I recall in the earlier builds of the game that there was always a notification that informed you how much damage your submarines have managed to inflict upon the Entente blockading fleets.
This, it appears, has vanished ever since.
I'd reckon it'd be a good idea to include them back again and ALSO when a submarine gets destroyed while in strategic warfare. I remember that at the beginning of the CP campaign Germany at 3 subs....as the war went on it only had 2 subs and so on. Without me actively checking I would have believed that my submarines are doing the job unknowingly that the Entente might have already destroyed them all.
Care to include the messages again, please?