 They took part in fleet actions and they worked in smaller groups and singly to harry enemy supply lines.Late in the Pacific War when large targets became scarce, many PT boats replaced two or all four of their torpedo tubes with additional guns for engaging enemy coastal supply boats and barges, isolating enemy-held islands from supply, reinforcement or evacuation.The most significant military ship sunk by a torpedo boat during World War II was the cruiser which was attacked by two Italian torpedo boats (M.S.