Sydney Harbour anti-submarine boom net

The Sydney Harbour anti-submarine boom net was an anti-torpedo and submarine defence net that was in Sydney Harbour during World War II. It spanned the entire width of the harbour from Green Point, Watsons Bay to Georges Head, on the northern side of Sydney Harbour. The boom formed part of the Sydney Harbour defences which also included artillery batteries and patrol boats.

Construction of the boom commenced in January 1942 and the boom and gates were fully operational by August 1942. For over three years, entry to Sydney Harbour was restricted by the boom net. All vessels including ships, ferries and fishing boats gained access to the harbour via one of three gates in the anti-torpedo and anti–submarine boom which spanned the harbour from Green Point to Georges Head.

On the night of 31 May 1942, three Japanese midget submarines attempted to enter the harbour in what became known as the Attack on Sydney Harbour. On the night of the attack the central section of the net was complete and support piles were in place to the west, but there were gaps of up to 400 metres (1,300 ft) wide on either side of the boom net. Material shortages, not lack of interest, prevented the completion of the boom net prior to the attack. The first submarine, the M 27, commanded by Lieutenant Jahai Chuma, was the first submarine to attempt entry. The M 27 followed another vessel into the harbour, but at some stage became entangled in the western end of the boom net's central section. Lieutenant Chuma tried to free his submarine by using a sawtooth metal cutter, which only entangled it further. By 8.30 pm he had attracted the attention of the watchman for the Maritime Service Board, James Cargill, who rowed across in a boat and discovered the Japanese submarine. Surprised, Cargill radioed naval headquarters. It took him two hours to convince the navy that there was a Japanese midget submarine caught in the boom net.

At 10:27 pm Chuma, realising that he had been detected, detonated charges, destroying the submarine and killing himself and his crew in the process. The two other midget submarines penetrated the then only partially completed boom net, and attacked shipping for several hours before being destroyed.

The boom net was removed after the end of the war in August 1945, and by early 1946, everything apart from the dolphins had been removed. The foundations of the winch house are the only remaining evidence of the anti-submarine boom net and they can still be seen on the shores of Green Point, along with other remaining evidence of military installations, such as underground fortifications and bunker complexes.

...
Wikipedia