Minesweeping

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 the Battle of Gallipoli in 1915, when mobile howitzer batteries prevented the British and French from clearing a path through minefields.

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.

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.

To further complicate matters, influence mines may be programmed to arm themselves (or disarm automatically—known as self-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.

During the Second World War, fifteen British Vickers Wellington bombers were modified to carry a large magnetic induction loop and an electrical 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 the Dutch royal family to the UK.