The key map is number 4 where you see the German tanks make it back to Germany/Norway. Taking the transports out with planes to prevent this is the obvious solution but it may be more difficult if Italy has a navy. If you lose Gib on round 1 and Italy has a navy then you may not be able to defend seazone 102. Remember if the carriers take hits the planes sink. If USA Builds bombers instead then you make sure they cant land by taking Eire and consolidate the navy with the German navy.
There is obviously mistakes by both sides in this game but I’m just using it as an example. The best way to defeat Sealion is to avoid it all together by defending London and Gib on round 1.