April 1945... it was probably an italian vessel which attacked you as italy had already surrendered. Though some italian forces continued to fight along side germans in the field, most of the italians turned against germany.
My guess, though germany held onto your port, the italian navy patrols those waters heavily and you just got into some hard luck.
this makes sense because the italian anti submarine trawler would have been close to the italian coastal waters, and with less than a month remaining in the war... italty had long since been an enemy of germany.
also watch out for this in france, a couple of french ports hold out until almost to the bitter end, though the port is blue and you can dock there... the area is packed with enemy planes and ships
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