Destroying a merchant ship that's crossing the Atlantic isn't that hard, just as it's not that hard to destroy a troop barge that's crossing the channel. Our Navy could easily have destroyed an invasion fleet.The Navy was losing the merchant war at sea until it changed it's tactics
Firstly, the Germans were never winning the Battle of Britain - they weren't shooting enough of our aircraft down, they weren't ever putting our airfields out of action, and we continued to build as many fighters as we lost. Secondly, even if they had been winning it, we only needed to retreat north and sit back, ready to bomb the shit out of any invasion fleet. Germany never had a chance.the German's were winning the BoB until they changed theirs