With the combined might of the RAF Fighter Command, Britain falied to achieve air superiority over Dunkirk because the bases were in Britain and Dunkirk is across the Channel. By the same token, the Luftwaffe failed to achieve air superiority over Dunkirk because their fighter bases hadn't been moved closer, and were under similar range constraints. The RAF was a short range defensive force by plan, tailor-made to defend Britain, and backed by a warning network designed by Dowding to achieve a victory by defense in the BoB. The counter to this would have to be an effective strategic long-range Luftwaffe, with heavy bombers and long-range fighters. The Bf-109 had an endurance of about one hour. The bombers were all medium bombers with poor defensive armament, intended for tactical, not strategic roles. To imagine a victory for the Luftwaffe in the BoB, something is missing. Beyond that, the Luftwaffe wasn't all that ineffectual in the anti-shipping role, but again, hadn't created effective weapons nor undergone effective training for the purpose, and wasn't that great either. Most noteworthy was the lack of an effective air-launched torpedo.