AROUND THE WORLD

Anti-submarine Indicator Loop stations in the United States
Portsmouth Loop Receiving Station

Appledore Island

Drawing by Gerry Butler

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. This webpage looks at the indicator loop defences in Portsmouth Harbor, New Hampshire, USA.

If you worked there, or at any USNLRS, or have any feedback please contact me: Dr. Richard Walding (Email: waldingr49@yahoo.com.au) Research Fellow - School of Science Griffith University, Australia Home Phone: 61 (0)7 32064976 69 Summit Street, Sheldon, Q, 4157, Australia

Anti-submarine Indicator Loops
Indicator Loops are long lengths of armoured cable laid on the seafloor of harbors 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 successfully deployed in WW2 in British ports and other Commonwealth countries such as Australia, Canada, New Zealand, South Africa, Kenya, Ceylon, Penang, and in allied harbours (Iceland, Holland, Dardanelles). By 1942 the United States had adapted this technology for its own needs and a dozen United States Navy "loop receiving stations" were established along the eastern seaboard of mainland USA particularly at the ports of Boston and Portland. The Pequot was the main cablelayer for the USN's indicator loop harbor defense. The deployment of indicator loops was highly secret and hardly any of the men on the ship knew the purpose of the cables; most thought they were underwater communications cables. The words indicator loop were not used - just cable. The sailors manning the loop huts were given rudimentary (3 week) training in harbor detection by indicator loops and sono-radio-buoys. To find out more about the role of the Pequot go to the USCG cableship Pequot webpage.

This diagram shows the arrangement of the cables in the loop ("3-legged") and the tail cable connecting them to the shore station. The Pequot crew laid the four loop cables at Boston in the correct position and joined it to the tail cable from East Point or Strawberry Point using waterproof splices and junction boxes.