The premise was the US & UK v USSR & Germany in 1940/1941. Okay, so Germany does not have French ports......only can get out through from Baltic ports.......that is a blockade which is easily handled by the resources of the Royal Navy. The Kriegsmarine had only 56 U-boats at the outbreak of the war. The Soviets had about the same. The Royal Navy had 184 destroyers. The US Navy had 171 destroyers. Never mind cruisers, battleships and, oh yeah, aircraft carriers. Since there was no war in the Pacific, the US can put most of its force against the Germans.....with some of it taking care of Vladivostok. German amphibous design was rather poor at best...as they proved. Remember, the Germans never tried to cross the Channel when they had local air superiority...that is because they never gained parity, let alone superiority, at sea. So, Germany & USSR would be preeminent on the continent as greta land powers. The US & UK would have held them there. The US & UK had the concept of strategic air forces and could start and maintain a bombing campaign against German shipyards to keep it that way (remember...no France) As for all of the "wonder weapons"....all of those things were under research in US & UK as well. And remember, it was the uS which came up with the A-bomb first. Think we would not have dropped a few on Kiel, Bremerhaven, teh Ruhr, etc.?

And about German development of the A-bomb, Hitler was more focused on developing nuclear reactors for his U-boats than a bomb. When Germany capitulated in 1945, they were still quite a ways from exploding a nuke. And remember, the Manahattan Project was well underway when the U.S. joined the war. Roosevelt was convinced that we needed the A-bomb first, and we still would have gotten it.