Curious thought, but might a LONGER battle of France actually help Sealion? 1) more English Resources used up defending Paris or Rouen. Of course, there will be more German casualties too, but overall with Germany being victorious, they will still have more men and guns left in the end. 2) Germany having more time to build up Dunkirk and Calais while the British ports are busy ferrying supplies to Normandie. By the time France is defeated, Germany would have working S-boat and U-boat squadrons in Belgium and the north of France. While still no match for the Royal Navy, they could still deprive the English at least the uncontested rule of the sea. 3) Finding out that Britain will not roll over dead on command, Germany will already have to think at least seriously about landing on the island. Each day the war in France drags on, it will have one more day to plan the invasion and to design and manufacture the hardware needed. Yes we might still see the Germans using seized Dutch river barges, but just as well, they will have their share of purpose-built commando-lighters or even giant sailplanes and more importantly, they will have their share of ferries and packetboats in place to run the supply chain for the second wave once the beaches are secured.