I was going to propose that the Germans and Russians could have done exercises along the Black Sea to gain experience with the logistics and execution of amphibious landing. Then the truth of FramerT's comment about them hating each other sank in. Lets say that they didn't hate each other so extensively. This is what if.
Starting early in 1939 German officers and men in the strength of about a division, with all of their equipment, move to the shores of the Black Sea in Russia. There they begin training and practicing how to move across water. The Russians provide assistance by hosting the soldiers and by providing them with the output of manufacturing facilities to create their landing craft. Toward the end of the experiments they would provide scenario defenders to oppose the landing practices.
Then when the Germans have learned what they needed for their assault on England the German Division could spearhead Barbarossa from behind enemy lines. SUPRISE!
