[Nokose]

Brian,
It probably had something to do with the type cargo that they were carrying and where they were going. I've read that neutral ships still ran during the night with all their running lights on and from many accounts U-Boats and surface raiders made no attempt to stop them. If they were stopped and there was contraband on the the manifest it wasn't a good thing for them. Also sailing alone on prearranged route didn't mean much as the British merchant fleet still ran fast single ships and would probably be sent along these same routes. The book about U-Boat ace Otto Kretschmer described searching neutral ships traveling in 1939 and 1940 coming from Sweden. The Germans at that time hadn't perfected their contraband list and gave their cargo as "Lumber" which wasn't on the list.