You also had a natural current passing through the Gibraltar strait.
One from the Atlantic towards the Mediterranean
A uboat could turn off the engines. And use the current to slip inside.
But uboats trying to get in the Atlantic had real trouble, they were forced to use there engines. There engine powers had also little speed.
Thats why there is no recordings, of a German uboat crossing Gibraltar to enter the Atlantic.
Correct me if i'm wrong
