This discussion is going much as I expected.
Let me consolidate this discussion.
Air superiority was a requirement for the invasion. The Luftwaffe did not gain it, but there is the real possibility that they could have in the August-September period if they had persisted in a war of attrition rather than shifting targets to the cities.
Considering the neutering of the combat effectiveness of the Luftwaffe by the higher leadership, it makes you wonder how the battle would have progressed without the interference from up on high - offensive fighter sweeps and attacks on the radar stations are what I mainly have in mind.
In regards to the naval aspect of the invasion: the KM would have the following capital ships
- Bismarck (commisioned 24 August 1940, would take some effort to be combat ready for the proposed invasion in Sept)
- Admiral Hipper
- Prinz Eugen (Commisioned 1 August 1940)
Plus sundry other smaller warships. Hardly overwhelming force, but enough to ensure that the RN would face some significant resistance. .
Against this, they have to fight off the bulk of the Royal Navy, but the RN had no intention of commiting their capital ships to interfere with an invasion. This just leaves the crusiers and destroyers of the RN, so even the older German battleships would significantly out-gun the opposition.
Considering what happened to the Prince of Wales and the Repulse a year later, I wonder of the value of the RN sending big surface combatant ships into the range of the Luftwaffe - if the losses of the RN at Crete are anything to go by, the result wouldn't be favourable to the RN.
The whole point of the barges were to enable the Whermacht to get enough troops ashore that they can capture a major port and start unloading troops through that. If they'd worked well, the Germans wouldn't have needed a port.
The success of Operation Sea Lion depended on three factors:
1. The Luftwaffe maintaining air superiority over south-eastern England prior and during the invasion.
2. Combined efforts of the Luftwaffe and KM limiting the damage that the RN can cause to the invasion flotilla.
3. German ground forces securing sufficent ports to enable reinforcement and resupply of the invasion force.
Now, the original quote that you posted that I took issue of was this:
There is one positive item you can add to that depressing list - a successful Operation Sealion was simply impossible.
None of those three factors were "impossible". They were unlikely to be attained, but none were absolutely unattainable.
There are many examples throughout history of things claimed to be "impossible" when, in fact, they are not. Someone who reads as much history as yourself should not be making that mistake.