Oh, and another fix worth adding: When one of the official game patches raised visibility to 20k metres, suddenly some of the single missions became unplayable (F.e. Tokyo Saipan convoy) because they were originally scripted with the sub much closer to the enemy so a contact would be done. Now the enemy spots you as soon as the mission starts and you are already detected
Should be fixed easily with the mission editor, either by moving the sub away or simply submerging it.