Anti-submarine indicator loop
Encyclopedia
An anti-submarine indicator loop was a submerged cable laid on the sea bed and used to detect the passage of enemy submarines. Developed by the Royal Navy
during World War I
, they were extensively used by the Allies during World War II
to protect harbours against submarine attack.
They worked as induction loop
s – the submarine's magnetism induced a current in the cable as the submarine passed across it. The technology was first developed and trialled at the British Admiralty's Board of Investigation and Research at Harwich on the Essex coast in England. The first operational use was at the Grand Fleet's anchorage at Scapa Flow
. The German submarine UB-116 was detected by hydrophones at 21:21 on 28 October 1918 attempting to enter the harbour and anchorage via Hoxa Sound. Two hours later (at 23:32) current was detected in an indicator loop laid in a remotely controlled minefield, induced by the submarine as it passed over the cables. Mines around the loop were detonated by remote control, sinking the submarine. It was the last U-boat destroyed by enemy action before the Armistice. After the war, indicator loop devices were further developed by the Admiralty's research divisions at HMS Vernon and HMS Osprey (Portland Naval Base). In WW2 indicator loops were used by the Allies for harbour defence in the UK and it's dominions and protectorates, as well as by the US Navy.
Royal Navy
The Royal Navy is the naval warfare service branch of the British Armed Forces. Founded in the 16th century, it is the oldest service branch and is known as the Senior Service...
during World War I
World War I
World War I , which was predominantly called the World War or the Great War from its occurrence until 1939, and the First World War or World War I thereafter, was a major war centred in Europe that began on 28 July 1914 and lasted until 11 November 1918...
, they were extensively used by the Allies during World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
to protect harbours against submarine attack.
They worked as induction loop
Induction loop
Induction loop is a term used to describe an electromagnetic communication- and detection system, relying on the fact that a moving magnet will induce an electrical current in a nearby conducting wire. Induction loops are used for transmission and reception of communication signals, or for...
s – the submarine's magnetism induced a current in the cable as the submarine passed across it. The technology was first developed and trialled at the British Admiralty's Board of Investigation and Research at Harwich on the Essex coast in England. The first operational use was at the Grand Fleet's anchorage at Scapa Flow
Scapa Flow
right|thumb|Scapa Flow viewed from its eastern endScapa Flow is a body of water in the Orkney Islands, Scotland, United Kingdom, sheltered by the islands of Mainland, Graemsay, Burray, South Ronaldsay and Hoy. It is about...
. The German submarine UB-116 was detected by hydrophones at 21:21 on 28 October 1918 attempting to enter the harbour and anchorage via Hoxa Sound. Two hours later (at 23:32) current was detected in an indicator loop laid in a remotely controlled minefield, induced by the submarine as it passed over the cables. Mines around the loop were detonated by remote control, sinking the submarine. It was the last U-boat destroyed by enemy action before the Armistice. After the war, indicator loop devices were further developed by the Admiralty's research divisions at HMS Vernon and HMS Osprey (Portland Naval Base). In WW2 indicator loops were used by the Allies for harbour defence in the UK and it's dominions and protectorates, as well as by the US Navy.