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The Boom Net that protected Darwin

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While the Territory’s World War II history is dominated by the air raids on Darwin and beyond, it was in the ocean that the town had a silent defender at work – a 6km boom net to keep enemy vessels out.

In 1937 the Royal Australian Navy recognised that the Darwin port would need defence against incoming enemy vessels – including submarines – and so work began on the installation of the boom net across the harbour. At six kilometres in length it was the longest in the world, and ran between Dudley Point, near East Point, and West Point, near Mandorah.

The boom net consisted of cable carried on the surface and strung from buoy to buoy. There were two types of buoys, large cylindrical models tied to concrete moorings below, and barrel-shaped flotation buoys supporting steel netting. Ship-operated gates let friendly vessels through. Two purpose-built boom vessels, HMAS Kookaburra and HMAS Koala, arrived in April 1940 and Darwin’s sea defence was finally in place.

HMAS Koala’s sister ships, Kangaroo and Karangi, joined the effort, as eventually did Tolga, Kara Kara, Koompartoo, Terka and Gunbar. The work was monotonous and unrewarding, but totally necessary, as evidenced by the lack of penetration by enemy vessels through the entire war. 

When the Japanese attacked on 19 February 1942 the first vessel engaged was boom vessel HMAS Gunbar. Her commander, Lieutenant Norman Muzzell RAN, saw incoming Zero fighters successfully engaging a US Kittyhawk and altered course to pick up the allied pilot. 

Post-war the boom was dismantled. Its eastern starting point can still be seen at Dudley Point. The mooring blocks remain on the harbour sea floor and the wharf from which the boom net vessels operated just north of the present Darwin wharves has now been dismantled.

​A boom ship at work in Darwin Harbour. The two "horns” allowed floats to be winched up to be repaired. (RAN)