Wel Liam i doubt anything could have been done because as soon as the air war was won by Britian (particularly the Battle of Britian) the Germans had no chance in winning battles at sea or trying to disrupt British concoys (Goerings fault). And British planes were xpecialy hunting down U-Boats so not been able to rise out of the water with those flying around was bad and more U-Boats would've been a masacre maybe....