The sea mine differs considerably from the land mine. In contrast to the land mine, the sea mine can vary greatly in size, but is usually relatively large, heavy, complex, and expensive. In addition, a sea mine is used as a strategic rather than as a tactical weapon. Until the modern self-propelled torpedo was developed, the sea mine was known as a torpedo and had a long history of use. As far back as the 16th century, an Italian engineer working for the Dutch floated explosives down the Scheldt River in an attempt to blow up a bridge. "Torpedoes"—or sea mines—were used extensively in the various wars of the 19th century, to the point that at the turn of the century the development and use of the "automatic submarine contact mine" resulted in the Hague Convention VIII of 1907 (ratified in 1910).
Early sea mines were buoyant, and initially floated just below the surface of the water—moving with tides and currents. Later developments caused them to be moored so that they floated just below the surface at a depth conducive to being detonated when the target vessel's hull made direct contact with the mine. The requirement to make contact with the target meant that the "buoyant contact mine" had an extremely small initiation radius (effectively its own diameter), and as a result large numbers of mines were required in these early minefields in order to be effective.
World War II saw the development of the influence mine, mainly in the form of a negatively buoyant ground mine requiring complex sensors and control circuits. It lies on the seabed and is activated by the sound. magnetic, or pressure signature (or any combination thereof) of a passing vessel. By the end of the war the contact mine largely had been overtaken by this new form of mine, and in the years since most, if not all, development work on sea mines has been aimed at the ground mine. Quantities of the older moored mines still exist, however, and were used in the Iran-Iraq War and the Gulf War.
Many modern ground mines have large warheads (upwards of 200 kg) and are consequently heavy and bulky—but there are also many mines which are quite small and difficult to detect. In order to improve their operational characteristics and to counteract developments in mine countermeasures, the modern sea mine usually is activated by the passing target's magnetic, acoustic, or pressure signature. It is capable of being programmed to fulfill any one, or a combination of the following functions: (a) select a specific ship, or type of ship, by its signature before activation; (b) become fully active only after a specific number of vessels of a specific signature type have passed within its detection range; (c) remain dormant and only activate after a set time has passed, or when instructed to by a coded sound signal: or (d) deactivate after a set time interval, or when instructed to by a coded sound signal. Though rising mines can be laid in very deep water, their still limited use outside the former Soviet Union means that most modern mines present the greatest danger in coastal and territorial waters.
Although some navies keep specially designed or converted mine-laying ships, sea mines may also be laid by a wide array of platforms: aircraft, submarines, as well as surface ships. Covert use by non-governmental organizations or groups has also taken place. Notwithstanding this factor, the complexity of sea mines and their primary use as a strategic rather than as a tactical weapon demand that mine warfare at sea required detailed preplanning for effective use.
International Rules of Mine Usage
At the time of the Hague Convention in 1907, there was only one type of mine in use at that time—known as an "automatic contact mine"—a free floating, or moored, buoyant contact mine. This convention made no provision for future technological development in mine warfare. and in the years since the sea mine has developed beyond the concept of those who formulated the convention. Although Howard S. Levie, in his book Mine Warfare At Sea , states that a "new convention on mine warfare is long overdue," he believes that "the likelihood of such a convention being drafted and becoming effective appears to be remote."
Much of the Hague Convention, if read in combination with other international conventions, is still applicable today. This has been demonstrated by an initiative of the International Institute of Humanitarian Law in 1987, which held a series of meetings among international lawyers and naval experts on the need for modernization of the laws applicable to the war at sea. The result of these meetings was published in 1994 under the title of San Remo Manual on International Law Applicable to Armed Conflicts at Sea . Apart from other aspects of naval warfare, this manual also covers mine warfare at sea and builds on the Hague Convention using customary law as a basis as well as Protocol II of the Conventional Weapons Convention of 1980 regarding prohibitions and restrictions on mine warfare on land. From these documents reasonably concise and clear rules regarding mine warfare at sea were developed.
These rules express many of the generally accepted standards applied by most maritime nations in the execution of mine warfare at sea. The relevant paragraphs of the San Remo Manual (numbers 80 to 92) are divided into three groups: the military strategic requirements of mine warfare (paragraphs 80 to 84); the protection of the rights of non-belligerent and neutral states' shipping (paragraphs 85 to 89); and the responsibilities of both belligerent and neutral states in regard to the clearing of mine fields (paragraphs 90 to 92).
Military Strategic Requirements
Generally accepted military doctrine throughout the world recognizes that the target of the sea mine is a ship and not the people in those ships or the general public. It distinguishes between three forms of mine warfare at sea, all of which emphasize the fact that indiscriminate mining is considered unlawful: defensive mining—the use of minefields to deny access by the enemy to the defender's territory; protective mining—the use of minefields to protect shipping routes by denying enemy submarines or surface craft the use of certain waters outside the coastal waters of the defender; and offensive mining—the use of minefields in waters under the control of an enemy state.
The first five paragraphs of the San Remo Manual set the military strategic tone by specifying that sea mines may only be used for legitimate military purposes, and highlight their primary use for the denial of sea areas to an enemy. These paragraphs also specify certain controls, such as limiting the duration of any "free floating" mine (by forbidding the laying of a mine if it does not neutralize or deactivate itself when it is detached), the need to notify all shipping (including both neutrals and belligerents) of the fact that a mine field has been laid, and the requirement to record the positions of all mines laid.
Unfortunately, the effectiveness of mine warfare at sea is often lost in the aftermath of more "glamorous" exploits. For example, studies of the Pacific campaigns of World War II suggest the probability that if Operation Starvation (a mine laying operation begun in March 1945, designed to do exactly that—starve Japan) had been commenced earlier than it was, Japanese resistance might have ceased without the need to drop the atomic bombs on Hiroshima and Nagasaki.
Mines should therefore be considered and employed as a means to deny an enemy the use of certain sea areas, a use which introduces the strategic planner to a seeming contradiction in terms: although an individual mine is designed to sink a vessel, the effectiveness of a minefield is not decided by the actual number of ships sunk or damaged by mines—but rather by whether or not the enemy stays out of the area of denial. A totally effective minefield can be one where no ships are sunk, because no unwanted ships had the temerity to attempt passage through the declared field. The mining of North Vietnamese waters in 1972 is a good example. Although not one oceangoing vessel was sunk, the blockade was considered 100% effective. In addition, if a state is known to have both the capability and the will to lay effective minefields, the mere suggestion that a field has been established (i.e., disinformation) could be sufficient reason for ships not to enter that area. Mine warfare at sea is not only an effective weapon in a direct sense, but is also an extremely effective form of psychological deterrence.
It is normal practice in most maritime nations during both peace and war to follow the mandatory requirement of notification of dangers, both natural and manmade, to peaceful shipping. In most cases this is achieved by a system of written and/or radioed Notices to Mariners, available to all merchantmen and to the International Maritime Organization. The notification regarding the establishment or clearing of a minefield would thus be part of this process of ensuring navigational safety at sea. The need to record the locations where mines have been laid requires not only that the general area of a minefield be recorded, but that an accurate position of each and every mine be kept. This is both more feasible and easier to implement with modern accurate navigation systems such as the Global Positioning System, and has a large degree of self-interest in that it ensures the safety of friendly shipping and simplifies the task of removing or altering the minefield.
Protection of Non-Belligerent Shipping
The next five paragraphs (85 to 89) of the San Remo Manual express the requirement to provide for protection of shipping from nations not involved in a conflict. The five recommendations outlined in this section require strategic planners to ensure the exit of neutral shipping from a belligerent's waters, that a belligerent not encroach on the waters of neutral states, that they allow neutral shipping to enter international waters, that neutrals be given access to alternate shipping routes, and that international straits not be impeded unless a convenient alternative route is provided.
Of particular interest is the definition given of "neutral waters:" the internal waters, territorial seas, and archipelagic waters of neutral states. This can be interpreted to mean, for example, that when a neutral maritime state finds itself between two belligerent maritime states, it is only in territorial water—extending to a maximum of 12 nautical miles from the coast—that the belligerents may not lay mines. The only limitation is the need to provide for a safe route for shipping entering or leaving neutral waters.
In the provision of safe alternative routes, the word "convenient" rules out those cases in which either no alternative, or only an alternative with unacceptable commercial consequences, is offered by belligerents. An extreme example of the latter would be the impeding of passage through the Strait of Gibraltar and offering the route through Suez and round the Cape of Good Hope as an alternative. Consideration also must be given to the fact that alternative routes are merely one of the ways in which belligerents may choose to protect peaceful shipping. Another effective way, for example, would be the provision of escort services allowing neutral and/or friendly shipping to sail in safety through the minefield unharmed using cleared channels.
Mine Clearance Rights and Responsibilities
The last section of the San Remo Manual deals with the responsibilities of belligerent states in regard to the clearance of mines that they have laid, and the rights of neutral states to clear mines hampering their shipping. The obligations in paragraph 90—that after hostilities the parties do their best to remove their own minefields—and in paragraph 91—that former combatants discuss with each other and with international organizations how to remove their mines-are very closely linked. They contrast sharply with the lesser obligations in its counterpart in land warfare found in Protocol II of the Conventional Weapons Convention adopted in 1980. These rules also are without prejudice to international law with regard to state responsibility. As a result, the use of sea mines is usually controlled and the position of each mine laid is normally recorded, both for the safety of friendly vessels and for the requirement of neutralization. Most, if not all, modern sea mines have some form of automatic disarming or neutralizing mechanism to make them inactive after they have served their purpose.
The reference to international organizations recognizes the growth of nongovernmental organizations in the clearance of land mines, and while such organizations do not necessarily exist for sea mines at present, such a possibility should not be excluded in the future. Non-governmental organizations which have gained expertise in this field should be used as a complimentary resource when it becomes beneficial to the protection of international shipping.
Paragraph 92 expresses the right of a neutral state to take active measures to protect and clear its shipping routes within its own waters, without in any way affecting its position of neutrality. To an extent, this right is an exception to the traditional rules requiring a neutral maritime state to act with complete impartiality toward the shipping of all belligerents, and prohibiting it from taking active measures that may affect the end result of conflicts between other states.
Mine warfare remains an important tool of modern navies, and in its conventional use by recognized maritime states, has not developed beyond the existing regulations and conventions prohibiting unlawful use. Its utility, alone or in combination with other measures, to determine the course of conflict by controlling access to or through waterways makes it a powerful option. However, when any form of automatic mine is laid—whether on land or in the sea—accepted international law clearly states that it is the responsibility of the country or group laying a minefield to ensure that it keeps an accurate record of where each mine is laid. Such a country or group also is responsible for the development and maintenance of the ability to clear or disarm any mines in its inventory.
Rear Admiral Bennett is a research associate with the South African Institute for Security Studies.