Royal Navy | Harbour Defences in the Cromarty Firth | South Sutor | Scotland 

Dji Pocket 2
Canon EOS 4000D.
Lens 18-55mm.
indicatorloops...
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.