The brief historical résumé of the history of the development and use of naval mines contained herein is taken from a “Study of the Mission of the Mine Squadron,” which was prepared by Lieutenant Commander Bagby during the time that he was mining officer of the mining squadron of the scouting fleet. Necessarily, the confidential matter has been eliminated, but the article is otherwise practically unchanged.
C. H. Wright,
Lieutenant Commander, U.S.N.
There are two general classes of mines which need to be defined before reaching a proper conception of the scope of naval mining as distinguished from coast defense mining, which, in the United States, is under the direction of the War Department. In coast defense mining the Army uses a controlled mine; that is, a mine whose firing circuit is led to some control station on shore so that the mine cannot fire until an observer on shore completes the firing circuit. The controlled mine must, necessarily, be fixed to the bottom and must be placed in shoal water near a shore which is commanded by our own forces. The controlled mine then denies an area to the enemy but offers no menace to friendly ships.
Naval mining, on the other hand, uses a contact mine, that is, a mine whose firing circuit is complete within the mine itself so that the mine will fire when the presence of any ship in its danger area operates the firing mechanism. The contact mine denies the same area to friendly ships as to the enemy. It may be a ground mine resting on the bottom, a moored mine attached to its anchor by means of a cable, or a drifting mine with no connection to the bottom. The ground mine must, of course, be laid in shoal water; the moored mine may be laid in any water where the depth is less than five hundred fathoms; the drifting mine may be laid in any water available to the mine-laying vessel. A description of these types of mines will be given later.
A controlled mine is a purely defensive weapon, while the contact mine may be used in a larger field either offensively or defensively.
From the first use of the mine, in 1585, when vessels loaded with explosives and fired by clockwork destroyed a bridge in the Scheldt River, until the Russo-Japanese War in 1904, it appears that all nations regarded the mine as a purely defensive weapon, much in the nature of a fixed fortification for the protection of their own ports or harbors, or for denying the enemy access to any waters which were under their own control. This conception, or rather this limited use of mines, left only a very small field for naval mining. That this conception persisted in our own service even after the Russo-Japanese War is shown by the following quotations. They are taken from a letter and its endorsements which caused the decision to remove mines from our battleships about 1910.
The mine is a purely defensive weapon.
The occasion for which particular provision should be made in use of mines in the Navy is in connection with advanced base work.
It appears that mines now carried in battleships and armored cruisers would rarely be used except for the fortification of an advanced base and the mines required for such purpose would better be included in the advanced base material handled by a special organization and carried in a special ship.
The opinion given in these quotations would limit the use of mines to pure defense and would limit the use of such mines as may be laid by the Navy to the fortification of an advanced base. In a lecture delivered at our Naval, War College in 1911, however, it was stated:
Now as a matter of fact, advanced base mining has nothing whatever in common with the mining which will be required by the Navy. A different mine is required for the two purposes and the mine ship is not fitted for laying the type of mine which is best adapted for advanced base work.
The first war which employed naval mining in a larger field was the Russo-Japanese War. During this war, contact mines were extensively used by both the belligerents. The only strictly defensive mine laying was done by the Russians in the bays around Port Arthur to prevent the landing of the Japanese Army, and in the entrance to Port Arthur to put a stop to Japanese blocking operations. The first casualty was the sinking of two Russian ships by their own hastily placed contact mines. They then delayed the mining of the entrance to Port Arthur until controlled mines could be received from Russia. In this connection, an official booklet published in 1920 entitled Joint Army and Navy Action in Coast Defense, states:
In general, however, it must be realized that the laying of mines in our waters is a dangerous procedure because our vessels may enter the mine field through carelessness or some mistake or neglect in disseminating information. Mines may also break adrift and become dangerous to our vessels.
Moored contact mines were laid offensively during the Russo-Japanese War for the following purposes:
- By the Japanese to bottle up the Russians in Port Arthur. This mining was only partially successful as the Russian mine sweepers were able to keep a clear channel. The mine did, however, delay and hamper the movements of the Russians.
- By both belligerents in laying mines surreptitiously on the known cruising grounds of the enemy. This form of mining was eminently successful. The mines were laid during the darkness or fog, the Japanese using destroyers and small converted steamers, the Russians using regular mine layers and destroyers. One Russian and two Japanese battleships were sunk by this form of mining.
This mining may be regarded as the primary step in the offensive tactics of mining, a form of tactics which was certain to develop in the next war.
The Russo-Japanese War gave only one example of the use of drifting mines. In the battle of August 10, while the Japanese were forming their line, Japanese destroyers were sent ahead of the Russian line. There is some question whether the destroyers actually laid mines, although there is no doubt that they were able to do so. An eye witness reported having seen two drifting mines. The Russian admiral made signal: “Attention—drifting mines,” and changed the course of the Russian fleet by four points. Whether the Japanese destroyers actually laid mines is not important; it is important that the Russian admiral was forced, by fear of mines, to change his course.
The following table shows the number of vessels stink by mines in the Russo-Japanese War:
After the Russo-Japanese War, all the principal naval powers, except the United States, gave great attention to the development of mines, mine vessels, and mining organization, and included the use of mines in their strategical and tactical exercises. Great Britain, Japan, and Italy turned all mining over to the navy. Austria fitted all naval vessels with mine-laying installations. England abandoned harbor defense mining entirely. From these preparations, it is easily assumed that all nations which gave mining serious thought and study, fully expected that the offensive use of mines introduced in the Russo-Japanese War would be a feature of the next naval war.
Prior to the World War, it was the intention of Germany to mine the English ports immediately on the outbreak of war for the purpose of delaying the mobilization of the British fleet. This excellent plan was frustrated by the mobilization of the British fleet before war was declared. From the beginning, and throughout the war Germany vigorously pursued a campaign of mine laying along the English coast. For this mine laying she used moored contact mines laid by submarines. Occasional drifting mines were also found. This campaign forced England to adopt practically continuous mine sweeping to keep her ports open.
To supplement the mining of English ports, the Germans also laid moored mines in the vicinity of lightships, buoys, or other navigational marks; and, in fact, at any place where they expected either men-of-war or merchant vessels might cruise or pass. This caused the North Sea to be more or less strewn with mines on the chance that some of them might be effective.
The Germans laid extensive fields in the Baltic and along the eastern shores of the North Sea. These mine fields did no actual damage to the British fleet; on the contrary they were a constant menace to the Germans themselves. One German cruiser is known to have been sunk by these mines. The fields were laid probably in order to give protection to a retiring German fleet, and the known existence of the fields did influence the tactics of the British fleet, particularly in forcing the British battle cruisers in the Dogger Bank action to give up the chase and to countermarch when within fifty miles of Heligoland. This is an example of the tactical use of moored mines for covering a retreat to a base; had the existence of the fields not been known to the British it might have been an example of luring an enemy over mine fields.
At the beginning of the war, England lost valuable time by not having an efficient mine and mining organization ready for immediate employment. Subsequently, British mines were laid in the Skaggerack and Cattegat and along the eastern shores of the North Sea in order to block the areas and channels which the Germans had left for themselves. This caused the Germans, in turn, to adopt continuous mine sweeping to keep their North Sea bases open.
Both England and Germany used moored contact mines defensively in the protection of their naval bases. The British trusted more to boom and net defenses, but placed mines in the nets. In this defensive mining the controlled mine does not appear to have been used. The Germans, using contact mines, mined themselves in so thoroughly at Wilhelmshaven that they were unable to use that port as an operating base. The novel reason given by them was that the British had also mined themselves in and there was no further prospect of an engagement between the fleets.
The biggest mining operation of the war was the closing of the North Sea by a British field at Dover and a combined British-American system of fields extending from the Orkneys to Norway, known as the Northern Barrage. The object of these fields was to confine German submarines to the North Sea. The fields were laid during 1918. The Northern Barrage was not completed when the armistice was signed; consequently the full effectiveness was never demonstrated. Of the effect of the Northern Barrage, Admiral Strauss stated:
With the information at present available, it appears that a total of six submarines were destroyed in the barrage and possibly an equal number were severely damaged.
In the other theaters of the naval war, mines were used for practically the same purposes stated heretofore, with one exception. During the Gallipoli campaign the Turks took advantage of the current in the Dardanelles to launch drifting mines against the allied ships. These mines are known to have sunk one battleship and are credited with sinking two others. The Turks also used controlled mines with great success in connection with barbed wire entanglements to oppose the landing of the British troops on the Gallipoli peninsula.
The tactical use of the drifting mine in connection with a fleet engagement, which had been so freely predicted, did not appear. There are two probable reasons. In the first place, the North Sea, the principal scene of the naval war, is shallow, and moored mines, laid beforehand in known positions could be utilized in the place of tactical mining during the progress of an engagement. In the second place, the waters of the North Sea are so restricted, and were already so well mined, that each side felt that further tactical mining would offer probably as great a menace to itself as to the enemy. It was reported that the Germans, in their raids against English coast towns, carried mines with them in hope of sinking pursuers, but otherwise it does not appear that mines or mine layers were carried with either fleet.
Due to the character of the World War, merchant vessels were probably the greatest sufferers from mines, but that mines also sank a considerable number of men-of-war is shown by the following table of vessels known to have been sunk by enemy mines:
From this brief history it may be seen how the use of mines developed from the Russo-Japanese War to the World War. In general, mines were used for the same purposes in the two wars, but there was an enormous increase in the number of mines laid. The total laid in the Russo-Japanese War is not known but the total in the World War was approximately 204,500.
While it would, of course, be unsafe to assume that the uses to which mines have been put in the past will be neglected in the future, it would be just as unsafe to assume that new uses cannot be found, or that the conditions of future wars will be identical with the conditions of past wars. There seems to be a development of mining which conditions of future wars may make advantageous. This is the tactical use of drifting mines. So far, we have had for an example of this type of mining, only the fear of the Russians that such mines had been laid by Japanese destroyers, and the probable use of mine layers to accompany German raiding expeditions against the English coast towns.
The menace of mines to the side which lays them has undoubtedly been a powerful deterrent in the past and must be carefully considered for the future.
This kind of mining divides itself into two classes: first, when mines are laid surreptitiously with the object of damaging the enemy by the mines and throwing him into confusion; second, when mine laying is done with the knowledge of the enemy in order to influence his tactics by his fear of the mine field. In both cases, when actual mines are laid by our own fleet our tactics may be influenced to our own disadvantage. In the first case the enemy will not be harmed unless he passes directly over the mine field; therefore, it would seem that we should not lay tactical mines surreptitiously unless we are reasonably certain that the enemy will pass over the field, and that we do not require the area for our own use.
In the second case, where the mines are laid in positions known to the enemy, his tactics would be influenced by the mine field at least as much as our own. Both fleets would, for safety, assume an area much larger than that actually mined. The advantage would lie entirely in our ability to select an area more valuable to the enemy than to ourselves. Since the purpose of this mining is to influence the enemy’s tactics by his fear of the mines, the laying of real mines is not necessary provided we can make the enemy think we have laid real mines. The use of dummy mines in this case would impose no disadvantage on our own fleet and would, if the enemy is deceived, have the same effect on him as the laying of real mines.
Tactical mining would appear to be advantageous as a means of throwing an enemy cruising formation into confusion in preparation for torpedo attack; hampering deployment of an enemy; forcing tactics disadvantageous to an enemy during battle for the better effect of our own gunfire or torpedo; covering a withdrawal or retirement of our own forces; heading off an enemy in flight.
Summarizing, the uses of naval mines as indicated by past wars are:
- The defense of our own fleet anchorage and bases (moored mines)
- The closing of enemy ports (moored mines).
- The closing of passages useful to the enemy but not needed by ourselves (moored mines).
- The enclosing of enemy ships in extended sea area (moored mines).
- The use of mine fields as a barrage behind which we may retire (moored mines).
- The laying of mines in the theater of war on the enemy’s cruising ground (moored mines).
- The laying of mine fields in such position that the enemy may be lured or forced to pass over them (moored mines).
- The surreptitious laying of mines ahead of an enemy force (drifting mines).
- The laying of real or dummy mines to influence the enemy’s tactics (drifting mines).
- The launching of mines in a current against ships at anchor (drifting mines).
Types of Mines
As stated before, the dividing line in our services between mines used by the Army and those used by the Navy is established by the method of firing the mine. The army controlled mine is capable of being fired by an observer on shore, the naval contact mine carries its firing mechanism complete within the mine itself and fires when contact is made with any vessel.
The controlled mine must be fixed to the bottom in a definite known location. It may be either a ground mine, that is, the mine and its anchor remaining together in one unit resting on the bottom; or the mine itself may be buoyant and moored to its anchor by means of a cable. The choice of employment between these two types of controlled mines depends upon the depth of water and the character of bottom, and upon the method of control to be used.
Controlled mines are ordinarily placed in groups of from seven to nineteen mines. Circuits are led to shore which enable the observer to fire all groups or all mines of one group simultaneously; or to fire any particular mine of a group. There are three methods of controlling the mines:
- The observer, or observers, on shore plot the track of an enemy vessel and close the contact when the vessel is observed to be over a mine or group of mines. This method requires that the location of the mine field be visible from the control station.
- Each mine, when contact is made with a vessel, makes a signal in the control station on shore so that the observer may fire the mine. In this method, the location of the mine field need not be visible from the control station, but the observer must be informed of the location of friendly vessels.
- The firing contacts on shore may be kept closed to make the mine practically an automatic contact mine for enemy vessels; the contacts on shore being opened to permit the passage of friendly vessels. In this method, the location of the mine field need not be visible from the control station, but operator must be instructed when to open a channel for friendly vessels.
In commenting on the use of controlled mines, one of the leading authorities on mining in our Navy states:
The use of controlled mines is limited to the defense of harbor entrances and approaches in situations where suitable control points may be established within good visibility. Such mines are large and bulky and their handling is encumbered by heavy anchors and control connections. To plant a mine field of this kind is a comparatively slow operation, requiring good weather and fairly smooth sea. Hence, controlled mines are unsuitable for use on the high sea or in any mining operations involving the laying of mines in considerable number at command and in a short time. The chief value of controlled mines lies in their suitability for mining channels through which innocent or friendly traffic is to continue. Their use is only defensive, and unless adequately protected by batteries or patrol vessels, they may be swept up or their connections severed by dragging.
The naval contact mine may also be either a ground mine or a moored mine; or it may be a drifting mine, which has no connection with the bottom but floats freely on the surface or a short distance underneath the surface.
The contact mines used during the Russo-Japanese War were almost exclusively moored mines. It is not known exactly what type of anchor was employed; it was probably an automatic anchor which set the mine at a predetermined distance below the surface but did not permit mine laying except at slow speed. After the Russo-Japanese War, when the importance of mining was realized, successful efforts were made to develop an automatic anchor which would permit the mine to be laid at any speed. The result of these efforts was an automatic anchor, which first forms with the mine a buoyant unit in which no mechanism operates until outside the region of turbulent water near the rudder and propellers.
The present type of anchor is quite satisfactory, provided it functions as designed. Future developments will probably be in the direction of increased reliability. During the World War, the British at one time contemplated giving up the automatic anchor because of the danger that one anchor with faulty operation might leave a mine case on the surface and thus disclose the location of a whole field. The alternative of using an anchor with a fixed length of mooring cable with necessity of knowing beforehand the exact depth of water in which the mine is to be laid, is so disadvantageous that it will probably never come into general use.
With the advent, prior to the World War, of the submarine mine layer, the mine and anchor instead of first forming a buoyant unit were required, for submarines, to sink in order to clear the mine tube. In this type, the mine and anchor first sink to the bottom. Later, by a delay release, the mine case rises and sets the length of its mooring cable by hydrostatic pressure at the level of the mine case. There are objections to this type and it probably will not come into general use for surface mine layers.
The firing mechanisms of contact used in the World War were:
- Inertia.
- Mechanical.
- Electro-chemical.
- Electric.
The inertia firing mechanism which operates to close a circuit by the movement of an inertia ball or plunger when the mine is struck, appeared largely in the early designs of mines. It was probably used on contact mines during the Russo-Japanese War.
The mine with this firing mechanism is liable to be fired by wave action and is sensitive to countermining.
Prior to the World War, the Italian Elia mine was most popular in all navies with exception of the German and Austrian services. The Elia mine had a purely mechanical firing mechanism, operated by a horizontal firing lever pivoted around the mooring cable at its junction with the mine case. Rotation of the firing lever relatively to the mine case unlocked a bayonet joint and allowed the strain of the mooring cable to cock and trip the firing pin as the mine case was released from the mooring cable. Tests of this type of firing mechanism did not indicate reliability, only about twenty-five per cent of the mines firing on “bumping” tests. At the beginning of the World War, the British had only Elia mines but soon abandoned them. The United States issued them to naval districts in 1917, but so far as is known, none of them were ever laid. However, a type of firing mechanism which fires the mine as the mine case is rising toward the surface has distinct advantages, and may reappear in the future design.
The most widely used mine during the World War was the electro-chemical mine. In this mine, contact by a ship breaks a glass tube inside a horn projecting from the mine case. An electrolyte, usually sulphuric acid, then escapes from the tube and runs into the container of a primary cell inside the mine case. Upon receipt of this electrolyte, the primary cell generates the current to fire the detonator. This type of firing mechanism as used by the German and Austrian services was very reliable, but the British had considerable difficulity in obtaining a glass which would not break on explosion of a neighboring mine and thus allow a whole field to be countered. Their anti-submarine barrage at Dover was exploded entirely, early in 1918, by countermining.
The activities of German submarines in the World War made a strong demand for a mine to be used against subsurface craft. Contact mines prior to the war had been designed for use against surface craft and required, for firing, that a vessel make contact with the mine itself or with a firing buoy at a short distance above the mine case. The danger area of such mines was small and the number required to block a large area against submarines was prohibitive. The mine which we employed in the Northern Barrage was designed to meet the demand for larger danger area. The mine carried a vertical antenna supported by buoys, and was designed to fire on the contact of a vessel with horns on the mine case, or with any part of the antenna. The length of the antenna was from thirty-five to seventy feet, depending upon the depth at which the mine case was set and upon the destructive radius of the explosive charge at that depth. It increased the danger area of the mine in the vertical direction by several hundred per cent, and a much smaller number of mines was then required for an effective anti-submarine barrage.
During the World War, the constant use of the paravane and continuous mine sweeping operations robbed moored mines of a great deal of their effectiveness. The mine sweeping of English ports led the Germans to experiment with mines designed to defeat mine sweeping. Their first attempt was a mooring cable containing a device to permit passage of a sweep wire without cutting the mine adrift. It was not successful. The next attempt was what was called the “Monday, Tuesday, Wednesday” mine. This expressive name was given because the mine laid by submarines had a long delay on the bottom before leaving its anchor and then the mines of a field would rise on successive days. The use of this mine required vessels to be gathered in convoys and to be led in and out of port by mine sweepers.
The demand for a mine which will defeat mine sweeping is still strong. The antenna mine partially defeats the present paravane as contact of the towing wire will fire the mine as well as contact with the hull.
Another demand at the present time is a larger weight of explosive in each mine in order to increase its destructive effect. The maximum weight of high explosive carried by moored contact mines during the World War was approximately 300 pounds; and more recent underwater protection, principally on capital ships, will require a larger weight of explosive in order to have a destructive effect on capital ships at the desired radius.
One big weakness of the moored mine is its dip in a current, causing great variations in the depth of the mine. Closely allied with this weakness is the unsuitability of the ordinary moored contact mine against surface craft in places where there is a large rise and fall of tide. The mine case, in order to escape detection, and in order to do serious injury to a large ship, should not be less than fifteen feet below the surface. If the mine has a depth of fifteen feet at low slack water this depth may be increased at high water or in a strong current so that a ship of moderate draft can pass over the mine field.
The foregoing discussion has dealt primarily with the moored contact mines. The drifting contact mine, although having the same characteristics in the firing mechanisms, differ radically in the arrangement for depth taking. As regards depth taking, the drifting mines are divided into two classes:
- The fixed depth mine which has a slight negative buoyancy and is suspended from a small buoy floating on the surface.
- The oscillating mine which has no supporting buoy, but regulates its depth by hydrostatic pressure or by vertical movement of the mine in the water.
The advantage of the fixed depth type of drifting mines is its simplicity. No elaborate or delicate mechanism is required to keep the mine at its proper depth. The advantage of the oscillating type is the absence of any indication on the surface of the location of the mine. Drifting mines have been so little used in the past that no line is clearly marked for their future development.
After the Russo-Japanese War certain limitations were placed on the design and use of mines by Convention VIII of the Second Hague Conference of 1907. This Convention is binding only when all belligerents have ratified or adhered. The only principal naval power which has not yet ratified the Convention is Italy. The Convention prescribed:
- It is forbidden to lay automatic contact mines off the coasts or ports of the enemy with the sole object of intercepting commercial shipping;
- Mines are to become inoperative within a limited time, precautions must be taken to safeguard peaceful shipping, and the neutral nations must be notified of danger zones as soon as military exigencies permit;
- Anchored contact mines must become harmless as soon as they have broken loose from their moorings;
- It is forbidden to lay unanchored automatic contact mines except where they are so constructed as to become harmless one hour at the most after the person who laid them ceases to control them.
Manifestly, the first two conditions accomplish very little in limiting the use of mines by a belligerent. The last two conditions appear to have been quite generally disregarded in the World War, except when observing them was to the interest of the side which laid the mines. Our own anchored mines were so designed that they became ineffective if they broke adrift, and our drifting mines are designed with a sinking valve to sink the mines one hour after they are laid.
In the design of all mines, the safety of the laying vessel is an important consideration, and mines contain safety features to make them inoperative while the mines are on board and for a short time after they have been laid. The control over the contact mine ceases, however, after the mine first becomes inoperative, and a mine which combines the simplicity of the contact mine with the safety of the controlled mine is yet to be found.