in the United States

Drawing by Gerry Butler

 One highly secret method of the past used to detect submarines relied on magnetic properties of submarines and surface vessels is the anti-submarine indicator loop. These loops of cable are laid on the ocean floor in shipping channels and when a submarine passes overhead an induced current is produced and this is detected on the galvanometers at the nearby shore station. Even if wiped or degaussed, submarines still have sufficient magnetism to produce a small current in a loop. This page details the history of indicator loops in the USA during WW2.

If you have any feedback please email me:

Dr Richard Walding  
Research Fellow - School of Science
Griffith University
Brisbane, Australia
 Email: waldingr49@yahoo.com.au


What are Indicator Loops?
 Submarines may be detected by many methods but one highly secret method of the past that relied on magnetic properties of submarines and surface vessels is the anti-submarine indicator loop. It relies on the production of an induced current in a stationery loop of wire when a magnet (in this case, a submarine) moves overhead. Even if wiped or degaussed, submarines still have sufficient magnetism to produce a small current in a loop. The technology was developed by the British Royal Navy in 1915. It was sent to various Commonwealth countries (Australia, Canada, New Zealand) for deployment. With the close technical co-operation between the Royal Navy and the US Navy, the indicator loop technology was enhanced for use in the US from about 1942 onwards. In the US, the control stations were known as 'loop receiving stations' and were a part of the Harbor Entrance Control Post (HECP). The first loop installation in the US was made at Cape Henry, Virginia in summer 1941, although hydrophones had been trialled at Fort Wright (Fishers Island, NY), Nahant (Boston) and Fort Story (Virginia) in 1918. Units (loops, hydrophones, heralds) were installed in practically every major and medium continential US harbor in the few months after August 1942 and by the end of 1942 were being shipped to the South Pacific. Underwater detection was installed in major and medium ports along the east and west coast of the US, the Aleutians, South Pacific, Central Pacific, France, Philippines, the Canal Zone (Bahia de Panama), Australia and South America. At the time of surrender, several units were ready in California to be shipped to Japan.

Today, more than 50 years after the war, many of the countries that still have US Navy loop cables are having them removed for a variety of reasons. One is that many ports are expanding or having their harbors dredged deeper to accommodate today’s larger ships. The cables are an obstacle to dredging operations and a potential hazard for ships anchoring. The other reason is their enormous scrap value. Most of the cables were constructed of copper, but with copper in such short supply during the war years, some were actually made of silver with the intent of reclaiming them after the war. However, very little salvage was ever done. Consortiums of private investors and government officials are now being formed to locate and remove these cables. (One of the companies performing this service is Resolve Marine Group in Port Everglades, FL. Resolve has been providing a variety of marine services to companies and government agencies in the U.S., Central and South America, and throughout the Caribbean for the past 20 years).

The loop locations
 The following Harbor Entrance Control Posts all had loop receiving stations attached. The list below shows many of the HECPs and their naval unit codes. About 50 were set up by the United States Navy along the East and West Coasts of the US, The Aleutian Islands, South Pacific, North Africa, Sicily, Italy, SW Pacific, Central Pacific, France, Phillipines, Canal Zone and South America. Links will take you to separate pages for some of the stations I have details for.
1st Naval District  
  • Casco Bay (Portland, Maine): 1A Bailey Island, 1B South Portland (Cape Elizabeth), 1F Peaks Island/Fort Williams
  • 1C North Scituate (Fourth Cliff to Provincetown, Massachusetts); and Rhode Island (Massachusetts)
  • 1D Nahant, East Point (Boston, Massachusetts)
  • 1E Gloucester, 25 mi N of Boston (Massachusetts)
  • 1G Portsmouth (Appledore Island, Maine
  • 1H Fort Burnside
  • 1I South Westport at Goosebury Neck (or Westport Point) - between Fort Rodman and US Naval Base at Newport (Massachusetts)
  • 1X Argentia - Naval Base (Newfoundland)
    		•
        3rd Naval District
  • Fort Tilden New York Harbor Entrance Control Post (HECP)
  • Spermacetti Cove (New Jersey)
  • Fort Wright - Fishers Island (HECP)

    •     4th Naval District

  • Fort Main Naval Station (Delaware)

    •     6th Naval District

  • Ocracoke Naval Station (North Carolina)
    •     15th Naval District
  • Panama
    •    17th Naval District
  • Woody Island Kodiak (Alaska)
    •  

    Many HECPs were established at critical harbors on the Atlantic and Pacific coasts of the United States and it's territories. Most, but not all had loop defenses. Here is a list of some other HECPs:
    District # ---- Station ----- Location ----------- Latitude - Longitude
    1 -- Portland, ME -- Fort Williams -- (N43-37-15, W70-13-00)
    1 -- Portsmouth, NH -- Ex-Coast Guard Station (Fort Stark, Battery Kirk) -- (N43-02-30, W 70-42-00)
    1 -- Boston, MA -- Fort Dawes -- (N42-21-30, W57-30)
    1 -- Newport, RI -- Beavertail -- (N41-27-00, W71-24-00)
    3 -- Fishers Island -- Fort HG Wright -- (N41-15-22.8, W72-01-23.9)
    3 -- Staten Island, NY -- Fort Wadsworth -- (N40-36-15, W74-03-22)
    4 -- Delaware -- Cape Henlopen (Fort Miles) -- (N38-47-39, W75-05-32)
    5 -- Norfolk, VA -- Just outside Fort Story -- (N36-55-48, W76-00-42) - Cape Henry, Virginia
    6 -- Charleston, SC -- Fort Moultrie -- (N32-45-33, W79-51-31)
    7 -- Key West, FL --
    7 -- Florida, Experimental Harbor Underwater Detection Station, Ft Lauderdale.
    8 -- Santa Rosa Island, FL -- (Fort Pickens, Battery Worth) -- (N30-19-30, W87-17- 30)
    8 -- Galveston, TX -- Fort Point (Fort San Jacinto) -- (N29-20-00, W94-44-37)
    10 -- San Juan, PR -- (Fort Brooke, El Morro) -- (N18-28, W66-07)
    10 -- Vieques Sound (Roosevelt Roads), PR -- Punta Algodones
    11 -- San Diego, CA -- (N32-40-19, W117-14-24)
    11 -- San Pedro, CA -- Fort MacArthur (Battery Leary and Merriam) (N33-42-42, W118-17- 32) - practice loop in East Channel
    12 -- San Francisco, CA -- Fort Winfield Scott (Dynamite Battery) -- (N37-48-08.3, W122-28- 32.7)
    13 -- Columbia River -- Fort Stevens (Battery Mishler) -- (To be established)
    13 -- Puget Sound Area, WA -- Fort Worden -- (N48-08-30, W122-46-00)
    14 -- Pearl Harbor, HI -- Navy Yard Pearl Harbor -- (N21-21-11.9, W157-57-26.2)
    15 -- Cristobal, Panama Canal Zone (Atlantic Side) -- Fort Sherman -- (N9-22-00, W79-57-00)
    15 -- Balboa, Panama Canal Zone (Pacific Side) -- Fort Amador -- (N8-55-00, W7931-00)
    16 -- Manila Bay, Corregidor -- Fort Mills -- (N14-22-59, E120-34-23)

    Cableship

  • USGC Pequot - a special page of photos detailing life aboard the indicator loop laying and repair cableship Pequot.

    • LINKS TO RELATED PAGES:

  • Indicator Loops around the World (Home Page)
  • How an indicator loop works
  • Bribie Island (Australia) Indicator Loop Station (RAN)
  • Oban Bay, Scotland, Indicator Loop Station (RN)
  • The interpretation of the signature and some more examples can be found at: Reading Loop Signatures.