Notes

Mines can be laid in many ways: by purpose-built mine layers, refitted ships, submarines, or aircraft—and even by dropping them into a harbor by hand. They can be inexpensive: some variants can cost as little as
US$2000, though more sophisticated mines can cost millions of dollars, be equipped with several kinds of sensors, and deliver a warhead by rocket or torpedo.

British Mk 14 sea mine
Their flexibility and cost-effectiveness make mines attractive to the less powerful belligerent in asymmetric warfare. The cost of producing and laying a mine is usually anywhere from 0.5% to 10% of the cost of removing it, and it can take up to 200 times as long to clear a minefield as to lay it. Parts of some World War II naval minefields still exist because they are too extensive and expensive to clear.[1] It is possible for some of these 1940s-era mines to remain dangerous for many years to come.

Mines have been employed as offensive or defensive weapons in rivers, lakes, estuaries, seas, and oceans, but they can also be used as tools of psychological warfare. Offensive mines are placed in enemy waters, outside harbours and across important shipping routes with the aim of sinking both merchant and military vessels. Defensive minefields safeguard key stretches of coast from enemy ships and submarines, forcing them into more easily defended areas, or keeping them away from sensitive ones.

Minefields designed for psychological effect are usually placed on trade routes and are used to stop shipping from reaching an enemy nation. They are often spread thinly, to create an impression of minefields existing across large areas. A single mine inserted strategically on a shipping route can stop maritime movements for days while the entire area is swept.

International law requires nations to declare when they mine an area, to make it easier for civil shipping to avoid the mines. The warnings do not have to be specific; for example, during World War II, Britain declared simply that it had mined the English Channel, North Sea, and French coast.

History
Early use

A 14th-century drawn illustration of a naval mine and page description from the Huolongjing
Precursors to naval mines were first invented by Han Chinese innovators of Imperial China and were described in thorough detail by the early Ming dynasty artillery officer Jiao Yu, in his 14th century military treatise known as the Huolongjing.[2] Chinese records tell of naval explosives in the 16th century, used to fight against Japanese pirates (wokou). This kind of naval mine was loaded in a wooden box, sealed with putty. General Qi Jiguang made several timed, drifting explosives, to harass Japanese pirate ships.[3] The Tiangong Kaiwu (The Exploitation of the Works of Nature) treatise, written by Song Yingxing in 1637 AD, describes naval mines with a rip cord pulled by hidden ambushers located on the nearby shore who rotated a steel wheellock flint mechanism to produce sparks and ignite the fuse of the naval mine.[4] Although this is the rotating steel wheellock's first use in naval mines, Jiao Yu had described their use for land mines back in the 14th century.[5]

The first plan for a sea mine in the West was by Ralph Rabbards, who presented his design to Queen Elizabeth I of England in 1574.[4] The Dutch inventor Cornelius Drebbel was employed in the Office of Ordnance by King Charles I of England to make weapons, including a "floating petard" which proved a failure.[6] Weapons of this type were apparently tried by the English at the Siege of La Rochelle in 1627.[7]


David Bushnell's mines destroying a British ship in 1777
American David Bushnell developed the first American naval mine for use against the British in the American War of Independence.[8] It was a watertight keg filled with gunpowder that was floated toward the enemy, detonated by a sparking mechanism if it struck a ship. It was used on the Delaware River as a drift mine.[9]