Bribie Island, Australia Oban Bay, Scotland Nahant, Massachussetts

This is the home page for the anti-submarine magnetic indicator loop research project. Indicator Loops are long lengths of cable laid on the seafloor of harbours to detect enemy submarines.  They were developed by the Royal Navy in the early 1900s and first trialled at the end of WW1.  They were then successfully deployed in WW2 in British ports both at home, in the Dominions (Australia, Canada, New Zealand, South Africa, Kenya, Ceylon, Penang) or in allied harbours (Iceland, Holland, Dardanelles). By 1942 the United States had adapted this technology for its own needs.
If you have any feedback please contact me:

Dr. Richard Walding
Research Fellow - School of Science
Griffith University
Home Phone: 61 07 32064976
69 Summit Street, Sheldon, Q, 4157, Australia



  • How an indicator loop works
  • Who made the Loop cables?
  • Harbour Defence ASDIC (HDA)


    Royal Navy
  • Overview of Royal Navy loop stations
  • Oban Bay (Argyll, Scotland)
  • Isle of May (Firth of Forth, Scotland)
  • Bereshaven & Queenstown (now called Bere Is. and Cobh, Ireland)
  • Cromarty (Moray Firth, Scotland)
  • Loch Ewe (North West Scotland). Guard loops and Controlled Mining only.
  • Sheppey Island, Kent) - Shellness and Sheerness: Guard loops and Controlled Mining at  only.
  • Scapa Flow, Orkney Isles
  • Plymouth
  • Portsmouth
  • Portland (HMS Osprey)
  • Penang
  • Cumbrae
  • Rosyth
  • Dunoon
  • Trincomalee (Ceylon)
  • Malta
  • Hong Kong
  • Walcheren Island - Flushing to Breskens (Netherlands)
  • South Africa (Capetown, Durban, East London, Port Elizabeth)
  • Mombasa, Kenya: in Kilindini Harbour
  • Iceland (Hvalfjordhur or Hvalfjordur)
  • Gallipoli (Dardanelles)
  • Royal Australian Navy
  • Overview of Australian loop stations (under construction)
  • Moreton Bay Harbour Defences. These  were located at several naval installations in and around Moreton Bay. The following webpages will be found at the "Moreton Bay"  link.
  • RAN 1: Port War Signal Station (PWSS), "Buena Vista", Wickham Point, Caloundra
  • RAN 2(A): Controlled Mining and Guard Loop Station at Tangalooma;
  • RAN 2(B): Controlled Mining and Guard Loop Station at Fort Bribie;
  • RAN 3: Controlled Mining and Guard Loop Station at Cowan Cowan;
  • RAN 4: Indicator Loop and Harbour Defence ASDIC Station at Woorim, Bribie Island;
  • RAN 5: Combined Training Centre (Naval Wing), Toorbul
  • RAN 6: Advanced Fairmile Base (AFMB), Bongaree, Bribie Island;
  • RAN 7: Indicator Loop and Harbour Defence ASDIC Station at Comboyuro Point, Moreton Island;
  • RAN 8: Boom Defence Facility:Anti-submarine Boom across the Brisbane River between Lytton and Bulwer Island;
  • RAN 9: Indicator Loop and Photo-electric beam Station, Myrtletown;
  • RAN 10: Naval Store, Pinkenba.
  • Also of interest: Fort Bribie, including RAN 2 Controlled Mining Station.
  • Fort Skirmish, Woorim, Bribie Island (Skirmish Battery)
  • Toorbul Radar Station No. 210 run by the RAAF
  • Sydney (Loops, HDA, PE Beam)
  • Fremantle (Loops)
  • Darwin (Loops)
  • Newcastle (Loop and Controlled Minefield)
  • Port Phillip - Victoria (PE Beam)
  • Broken Bay (Loops and Controlled Minefield)
  • Port Kembla (Loop)
  • Port Stephens (Loop)
  • Botany Bay (Controlled Minefield)
  • Port Moresby (Indicator Loops)
  • Royal New Zealand Navy
  • Auckland, Wellington & Christchurch
  • Royal Canadian Navy

  • Overview of indicator loops in Canada
  • Saint John
  • Antisubmarine School at Digby (Nova Scotia)
  • Prince Rupert (Port Edwards)
  • United States Navy
  • Overview of loop receiving stations in the USA
  • 1A Bailey Island, Casco Bay (Maine)
  • 1B South Portland at Cape Elizabeth - south-eastern end, overlooking Casco Bay (Maine)
  • 1C North Scituate, Rhode Island (Massachusetts)
  • 1D Nahant, East Point (Massachusetts)
  • 1E Gloucester, 25 mi N of Boston (Massachusetts)
  • 1F Peaks Island & Fort Williams Peaks Island - later transferred to Fort Williams (Maine)
  • 1G Portsmouth (NH) at the Navy Yard
  • 1I South Westport (or Westport Point) - between Fort Rodman and US Naval Base at Newport (Massachusetts)
  • 1X Argentia - Naval Base (Newfoundland)
  • Fort Tilden New York Harbor Entrance Control Post (HECP)
  • Woody Island Kodiak (Alaska)
  • Espiritu Santo
  • HECP Fort Story, Cape Henry, Virginia
  • HECP Fort Windfield Scott, San Francisco, California
  • HECP San Pedro, California
  • Ocracoke, North Carolina
  • Panama