I'd also like to point out that the RAF was never really close to defeat. At the point where Germany thought they had them and switched to London, believing that they had the RAF down to the last hundred operational planes, the RAF actually had more planes than ever before.
Before the Battle Of Britain, Germany estimated that England can produce no more than 180-300 fighter planes per month. It was a gross underestimation. By October 1940, Britain had actually produced some 2000 new Spitfires and Hurricanes, or more than double their losses. The number of operational RAF fighters was actually going UP and fast.
By contrast, Germany produced about half as many new planes in that period, and the difference between new planes and losses was much smaller. I.e., the Luftwaffe was growing its number of planes a LOT slower than the RAF was growing theirs.
Additionally, Germany was losing its experienced pilots faster. Just because a German pilot bailing out over England was out of the fight, while a British one could be back in another plane right away.
But let's also look at what supporting an invasion would have actually meant.
Germany would have needed to:
- have enough sea-worthy transports in the first place, which they didn't
- have the Luftwaffe protect not just the troop transports, but also the ferrying over a stream of supplies for them
- AT THE SAME TIME, the Luftwaffe was supposed to act as flying artillery for the invading troops, because they didn't have enough transport capacity for a lot of tanks and artillery for those initial troops too
- have naval shipyard capacity to replace the transports they'd be losing fast. Which if you look at their naval production otherwise, it was nowhere near enough for that kind of massive effort
... all while the RAF was growing its numbers superiority very fast.
Additionally, there's this myth of the German elite troops, being awesome against huge odds. Actually, they weren't. They really only did well when they had overwhelming numbers concentrated in one point, against defenders that could be thus overwhelmed. Also the whole Bewegungskrieg concept (literally "movement war"; the Germans didn't actually use the term Blitzkrieg) needed space for maneuver. An invading army in Britain would at no point have either.
And encircling the Brits after an invasion would have been a problem too.
But let's look deeper at how the whole Bewegungskrieg worked. Once you actieved that concentrated punch you'd break through and try one of the following:
- encircle some of the troops you bypassed
- keep going and cause chaos, while they chase you; only Rommel really managed to pull this stunt
- occupy some position and let them attack you, until the rest of the army links with you
Mostly the latter was the big evolution, so to speak. But that doesn't work when you also have to keep a supply corridor to the shore. If you just punch through and move on (which wouldn't be easy in the first place with not enough tanks ferried over), the Brits close the beachhead and now YOU are the one encircled.
I'm not saying an invasion would generally be impossible, but Sealion? Even if Germany found a thousand seaworthy transports somewhere, it just wouldn't work. Just too many problems, really.
