I often think at this time of year about what would have happened if Hitler had ordered the invasion of Britain in the summer of 1940. A reason for my interest is that I live in Canterbury in east Kent; the coast where the German invasion would have taken place between Folkestone and Newhaven is half an hour’s drive to the south.
I have often stood on top of the Western and Eastern Heights at Dover looking at the French coast 20 miles away, which is so clearly visible and makes the Channel feel more like a broad river rather than a narrow sea.
Another reason for thinking about the non-invasion of 1940 is that Britain was lucky then and I wonder if its luck as a country has deserted it, as one grossly inadequate government succeeds another.
In the event, Hitler decided to postpone and then abandon the invasion. But he said later in the war to his intimates that he believed that his biggest mistake was allowing the German navy to dissuade him from giving the order for the attack.
Many argue that the German barges could not have crossed the Channel because the RAF won the Battle of Britain and denied the Luftwaffe air superiority. This may be true of south east England as a whole, but the Luftwaffe could certainly have gained superiority over coastal east Kent, which was all it needed for an invasion. The Royal Navy could not be permanently stationed in the Channel to stop the invaders without sustaining catastrophic losses from air attack.
Once a German seaborne invasion force or paratroopers had seized a few airfields, they could have brought in reinforcements by air. They were able to do this during the battle for Crete in 1941, despite the Royal Navy having control of the sea.
An understanding of how desperate the situation really was may explain why Churchill and his senior generals made elaborate plans to use poison gas if the Germans got ashore. I wrote a long piece about this some years ago.