On 31 May 1942, during WWII, three Japanese submarines tried to get into the harbour. The first submarine to try and come in was the M27. Lieutenant Jahai Chuma was the man in charge of this submarine. The M27 followed a Sydney ferry through the gate on its way to Manly, but it got caught in the western end of the net's middle section. Lieutenant Chuma, tried to free his submarine by using a special tool that cuts metal, but this only made things worse. By 8:30pm the watchman for the Maritime Service Board, James Cargill, went to see what was happening. He used a boat to row across to where the submarine was stuck. Very surprised at finding a Japanese submarine, Cargill called naval headquarters with his two way radio. At first the navy did not believe that there was a Japanese Midget submarine caught in the boom net. It took him two hours to get them to believe him.