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The Royal Australian Navy approved the construction of anti-submarine defences for Moreton Bay on 22 June 1942.

HMAS Bangalow completed laying four Indicator Loops and three Harbour Defence Asdic (HDA) systems across the entrance to Moreton Bay by 24 December 1942. The Bribie Island Indicator Loops were commissioned on 5 February 1943. An Indicator Loop Hut known as RAN4 was established at Woorim on Bribie Island and the Indicator Loops were commissioned on 5 February 1943.

On 3 February 1943 it was decided to lay another Indicator Loop from Myrtletown to Fisherman's Island along with a Photo Electric Beam across the Brisbane River. HMAS Bangalow completed installing the Indicator Loop on 2 March 1943, while the PE Beam was finished on 28 September 1943. RAN 9 Pinkenba Indicator Loop Control Station located at Myrtletown commenced operation on 8 January 1944.

A decision was made on 31 July 1944 to remove the seaward defences for Moreton Bay. This included:-

- Harbour Defence Asdic (HDA) systems
- The Controlled minefield
- The Indicator Loops
- The Obstruction to the South Channel

The Outer Indicating Loop Control Station at RAN4 on Bribie Island ceased its watchkeeping operations on 3 August 1944 and at the same time HMAS Bangalow raised the Outer Indicator Loops and the HDA's.

It was decided on 1 June 1945 to remove the Indicator Loop in the Brisbane River. HMAS Limosa removed this loop on 2 June 1945.


Fort Bribie

Fort Rous

Fort Cowan Cowan

RAN4 - The Bribie Island Indicator Loop Hut
Part of the Royal Navy's anti-submarine harbour defence for "Fortress Brisbane"

HMAS Tambar hit by "Friendly Fire" from Cowan Cowan, Moreton Island

Was American Submarine USS Triton
accidentally sunk in Moreton Bay by friendly fire?




I'd like to thank Richard Walding, the Head of Science Department, Moreton Bay College for his assistance with details on RAN4.



Worledge, G.R., "Contact! - HMAS Rushcutter and Australia's Submarine Hunters 1939-1946", The Anti-submarine Officer's Association, 1994


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Australian Coastline mined during WW2 by the Allies, the Japanes and the Germans

Demolition of our Harbours and Airfields

Defence of Townsville Harbour

American Submarine SS-201 USS Triton, was it sunk by friendly fire?    


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 Peter Dunn 2002

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This page first produced 13 December 2000

This page last updated 02 April 2002