Operation Sea Lion
After the German blitzkrieg through Western Europe culminated in France’s surrender in 1940, Hitler assumed that Britain would seek peace terms. When that did not happen, he ordered plans be drawn up for invading Britain, Operation Sea Lion. A prerequisite for success was German air superiority over southern England and the English Channel. Otherwise, between the Royal Navy and the RAF, an invasion force would get mangled at sea, and any survivors who made it to land would end up cutoff on isolated beachheads and quickly defeated.
The need to defeat the RAF as a preliminary to Sea Lion was the driving motive for the Battle of Britain, and during the summer and early fall of 1940, a battle of attrition raged over British skies. The Germans tried their best, and came close on more than one occasion, pushing the RAF to its limit, and past that at times. But Fighter Command kept managing to send up just enough pilots, exhausted and wearied but still game, to contest the issue and savage the attacking Germans.
In the end, the Germans blinked first. Realizing that the aerial supremacy necessary of Sea Lion’s success was unattainable, the Luftwaffe shifted to night time terror bombing, the Blitz, in a bid to break Britain’s national will and cudgel it into suing for peace. Sea Lion was shelved, the invasion of Britain was abandoned, and the Germans began shifting their forces to the east, in preparation for an attack on the Soviet Union the following summer.
However, it is likely that Sea Lion never stood a chance, and Britain was never as vulnerable to invasion in 1940-1941 as is commonly assumed. Whatever the outcome of the aerial Battle of Britain, Britain’s leaders knew early on that the Germans could not successfully invade because they lacked the shipping and landing craft necessary to transport and support an invasion force strong enough to subdue Britain. The main reason the Allies invaded France in 1944, rather than 1943 as American commanders wanted, was the lack of sufficient landing craft. That problem was even worse for the German in 1940-1941. British leaders kept that to themselves, however: the national spirit of defiance and public morale was high in the face of an “expected invasion”, and there was nothing to be gained from tinkering with that and possibly inviting complacency.