It is interesting that the Luftwaffe only got a few destroyers at Dunkirk. It begs the question, how many ships would the RAF got in a cross channel invasion by Germans, & how many ships would Germans need to get across for it to be a success?
For that matter, how sophisticated was aerial ship bombing in 1940? skip bombing had not been developed yet. The techniques for sinking ships from the air went through much upgrade in subsequent yrs.
How many German battleships and battle cruisers were running through the withdrawal forces ripping it to shreds? There would have been plenty of RN capital ships, cruisers and destroyers in a target-rich environment.
Germany had no amphibious warfare doctrine. Didn't get to practice it in Spain, didn't plan on any invasions, didn't figure at all in the goals of the Third Reich. They had no specialized vessels, no Higgins boats, no LSTs, no Mulberry docks, no sophisticated fuel logistics (no pipeline on the channel bed to the coast) to keep the army moving once ashore, no means to get those 50 panzers off a transport ship and onto the beach without controlling a port, no naval superiority (not even in U-boats at this time), would have been opposed to some degree in the air (enough to disrupt Stukas attacking the RN certainly) and would be facing the full, unoccupied commonwealth forces in Britain.
There is a reason why the allies waited until 1944, took full advantage of massive numbers of specialized US produced support vessels, massive naval bombardment, a diluted german force with much on the Eastern front, hard earned amphibious doctrine from the Pacific and overwhelming air superiority. Nobody could have pulled of a similar invasion in 1939 because the scope of the undertaking was too massive compared to the defense required to resist. The amount of mental gymnastics required to make this successful borders on the realm of science fiction (not alternative history). The channel was a *****. Logistics is a *****. Pile up enough dirt to fill in the English Channel and maybe it becomes a different story
Charon