Thanks for the info; I assumed they could be sinking non-neutral (non US) ships along our coast before the war. The early days of the war against us were called the “happy times” by U-boat crews; their operation “Drumbeat” involved getting as many ships over here as quickly as possible because our freighters were sitting ducks.
When my father was a child in NYC they had blackouts; officially they were told it was to prevent ships from being silhouetted against the city lights. After the war it was revealed that it had been done to prevent NYers from seeing the damaged ships come in (with the related implications for public morale).