Interesting. But no one can say for sure because no one did the experiment. A cross channel invasion was very vulnerable to small boats as a defensive force. Ironically in 1944 the Germans proved that during a training exercise that they managed to stumble into. That did them no benefit in June as they were, of course, waiting for the Calais invasion. The English Army fighting a defensive war in 1940 on it’s own turf probably would fight a trench war — which might have worked. It’s a defensive tactic, it works well against Infantry, which still was the primary component of the German Army. And the English knew where the Germans were going to attack. The weather, God’s main joker, would have played a part. Had it occurred it would have been bloody and messy and difficult, and the German Army was already working at the limits of it’s logistics.
And let’s ignore the extensive history of seriously screwed up slap-dash amphibious operations that proves the point of the US Marines. Successful amphibious operations are hard.
What did Adolf want? All wars are political exercises. England had no resources, a bolshy industrial workforce, second rate factories that didn’t use metric, bad food, and was not critical to a continental strategy. It’s only threat was a threat at sea, but not a threat of invading Greater Germania.
The destruction of the RAF was a military goal but mainly a political goal. Stripped of their last defenders the English would see sense, toss out that fool Churchill, and sue for peace. The best German outcome in the Battle of Britain would have been bringing to power a government that would make a peace preserving the Empire and preserving England from invasion. That might have happened. It occurred in the same year the King had vacillated between Churchill and Lord Halifax, who would have made peace, as Prime Minister; Halifax declined and settled the matter. By the end of the Battle of Britain a British population that might have accepted a bad peace was as galvanized as the Finns were against a foreign invasion. They could fight back, even when victory looked to the realistic impossible.
Hitler hated fighting wars where he couldn’t win quickly. Poland was quick. The War with the UK and France was unexpected and deeply surprising. The conquest of France was a gamble — that worked! It was fast. The Balkans and Greece were Fast. Norway had been fast. Later when he turned to the Soviet Union he expected that war to be fast. He said something like “kick in the door and the whole edifice will tumble down.” That was a gamble that he lost. An invasion of England would be fought inch by inch assisted by a civilian population that would not flee but would resist. Hitler didn’t want that. He had had a belly full of that between 1914 and 1918.
When the Battle of Britain failed Adolf let loose the U-boats to starve out England. Maybe that would bring them to their senses and an honorable peace. Which would you rather do? Spend a few dozens, maybe a few hundred u-boat crews to starve England into submission or hundred of thousands of dead and wounded soldiers? Those wounded would be a drain on the economy for 40 years.
Adolf’s calculus might make no sense to us but he didn’t hate the English and he didn’t fear them either. Isolated on their little island they could do him no harm for years. He was right about that. They could be starved out. If the U-Boat arm had started out with 250 U-Boats instead of under a hundred he probably would have been right about that, too. The real threat, the ultimate threat, the ultimate opportunity lay in the East.
The real irony of the Second World War is that the democracies only won, only clawed back what had been “theirs” in 1939 (unfortunately most of Eastern Europe was under one form or another of authoritarian tule), because the two worst human beings alive, Hitler and Stalin, fought to the death of their armies.