Minesweeping is the practice of the removal of explosive
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 by
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. 
Minesweepers protect themselves with an
The distance sweep mimics the sound and magnetism of a ship and is pulled behind the sweeper. It has floating coils and large underwater drums. It is the only sweep effective against bottom mines.
Modern influence mines are designed to discriminate against false inputs and are therefore much harder 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 in order 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 mine
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.