Minesweeping

For the removal of land mines, seedemining.

AnMH-53EfromHM-15tows a minesweeping sled while conducting simulated mine clearing operations.

MinesweeperUSSTideafter striking a mine offUtah Beach,7 June 1944. Note her broken back, with smoke pouring from amidships.

Minesweepingis the practice of removing explosivenaval mines,usually by a specially designed ship called aminesweeperusing various measures to either capture or detonate the mines, but sometimes also with an aircraft made for that purpose. Minesweeping has been practiced since the advent of naval mining in 1855 during theCrimean War.The first minesweepers date to that war and consisted of British rowboats trailinggrapnelsto snag the mines.

By ship

A sweep is either a contact sweep, a wire dragged through the water by one or two ships to cut the mooring wire of floating mines, or a distance sweep that mimics a ship to detonate the mines. The sweeps are dragged byminesweepers,either purpose-built military ships or convertedtrawlers.Each run covers between 100 and 200 meters (330 and 660 ft), and the ships must move slowly in a straight line, making them vulnerable to enemy fire. This was exploited by the Turkish army in theBattle of Gallipoliin 1915, when mobilehowitzerbatteries prevented the British and French from clearing a path through minefields.

If a contact sweep hits a mine, the wire of the sweep rubs against the mooring wire until it is cut. Sometimes "cutters", explosive devices to cut the mine's wire, are used to lessen the strain on the sweeping wire. Mines cut free are recorded and collected for research or shot with a deck gun.Before theFirst World War,theImperial Russian NavyofficerPyotr Kitkininvented "mine protectors" to break a sweeping wire before it could cut the mine's mooring wire.

Minesweepers protect themselves with anoropesaorparavaneinstead of a second minesweeper. These are torpedo-shaped towed bodies, similar in shape to aHarvey Torpedo,that are streamed from the sweeping vessel thus keeping the sweep at a determined depth and position. Some large warships were routinely equipped with paravane sweeps near the bows in case they inadvertently sailed into minefields—the mine would be deflected towards the paravane by the wire instead of towards the ship by its wake. More recently, heavy-lift helicopters have dragged minesweeping sleds, as in the 1991 Persian Gulf War.

The distance sweep mimics the sound and magnetism of a ship and is pulled behind the sweeper. It has floating coils and large underwaterdrums.It is the only sweep effective against bottom mines.

During theSecond World War,RAF Coastal CommandusedVickers Wellingtonbombers Wellington DW.Mk I fitted with degaussing coils to trigger magnetic mines.

Modern influence mines are designed to discriminate against false inputs and are much more difficult to sweep. They often contain inherent anti-sweeping mechanisms. For example, they may be programmed to respond to the unique noise of a particular ship-type, its associated magnetic signature and the typical pressure displacement of such a vessel. As a result, a mine-sweeper must accurately guess and mimic the required target signature to trigger detonation. The task is complicated by the fact that an influence mine may have one or more of a hundred different potential target signatures programmed into it.

Another anti-sweeping mechanism is a ship-counter in the mine fuze. When enabled, this allows detonation only after the minefuzehas been triggered a pre-set number of times. To further complicate matters, influence mines may be programmed to arm themselves (or disarm automatically—known asself-sterilization) after a pre-set time. During the pre-set arming delay (which could be days or weeks) the mine would remain dormant and ignore any target stimulus, whether genuine or faked.

When influence mines are laid in an ocean minefield, they may have various combinations of fuze settings configured. For example, some mines (with the acoustic sensor enabled) may become active within three hours of being laid, others (with the acoustic and magnetic sensors enabled) may become active after two weeks but have the ship-counter mechanism set to ignore the first two trigger events, and still others in the same minefield (with the magnetic and pressure sensors enabled) may not become armed until three weeks have passed. Groups of mines within this mine-field may have different target signatures which may or may not overlap. The fuzes on influence mines allow many different permutations, which complicates the clearance process.

Mines with ship-counters, arming delays, and highly specific target signatures in mine fuses can falsely convince a belligerent that a particular area is clear of mines or has been swept effectively because a succession of vessels have already passed through safely.

By aircraft

AnMH-53Eof the United States Navy towing an MK105 mine sweeping sled

Aircraft can also be used for minesweeping. During the Second World War, fifteen BritishVickers Wellingtonbomberswere modified to carry a largemagnetic inductionloop and anelectrical generator.The "Directional Wireless Installation" (DWI), a cover story for the true purpose of the magnetic loop, was used successfully on 10 May 1940, to sweep a path for the escape of theDutch royal familyto the UK. The DWI was used most successfully in theMediterranean Theatre,particularly over theSuez CanalandAlexandria Harbour.Their use revealed the limitations of the technique, in that it only works effectively in very shallow water (such as canals and harbours). From about 1943,GermanJunkers Ju 52transportswere similarly converted.Blohm & Voss BV 138 MStri-motor flying boats were also used for this purpose.

TheMH-53E Sea Dragonhelicopter is used primarily by theUnited States Navyto tow several types of mine hunting or mine sweeping gear through the water. It replaced the earlier, RH-53A and RH-53D variants of theSikorsky CH-53 Sea Stallion.Other examples of minesweeping helicopters include the RH-3A variant of theSikorsky SH-3 Sea King,as well as the Mi-14BT variant of theMil Mi-14and the MCH-101 variant of theAgustaWestland AW101.

See also

• Minehunter

External links

• Dewar, Alfred (1922)."Minesweeping and Minelaying".Encyclopædia Britannica.Vol. 31 (12th ed.). pp. 949–995.