From Roscoe Creed’s PBY: The Catalina Flying Boat:
In May a campaign was launched to free the Bismarck Archipelago of Japanese domination, and the [Australian] Catalina squadrons were called on for more bombing raids. The Milk Run was expanded t the north; Run “O” being added to Run “M”, mainly to hunt enemy submarines that were operating in increased numbers. Three were bombed in the next several weeks, but none were sunk. Two were Japanese. One was American: The USS Tuna failed to identify herself quickly enough. No. 20 Squadron personnel saw the error as an opportunity to check the effectiveness of their depth charges. A message was sent to the Tuna’s captain requesting information, but for some reason no reply was received.
Perhaps the poor captain wandered into a U.S. Army patrol sector?