There were not "milk cows" - there were not submarines but only standard small tankers or supply merchants. In the early years of the war the III Reich had supply fleet to refit submarines and other German raiders - in fact, after Enigma decryption all these supply ships (located at open see) were found and destroyed.
In my opinion the option "end patrol" should be deleted - these ships (and milk cows in later years of war) allow only refit to uboat in fuel, ammo and food (morale grow?).
End patrol should be available only in German home base.
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