Thames Boom, Medway Gate, being opened.

The Thames Boom was over six miles long, had two gates, the Medway Gate  on the Medway channel leading into Sheerness and the River Medway and the Yantlet Gate on the Yantlet channel leading to the Thames and London.


To the Thames estuary Boom were added “Indicator Loops”. Indicator loops were also placed at the mouth of the Swale at the east end of the Isle of Sheppey at Shellness and at the mouth of the Medway at the west end of the Isle of Sheppey at Garrison Point, Sheerness.

Indicator Loops where Top Secret during WW2 and for a long time after, but were regularly used to protect Allied harbours around the World. Indicator Loops are known to have been installed at Capetown, South Africa and Darwin and Sydney, Australia. Although at Sydney, when a midget Japanese submarine entered the Harbour it was thought to be an equipment malfunction.

Indicator Loops together with a barrage of mines were also set up across the Straights of Dover to prevent German Submarines using it as a short cut to their bases in Germany. On the 8th October 1939 the Dover Mine Barrage and Indicator Loops had its first victim when the German U-boat U12 was sunk with the loss of all 27 crew. Only five days later the Dover Mine Barrage and Indicator Loops claimed its second victim when the U40 was also sunk with the loss of 45 of her 48 crew. This bought an end to German U-boats using the Straights of Dover as a route to their home bases.

Indicator Loops were first used during the First World War (1914 to 1918) at Scapa Flow, a Naval Base in the Orkneys from which the Royal Navy could control the North Sea. Indicator loops detected the German submarine UB116 as it passed over it. It was depth charged and sunk with the loss of all 36 crew.

Between the Wars, indicator loops were further developed by the Admiralty's research divisions at HMS Vernon at Portsmouth and HMS Osprey at Portland. Indicator Loop are electrical cable laid on the seabed connected to a control station on shore.

During manufacture a large iron structure such as a ship or submarine become mildly magnetic due to the Earths magnetic field. When they pass over the Induction Loop cable a low charge is transmitted along the cable to the control station instruments.

Behind the Indicator Loops at Sheerness and Shellness were laid “Observation Minefields” These were armed with World War One explosive torpedo heads connected to a wire and could be detonated by an observer on shore. In addition six torpedo tubes were installed on shore at Sheerness.

Remains of Thames Boom as it is today, Isle of Sheppey.

The Thames boom was operated by fourteen trawlers and tugs, five unpowered lighters, and five civilian manned launches and employed over four hundred people.

Life on a Boom Vessel could also be hazardous. On the Dec 17 1940 HMT THOMAS CONNOLLY the Thames Boom Defence Vessel, out of Sheerness, struck a mine and sunk north of Sheerness  with the loss of 17 of her crew. T/Lt R. L. Langridge RNVR, was lost in the vessel and T/Boom Skipper Martell was wounded.

On the 22nd Sep 1943 HMT OCEAN RETRIEVER, Harbour defense vessel, out of Sheerness, struck a mine and sunk in the Thames Estuary. All of her 11 crew were lost.

RISTANGO fouled the boom and sunk in Nov 1940.

Boom Gate Vessels:  BV1  (Boom Vessel) BV2, BV5, BV10, BV18, CORONATIA, FIELDGATE, and MOORGATE.


Boom Defence Tug: HARTY and KESTREL.

Boom Defence Tenders: Naval auxiliary boats COLONIA, GLITTER II, QUEEN OF SOUTH I, QUEEN OF SOUTH II and SILVEEN. 

Posts and vessel sunk in the shallow water on the Sheppey side of the Thames Anti-submarine Boom.

​Click Here.

The Thames boom as it was 1939 to 1945

Anti-submarine/anti-​Schnellboot, boom float  similar to those on the Thames Boom.

E-boat, German Schnellboot, fast torpedo boat.

Anti-submarine and Anti-E-boat net.

To protect to convoys of merchant shipping and Royal Navy ships in the Thames Estuary during World War Two (1939 to 1945) an anti-submarine net was placed across the Thames Estuary from the Isle of Sheppey in Kent to Shoeburyness in Essex. At the outbreak of war booms were installed across the Humber, at the entrance to Harwich and across the Thames Estuary.

HMT Thomas Connolly, Boom Defence Vessel, crew lost.

BARNES, Robert, Act/Rigger's Mate, R/JX 180720, MPK
BLACKMAN, Ralph D, Steward, C/LX 23365, MPK
BRODIE, John, Act/Rigger's Mate, R/JX 196522, MPK
CHAVE, Henry, Chief Petty Officer Stoker, D/K 474, (Wildfire, O/P), MPK
EDMUNDSON, James, Stoker 1c, R/KX 102238, MPK
EVANS, David E, Stoker 2c, R/KX 102242, MPK
GRAHAM, William B, Act/Rigger's Mate, R/JX 196520, MPK
HANCOCK, Alfred, Stoker 2c, R/KX 100794, MPK
HARKER, Ralph R, Stoker 2c, R/KX 100880, MPK
HARVEY, James, Chief Petty Officer Stoker, C/208315, MPK
JEHU, John, Ordinary Seaman, R/JX 213376, MPK
LANGRIDGE, Richard L, Ty/Lieutenant, RNR, MPK
MACLEAN, Donald J, Act/Rigger's Mate, R/SR 76230, MPK
MACLEAN, John R T, Act/Rigger's Mate, R/SR 76244, MPK
RICHARDSON, James W, Stoker 1c, R/KX 100793, MPK
WARMAN, Arthur L, Ordinary Seaman, R/JX 213327, MPK
WARREN, Ernest E, Stoker Petty Officer, C/K 2690, MPK

Thames Boom showing the Medway and Yantlet Gates, Induction loops and the now demolished Nore Sea Fort.


South east England and the Thames Estuary was within easy reach of the German E-boats operating out of captured Dutch ports. This necessitated the construction of the Thames Boom being, in addition to an anti-submarine boom,  an Anti-motorboat Boom.

This requires the floats being built in a robust manner of heavy iron-strapped timbers, joined together with heavy chains and fitted with watertight iron floats