Mine Warfare at Sea

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By Rear Admiral Chris Bennet south African Navy (retired)

Published in African Security Review Vol 7 No 5, 1998

"Mines are the least appreciated of naval weapons. Their use is often seen as an unwelcome and rather passive and ‘defensive’ alternative to more ‘normal’ types of naval warfare."¹

Although mine warfare at sea is an extremely important aspect of naval capabilities, it is one that tends to be at best neglected and at worst ignored by many navies. It is interesting to note, for example, that the mighty United States Navy, although it had an extremely comprehensive and effective mine countermeasures force at the end of World War II, suffered tremendous losses a mere five years later during the Korean War due to the virtual total loss of this capability in that short time.

The low interest in and neglect of mine warfare can probably be ascribed to its not being seen as one of the ‘glamourous’ or ‘high profile’ functions of a navy; these are more likely to be submarines or surface combatants. In addition, there is never any direct contact with an enemy in mine warfare, since the mine is laid and then left to detonate or not on its own. In fact, the mine layer goes out of his way to avoid any contact with an enemy during the whole process and is far away before the mines he has laid become active.

At the opposite end of the spectrum of mine warfare, mine counter-measures tend to be even less glamourous. Although clearing mines is a very dangerous task, it is usually drawn out, arduous and boring. Again, even when a mine is detected or swept there is still no contact with an enemy.

Notwithstanding this low interest, "[m]ines have accounted for more US Navy ship casualties than any other single source since the end of World War II."² Fourteen ships have been lost to mines versus four from other causes. All navies should be aware of the risks mines pose to their fleets and ensure that they develop and maintain a mine warfare capability. From time to time in the world’s bigger navies, a situation occurs which serves to remind planners to include mine warfare in their planning. In Britain, for example, the Royal Navy, "which began a large fleet of MCM vessels in the 1950s but then rather lost interest as strategies changed and alternative, more spectacular priorities were preferred", once again changed course in the late 1980s and by 1990 was "investing over a billion pounds in efforts to improve its MCM potential."³

"A mine is an explosive device laid in water, on the seabed or in the subsoil thereof, with the intention of damaging or sinking ships or of deterring ships from entering the area."⁴

The sea-mine differs considerably from the landmine, both in its form and use. In contrast to the landmine, the sea-mine, even in its smallest form, is relatively large, heavy, complex and expensive. Additionally, a sea-mine is used as a strategic rather than 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 in war from as far back as the 16th century, when 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 extent that the development and use of the ‘Automatic Submarine Contact Mine’ at the turn of the century, 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 remained static where they were laid and floated 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 actual 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 achieve an effective one.

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 of these, of a passing vessel. By the end of this war, the ‘contact’ mine had largely 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 Persian Gulf wars of the 1980s.

Early influence mines used only the acoustic signature of the passing vessel and, due to differences and variations in acoustic signatures of ships, tended to detonate at some distance from the target vessel. In order to make them more effective, magnetic and pressure sensors were developed to be used, usually in combination with each other and/or the acoustic sensor, rather than individually.

To achieve its objective of sinking or damaging a ship passing near or over it, a ground-mine requires a large warhead — usually in the order of at least 200 kilograms of explosives — as well as increasingly sophisticated and complex electronic systems. It is these two requirements which make the modern sea-mine not only heavy and bulky, but also electronically complex and therefore expensive in relative terms to develop and produce.

In order to improve their operational characteristics and to counteract developments in mine countermeasures, the modern sea-mine is usually activated by the passing target’s magnetic, acoustic, or pressure signature, or any combination of two or all three of these signatures. It is capable of being programmed to fulfil any one, or a combination of the following functions:

select a specific ship, or type of ship by its signature before activation;



become fully active only after a specific number of vessels of specific signature type have passed within its detection range;



remain dormant and only activate after a set time has passed after laying or when instructed by a coded sound signal; or



deactivate after a set time interval, or when instructed to do so by a coded sound signal.

Although some navies keep specially designed or converted mine-laying ships, sea-mines may also "be laid by a wide variety of platforms: aircraft and submarines as well as surface ships of all shapes and sizes. Covert use by unofficial groups as well as by governments has taken place and may well occur again."⁵ Notwithstanding this factor and due to the complexity of sea-mines, as well as their use as a strategic rather than a tactical weapon, mine warfare at sea requires detailed preplanning for effective utilisation.

Finally, ground-mines are generally only effective in relatively shallow waters and, although moored mines can be used in deeper waters, they tend to encounter problems with currents and high swell conditions. Their major use is therefore limited almost exclusively to coastal or territorial waters.

The only international convention on the use of sea-mines is The Hague Convention VIII of 1907, which applied to the one type of mine in use at the time, known as an ‘automatic contact mine,’ a free-floating, or moored, buoyant contact mine. The Convention made no real provision for future technological development in mine warfare and, in the passing years, the sea-mine has developed beyond the concept of those who formulated the Convention. Although Howard S Levie states that a "new convention on mine warfare is long overdue", he concludes that "the likelihood of such a convention being drafted and becoming effective appears to be remote."⁶ In his notes on this chapter, he makes the following interesting comment on this statement: "One valid reason for the reluctance of the major maritime powers to embark on any such enterprise, much as they might favour additional regulations governing the use of mines, is that, as has happened in parallel situations in the not too distant past, a combination of States with no navies to speak of, some completely landlocked, and with little or no experience in this field, could, and undoubtedly would, dictate what the regulations should be — resulting in a convention which the maritime States would refuse to ratify, thus creating an even more confused status than that which now exists."⁷

Notwithstanding the above comment, much of The Hague Convention VIII, if read in conjunction 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 of international lawyers and naval experts on the need for modernisation of the laws applicable to the conduct of armed conflict at sea. The result of these meetings was published in 1994 under the title 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 by using the basis of customary law, as well as Protocol II of the Conventional Weapons Convention (1980) regarding prohibitions and restrictions on mine warfare on land. From this process, reasonably concise and clear rules regarding mine warfare at sea were developed, which also form a framework from which much of the strategic implications of mine warfare at sea may be derived.⁸

Even though these ‘rules’ do not have the full authority of a ratified international convention, they do express many of the generally accepted standards applied by most maritime nations in the execution of mine warfare at sea. By dividing the thirteen applicable paragraphs of the San Remo Manual (numbers 80 to 92) into three groups, they express, firstly, the military strategic requirements of mine warfare (paragraphs 80 to 84), secondly, the protection of the rights of non-belligerent and neutral states shipping (paragraphs 85 to 89), and lastly, the responsibilities of both belligerent and neutral states in regard to the clearing of mine fields (paragraphs 90 to 92).

Generally accepted military doctrine throughout the world usually agrees that the target of the sea-mine is a ship (usually warships or merchant vessels carrying ‘war’ cargoes), and not the people on those ships or the general public. It distinguishes between three forms of mine warfare at sea, all of which emphasise the fact that indiscriminate mining is considered unlawful:

defensive mining: the use of minefields to deny access by the enemy to the territory of the defender;



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 or roadstead under the control of an enemy state, to deny that enemy and its allies the use of their essential maritime lines of communication.

The first five paragraphs (80 to 84) of the San Remo Manual provide a logical framework for the formulation of general maritime military strategic principles for the utilisation of sea-mines:

"80. Mines may only be used for legitimate military purposes including the denial of sea areas to the enemy.8I. Without prejudice to the rules set out in paragraph 82, the parties to the conflict shall not lay mines unless effective neutralisation occurs when they have become detached or control over them is otherwise lost.

82. It is forbidden to use free-floating mines unless: (a) they are directed against a military target, and (b) they become harmless within an hour after loss of control over them.

83. The laying of armed mines or the arming of prelaid mines must be notified unless the mines can only detonate against ships which are military objectives.

84. Belligerents shall record the locations where they have laid mines."

These paragraphs set the military strategic tone by specifying that sea-mines may only be used for legitimate military purposes, and highlighting their primary use as the denial of sea areas to an enemy. According to Eric Grove, "[s]till perhaps the most effective means of closing a harbour in war or violent peace is the underwater explosive device set to be exploded by a passing ship."⁹ This implies further that "[t]hese unspectacular weapons look like retaining a considerable degree of effectiveness for sea denial for many years to come."¹⁰

These paragraphs also specify certain controls, such as the limited duration of any ‘free-floating’ mine (which, of course, can also be extended to include a torpedo which misses its target and reaches the limit of its fuel), the need to notify all shipping (including both neutrals and belligerents) of the fact that a minefield has been laid, and the requirement to record the positions of all mines laid. All these aspects form the foundation on which conventional strategic mine warfare is formulated.

Unfortunately, as stated earlier, the effectiveness of mine warfare at sea is often lost in the aftermath of more glamourous exploits. For example, studies of the Pacific campaigns of World War II demonstrate the probability that, if Operation Starvation, a mine-laying operation in the Pacific in 1945 designed to do exactly that (starve Japan) had "been commenced some months earlier, it could have reduced Japanese resistance on Okinawa and may have caused a Japanese surrender without the need to drop the atomic bombs on Hiroshima and Nagasaki."¹¹

Mines should therefore be considered and utilised 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 target vessel, the effectiveness or otherwise of a minefield should not be decided by the actual quantity of ships that are sunk or damaged by mines, but rather by whether or not the enemy stays out of the area of denial. To an extent, it can be said that a totally effective minefield is one in which no ships were sunk because no unwanted ships had the temerity to attempt passage through the declared field. In this context, the mining of North Vietnamese waters in 1972 is a good example. Although not one ocean-going vessel was sunk, the blockade was considered to be completely effective.¹²

The question that arises is whether the mere fact of the existence of a minefield — or, for that matter, even an unsubstantiated statement of such existence — will deny enemy ships access to these waters. In this sense, it is obvious that, if a state is known to have both the capability and the will to lay effective minefields, the mere statement that a field has been established (i.e. disinformation) could be sufficient reason for ships not to enter that area. As can be seen, 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 in both peace and war, to follow the mandatory requirement of notification of dangers, both natural and man-made, to peaceful shipping. In most cases, this is achieved by a system of written and/or radioed Notices to Mariners, available to all mariners and to the International Maritime Organisation, that is used to notify all shipping (naval or merchant, belligerent or neutral) of any short term dangers to navigation or changes which do not appear on previously issued navigational charts. The notification regarding the establishment or clearing of a minefield would thus be part of this normal process of ensuring navigational safety at sea.

The need to record the locations where mines have been laid, requires not merely that the ‘general area’ of a minefield is recorded, but that an accurate record of the position of each and every mine is kept. This is both more feasible and easier to implement with modern navigation systems such as the Global Positioning System, and has a large degree of ‘self-interest’ in its execution in that it:

is a means of ensuring the protection of own and friendly vessels entering areas of conflict, either during or after the conclusion of that conflict;



simplifies the task of safely ‘refilling’ the minefield, i.e. replacing detonated mines; and



considerably eases the requirement to provide for the removal or neutralisation of mines at the cessation of hostilities.

It is these last areas of self-interest which demand that any nation, in the process of developing and manufacturing sea-mines, must also have a mine-clearance capability, specifically to clear or render harmless any mine that it develops and/or manufactures itself.

The next five paragraphs (85 to 89) of the San Remo Manual express the requirement to provide for the protection of shipping from nations not involved in a conflict, during the period of conflict:

"85. Mining operations in the internal waters, territorial waters, territorial sea or archipelago waters of a belligerent State should provide, when the mining is first executed, for free exit of shipping of neutral States.

86. Mining of neutral waters by a belligerent is prohibited.

87. Mining shall not have the practical effect of preventing passage between neutral waters and international waters.

88. The mine laying States shall pay due regard to the legitimate uses of the high seas by, inter alia, providing safe alternative routes for shipping of neutral States.

89. Transit passage through international straights [sic] and passage through waters subject to the right of archipelagic sea lanes passage shall not be impeded unless safe and convenient alternative routes are provided."

These five recommendations require the strategic planners to ensure that they do not encroach upon the waters of neutral states, that they allow shipping to exit freely and safely from any area of hostilities, and that they do not hamper the normal flow of maritime trade.

Of particular interest here is the definition of ‘neutral waters’ as given in the San Remo Manual: "Neutral waters consist of the internal waters, territorial sea, and, where applicable, the archipelagic waters, of neutral States. Neutral airspace consists of the airspace over neutral waters and the land territory of neutral States."¹³

This can be interpreted to mean that, where a neutral maritime state finds itself between two belligerent maritime states, for example, it is only in territorial waters — extending to a maximum of twelve nautical miles from the coast — that the belligerents may not lay mines in terms of international law. The only limitation is the need to provide 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 transit through the Straits of Gibraltar and offering the route through the Suez Canal and around the Cape of Good Hope as an alternative. Consideration must also be given to the fact that alternative routes are also 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 safely through the minefield by using cleared channels.

The last section (paragraphs 90 to 92) of the San Remo Manual express the responsibilities of belligerent states with regard to the clearance of mines that they have laid and the rights of neutral states to clear mines that hamper their shipping:

"90. After the cessation of active hostilities, parties to the conflict shall do their utmost to remove or render harmless the mines they have laid, each party removing its own mines. With regard to mines laid in the territorial waters of the enemy, each party shall notify the position and proceed with the least possible delay to remove the mines in its territorial sea or otherwise render the territorial sea safe for navigation.

91. In addition to their obligations under paragraph 90, parties to the conflict shall endeavour to reach agreement, both amongst themselves and, where appropriate with other States and with international organisations, on the provision of information and technical material assistance, including in appropriate circumstances joint operations, necessary to remove minefields or otherwise render them harmless.

92. Neutral States do not commit an act inconsistent with the laws of neutrality by clearing mines laid in violation of international law."

The obligations in paragraphs 90 and 91 are very closely linked and 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 are also without prejudice to international law on 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 a country’s own vessels and for the requirement of neutralisation at the close of hostilities. By convention, most, if not all, modem sea-mines have some form of automatic ‘disarming’ or ‘neutralising’ mechanism to make them inactive after they have served their strategic purpose.

The use of the phrase "and with international organisations" recognises the growth of non-governmental organisations in the clearance of landmines, and while such organisations do not necessarily exist for sea-mines at present, such a possibility should not be excluded in the future. Non-governmental organisations which have gained expertise in this field, should be used as a complementary 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 towards the shipping of all belligerents and prohibiting it from taking any active measure which may affect the end result of any conflict between other states.

Mine warfare remains an important tool of modern navies, and in its conventional use by recognised 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 a conflict by controlling access to or through waterways, makes it a powerful option. However, as in the laying of any form of automatic mine, 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, firstly, that it keeps an accurate record of where each mine is laid. Secondly, such a country or group is responsible for the development and maintenance of the ability to clear or disarm any mines in its inventory.