It should be a lot harder to hit ships than it is currently.
It should be easier to set up a good torpedoe run. 1 torp hit should temp disable the ship. (engine damage/flooding)
2 and its speed should be cut in half.
Ships are too fast by half.
Yes some ships in WWII did 30 mph for short bursts, but if they ran that fast for more than 12 hours they outran their fleet oilers. Then the whole fleet sat till they caught up. If they were still alive that is.
Last, we need a lot more coastal shipping.
Frieghters, oil tankers, minesweepers, stuff that moves 6 - 10 mph and is lightly defended if they have any guns at all.