Possability they ran as neutrals
Donitz seemed to think they would
Then C-in-C Navy spoke of the conduct of the war in general. He said that the next step he intended to take in the war at sea against England, before declaring unrestricted danger zones, was to declare danger zones only against English ships, not against neutrals. He wished first however, to hear F.O. U/B's views. I replied that in my opinion warfare limited to certain nations would not bring the desired results, because:
1)In most cases the U-boat, which has to wait submerged for a suspicious ship, cannot identify the ship's nationality in time to attack without warning.
2)Presumably the enemy would very soon sail his merchant ships under the protection of neutral markings and flags.
The results would be:
a)either many neutrals would be sunk without warning as supposed enemies, which is just what we want to avoid
b)or many enemy ships would get away as supposed neutrals, which we want to avoid ever more.
http://www.uboatarchive.net/BDUKTB30248.htm