall Gerd von Runstedt. Just two months after his triumphant entry into Paris, the news was not good; Operation Sealion – his planned invasion of Britain, had to be cancelled. The dogged British defence that lead to this decision had earned Churchill’s memorable phrase that “this was our finest hour.”
At the start of 1940, the tactical situation had looked very similar to how it had in 1914. Facing Germany’s armies were the British – who had a small but well-trained expeditionary force on the continent, and the French, whose military – on paper at least – was large and well-equipped. As soon as the “Blitzkrieg” invasion of France and the low countries began in May however, the similarities between the two World Wars ended. Where von Moltke’s troops had been stopped von Runstedt’s tanks rolled on remorselessly, carving through British and French defences and forcing the demoralised British survivors onto the northern beaches, hoping for an escape route. For Hitler it had been an astounding success, even more complete, swift and impressive than the famous German victory of 1871 had been. France was utterly crushed, occupied and vanquished, and now only Britain remained. Though hundreds of thousands of Allied troops had been evacuated from the beaches of Dunkirk, much of their equipment, tanks and morale had been left behind, and Hitler was now the undisputed master of Europe. The only obstacle that remained was the same one that had thwarted Julius Caesar two thousand years earlier – the English Channel. Defeating the British armies on the continent had proved achievable, even easy, but overcoming the Royal Navy and landing a strong force across the channel would require far more careful planning.
Preparations for Sealion began on the 30th June, once the French had been forced to sign an armistice in the same railway carriage where the German High Command had been forced to surrender in 1918. Hitler’s real wish was that Britain would see its hopeless position and come to terms. An alliance with the British Empire – which he respected and saw as a model for his own planned empire in the east – had always been a cornerstone of his foreign policy aims, and now, just as he had been before the start of the war, he was perplexed by British stubbornness in resisting even when it was not in their direct interests. Once it became clear that Churchill’s government had no intention of contemplating surrender, attack remained the only option. The early plans concluded that four conditions had to be met for an invasion to have any chance of success:
- The Lutfwaffe would have to achieve almost total air superiority. This had been a major part of the success of the invasion of France, and was vital in a cross-channel attack. Hitler’s most optimistic hope was that air superiority and the bombing of British cities would encourage surrender without the need for a full invasion
- The English Channel had to be swept of mines at all crossing points, and the straights of Dover had to be completely blocked by German mines
- The coastal zone between Calais and Dover had to be covered and dominated by heavy artillery
- The Royal Navy had to be sufficiently damaged and tied down by German and Italian ships in the Mediterranean and the North Sea for it to be unable to resist an invasion by sea.
The first condition for the launch of Sealion was the most important, and therefore plans for what became known as the Battle of Britain were advanced quickly. Initially, the Germans targeted strategic naval and RAF targets to bring the British military to its knees, but after the 13th August the emphasis switched to bombing the cities, particularly London, in a bid to scare the British into surrender. Many historians agree that this was a serious error, as the RAF had been suffering from the onslaught, but the population of the cities proved more than able to withstand the pressure of the bombardment, just as German civilians would later in the war. The combat in the air over Britain’s countryside, which took place throughout the glorious summer of 1940, was brutal for both sides, but the RAF gradually exerted their superiority. Though the battle was far from over in early September, it was already clear that Hitler’s dream of air superiority was a long way from being realised.
That left the war at sea, which was, if anything, even more crucial for Sealion’s success. In this respect Hitler had to overcome serious problems from the outset of the war. The British Empire, unthinkable though it might be today, was still a formidable naval power in 1939, and needed to be in order to maintain its geographically scattered empire. The German Kreigsmarine was significantly smaller, and its most powerful arm – U-Boat submarines, was of little use in supporting a cross-channel invasion. Furthermore, despite the success of the Norwegian campaign earlier in 1940 against the British on land, it had been very costly in terms of naval losses, and Mussolini’s fleet had also taken a mauling in the war’s opening exchanges in the Mediterranean. The best opportunity for evening the odds at sea was presented by the navy of the defeated French, which was large, modern and well-equipped. Churchill and his High Command knew this, and in early July he conducted one of his most ruthless but important operations, the attack on the French fleet anchored at Mers-el-Kébir in Algeria, in order to prevent it falling into German hands. The operation was a complete success and the fleet was virtually eliminated, and though the terrible effect on relations with Britain’s former ally was predictable, Hitler’s last chance to take on the Royal Navy was gone. After this, most of the Fuhrer’s top commanders were outspoken in their belief that any attempted invasion was too risky to be contemplated. If the Nazi regime was seen to fail on the international stage, then the fear and bargaining power that its victories in France had bought would be lost.
As a result of all this, Hitler eventually had to concede by mid-September that Sealion would not work. Though he used the term “postponed” rather than “cancelled” to soften the blow, such an opportunity would never present itself again. The received wisdom about the war is often that the Fuhrer committed a terrible tactical blow by attacking the Soviet Union in the spring of 1941 before finishing off Britain, but in truth, he had little choice. Churchill’s government had no desire to seek terms, and the oldest and most terrible enemy of National Socialism seemed, ironically, to be an easier target by the end of 1940. The Nazi dreams of restoring Edward VIII to the throne and creating a huge headquarters at Blenheim Palace would have to wait for a victory against the Soviets that never came. It could be said therefore, that the cancellation of Sealion was the true turning point of World War 2.