Just to make some points:
Swimming Tanks - all very well for crossing a river or small lake, no use at all for the English Channel (famous for it’s sudden storms), a swimming tank would be useless for the invasion.
(by the way Gen Sandworm - the DD tanks were invented by the Brits - we showed you how to make them (and many other special tanks, which you weren’t interested in and could have saved you casualties at D-Day))
Bombing Airfields - proved to be very hit and miss during the whole Battle of Britain. The British aircraft were very well dispersed (spread out) around the airfields and were protected by revetments (big walls of earth or concrete), so only a direct hit could damage them. The medium bombers were not accurate enough to that and the stuka was too vunerable to be used.
Germany invading USSR - they could have won IF they hadn’t been fighting on two fronts and IF Hitler had let his Generals run the war. Splitting and weakening their forces by being forced to defend France meant that the Whermacht just weren’t strong enough to face the Red Army.
Naval invasion of Britain - impossible for Germany in 1940. They only had one capital ship available in 1940 (Graf Spee had been sunk, Scharnorst, Tirpitz and Bismark still being built). The Royal Navy would have destroyed an invasion fleet in a few hours - Churchill would have risked losing most of the fleet to destroy the German fleet, knowing full well we could (if required) pull our naval assets from the Med, Far East etc back to form a new Home Fleet.
Dunkirk - had the major part of the BEF been captured, we would have had severe problems defending ourselves, however the Germans would still have had to cross the Channel, and there would have been more chance of Churchill sacrificing the Home Fleet if he knew there was so few ground forces to face an invasion.
RAF strength - The strength of the RAF was actually improving when the Germans switched to bombing civillians. The problems for the RAF were training pilots quick enough - fighter production was actually faster than Germany’s (I’ll post the exact numbers tomorrow if anyone wants them).
Destroying radar - the Luftwaffe tried many times to bomb the radar towers, because of their spindly towers, they allowed bomb blast to disperse rather than being damaged by it, so they were very resistant to bombing raids.
Providing air support in France - we supplied as much as we dared, sending anymore squadrons to France would have left us unable to defend ourselves.
Britain pre-war production - we were building our forces up as quickly as we could. The Wall Street crash and Depression had hit us hard. It’s worth remembering that we were the only 100% Mechanised Army in 1939 - even Germany still used a large number of horses. It was our tactics (remember most armies prepare to fight their last war rather than their next one. Germans used Blitzkreig because they had lost their last war and wanted to avoid a long stalemate that would allow Britain to build her strength up against them again as they had in 1914/15/16.
Appeasement - as much as I hate it, it was the most sensible way we could have gone at the time. We weren’t strong enough to provoke war in 1938 over Czechoslovakia and needed the breathing space that Munich gave us to build up.
British Commonwealth - still exists today, but I’ll find the topic already existing for that arguement.
Sorry it’s such a long post, I didn’t want to miss anything out.