In 1942 during the Second World War the Sydney Harbour anti-submarine boom net was constructed on Georges Head and was designed to prevent enemy submarines from entering into Sydney Harbour. The boom net spanned the entire width of Port Jackson and a boom net winch house was located on Liangs Point, Watsons Bay. On the night of 31 May 1942, three Japanese midget submarines attempted to enter Sydney Harbour in what became known as the Attack on Sydney Harbour. One of the Japanese midget submarines became entangled in the boom net and after unsuccessful attempts by the crew to free the submarine they detonated charges within the sub, killing themselves and destroying their sub in the process.