This is a rather simple idea I had..
You can see on your lionesses page how many hunts she has had and how many were successful. Why not do the same for subs but with patrols?
This way people who want to buy a sub can look for ones that are successful even if whether or not they are successful is random. Just for fun :D

Suggestion by Cinderblaze: # stats gained on patrol should also be shown as even if your sub gains stats but doesn't bring anything back it is considered unsuccessful.