From the very beginning of the war, Germany adopted a policy, and vigorously pursued a campaign of mine laying in the vicinity of the English coast; apparently she lost no opportunity of laying floating mines, where the water is too deep for anchorage, and fields of anchored mines in shoal water. To this policy, together with her universal reliance on the submarine, may be credited many of her successes, while England had recourse principally to gunfire. In the event of a decisive engagement in the North Sea these methods might easily have had a more far-reaching effect than is, at first glance, apparent. Certain it is that they caused the British fleet to concentrate at various bases on the coast of England and Scotland, where it, in turn, was thoroughly protected by mine-fields. And this widespread use of the mine has had another effect, in that it has served to create and develop that miniature navy, the trawler arm of the Grand Fleet. All along the coast of Great Britain these small craft gathered in surprisingly large numbers; in one port alone, over a thousand trawlers have been fitted out, and, it is said over 12,000 men were required in this branch of the service.
In the war mines were used for two distinct purposes: (1) To close military ports; (2) As a distinct operation against a hostile fleet or ship. The object of these uses requires no explanation. But, in addition to these recognized uses, mines have also been used in connection with no definite military scheme. The Germans seem to have scattered them on the chance of destroying individual men-of-war or merchant vessels of the enemy. An article of the Hague conference forbids the laying of automatic contact mines off the coast of the enemy with the sole purpose of intercepting commercial shipping. Germany signed this article "with reservation;" and this paper is not concerned with the situation from the standpoint of international law, except, in passing, to invite attention to the fact that, as a result of serious damage to neutral shipping, we, in our note of February 22, 1915, suggested that isolated drifting mines should be laid by neither party, that anchored mines should be laid exclusively for defensive purposes within range of harbors, to become harmless after breaking loose from their anchorages."
Considering first the laying of the mines for the purpose of closing military ports, and the effect thereof on naval strategy and tactics, reliable sources indicate that, during the latter part of the war, the following was the situation in regard to the ports of the North Sea.
Early in the war British submarines succeeded in entering the harbor of Kiel, only, as might have been anticipated, to find the German fleet protected by many minefields. Cuxhaven was heavily mined, as well as the mouths of the Weser, Jahde and Elbe, the mouths of the Scheldt and the approaches to Antwerp, the waters around Borkum, and, of course, Helgoland. There was no opportunity for these minefields to cause any actual damage to the British fleet. On the contrary, they proved to be a source of danger to the Germans themselves. For we read of a German patrol boat striking three mines near Borkum; and, pursuant to striking a chain of mines that blocked the entrance to Jahde Bay, the cruiser Yorck was totally destroyed, a tragedy that resulted in the sentencing of her commander to two years' detention in a fortress as a penalty for his negligence.
But even though these minefields in the vicinity of German ports caused no direct damage to the British, their strategical and tactical value has been vast. After the injuries to the Lion resulted in the temporary withdrawal of Sir David Beatty from the Dogger Bank engagement, the British fleet gave up the chase and countermarched at a distance of about fifty miles from Helgoland. The first English report of the battle states that the reason for abandoning the pursuit was due to the danger of running into minefields. In confirmation of this, there is the German report that Von Hipper, shortly after sighting the British squadron, some 120 miles from Helgoland, changed course to the southeast in order to draw the enemy toward the minefields. The mooted question as to whether the British would have turned back had Sir David Beatty been able to hold his place in formation does not now concern us. The fact remains that the abandonment of the pursuit presumably because of the danger from mines may, as one writer has aptly pointed out, have robbed the British of a complete victory "in the Nelsonian sense."
Early in the war, the British Admiralty, as a result of the great activity of the Germans in mine laying, developed, on a considerable scale, an aggressive policy in this form of war on the sea. To reduce the risk to non-combatants, the Admiralty announced the parallels and meridians bounding a rectangle in the North Sea which was to be considered as a danger area, supplementing the notification with the caution: "Although these limits are assigned to the danger area, it must not be supposed that navigation is safe in any part of the southern waters of the North Sea. Instructions have been issued to His Majesty's ships to warn east-going vessels of the presence of minefields." In May, 1916, it was deemed advisable to extend the eastern and southern limits of the danger area and to publish the new limiting parallel and meridian.
In October 1914 the battleship Audacious sank after striking a mine off the North Irish coast, presumably while seeking suitable waters in which to hold her great gun practice. Shortly after this disaster neutral vessels were warned of the presence of mines off the north coast of Ireland, and there was set out in the North Channel a danger area the limits of which were made public. The purpose of this move was to close the greater portion of the North Channel, leading from the Atlantic into the Irish Sea. The parallelogram limiting this danger area occupied the north part of the channel, leaving a narrow passage between it and the Irish coast. This passage was to be used only in daytime, and no ship was to be within four miles of Rathlin Island between sunset and sunrise. This rendered it a simple proposition to examine vessels entering the Irish Sea from the westward, and made it extremely difficult for enemy minelayers to operate. It is also probable that this step had the effect of diverting the greater part of Atlantic traffic around the south of Ireland, where, owing to more sea room, there are greater facilities for maneuvering to avoid the attack of submarines.
In the Baltic, Germany originally conceived the project of forcing an entrance to Riga and landing an expeditionary force to co-operate with the left wing of her army. This she was unable to accomplish because of the well guarded minefields at the entrance of the gulf. In addition to Riga, the coast waters of the Aland archipelago and the entrances and exits of the Gulf of Finland were heavily mined. The existence of minefields in international waters south of the Danish island of Saltholm, off the Drogeden lightship, along Falsterbo Reef, and near the approaches to Stockholm caused no little anxiety to the powers of Norway, Sweden and Denmark, striving as they were alike to protect the interests of neutrals and to avoid giving offence to either belligerent.
In the Asiatic, German minefields in Kiaochou Bay prolonged the defense of Tsingtau against the British and Japanese squadrons and effected the loss of the Japanese cruiser Takachiko and several torpedo boats. From a plan obtained after the capitulation, it is known that Germany had planted at least 300 mines in the harbor of Laoshan.
Perhaps of all the theaters of the war, the Dardanelles lent themselves most favorably to the use of the mine. It was possible to render this whole area impassable by the use of the three recognized types—contact, observation and floating. While the velocity of the current offered certain difficulties to the use of the contact type, the narrowness of the channel facilitated the use of the complicated device necessary to explode observation mines from the shore; and the constant danger from floating mines drifting down with the current from the sea of Marmora was one against which it was necessary to maintain eternal vigilance. It is known that contact mines, to the number of forty, were laid in double line from Kephez to Suandere. Yet all precautions taken by the Germans in the Dardanelles did not entirely suffice; witness the brilliant exploit of Lieutenant Holbrock, who, despite the difficult current, ran his submarine into the Dardanelles, dived under five rows of mines, and sank the Turkish battleship Messudiyeh, which was guarding the field.
Early in the war the port of Bourgas in the Black Sea was closed. Varna could be entered in daytime only, and vessels were forced to stop at Kamtchia and wait for a pilot.
The enemy mined the bay of Cattaro in the Adriatic. British and French torpedo-boats, dragging the bay, recovered more than 1000 mines; and the French destroyer Dague was blown up while dragging off Antivari.
To illustrate the second use of the mine—as a distinct operation against a hostile fleet or ship—there is, early in the war, the engagement that resulted in the mutual destruction of the Koningen Luise and the Amphion. The Koningen Luise was a Hamburg Amerika passenger vessel which had been converted into a minelayer. After she had probably laid a line of mines from Aldebrugh ridge to the northeast, she was sighted about sixty miles off the coast of Suffolk by the British light cruiser Amphion. The minelayer was pursued for 30 miles, overhauled and sunk. After picking up the survivors, the Amphion, on her return to port, when nearing the scene of the minelayer's operations, altered course to avoid the supposed danger; however, despite this precaution, she struck two mines and sank.
Subsequent to the light engagement in the North Sea that occurred during the first month of the war. Sir David Beatty reported to the Admiralty: "Our destroyers reported the presence of floating mines to the eastward, and I considered it inadvisable to pursue her." It is probable that the "two-funneled cruiser" the Lion was then pursuing had saved herself by launching floating mines.
The destruction of the battleship Formidable in the channel was due to a floating mine or to a submarine. And the loss of the King Edward VII. was presumably due to her striking a mine in the North Sea, off Spurn Head; the German Admiralty, in fact, attributed the credit of the destruction of this vessel to the mysterious commerce destroyer Moewe.
Especially in the Dardanelles has there been ample opportunity for the use of floating mines against a hostile fleet. Utilizing to the very fullest extent the strong current that sets from the Sea of Marmora to the Mediterranean, the Turks employed the floating mine after the fashion of a torpedo. And it is to this weapon that the loss of the battleships Irresistible, Ocean, and Bouvet, and the injury to the battle cruiser Inflexible have been attributed. Also the destruction of the battleship Russell in the Mediterranean was probably due to the explosion of a mine.
In addition to carrying out vigorously the policies hitherto recognized in regard to the use of the mine, the Germans inaugurated and pursued more aggressive measures. Making use without doubt of their submarine minelayers, they pushed their campaign to points surprisingly near the British coast. Neutral and enemy vessels have been destroyed off the mouth of the Tyne, many of them within sight of Newcastle and Dover. The Audacious met her fate due to striking a minefield that the enemy had laid off the Irish coast. In fact, the British Admiralty issued warnings to the effect that neutral shipping was endangered by mines in this vicinity, thus admitting that German activities in this direction had extended even to the coast of Ireland. Mention has already been made of the counter measures adopted by England in the North Sea, the English Channel and the North Channel pursuant to Germany's vigorous campaign.
To say nothing of the loss of a host of smaller vessels, the destruction of the battleships Audacious, Irresistible, Bouvet, Ocean, Formidable, Russell, and King Edward VII., is a large toll exacted of the allies as a result of mining operations. Nor should we overlook the destruction of the Hampshire, with the death of Lord Kitchener, and the incalculable loss to England that ensued therefrom.
As to the character of the mines used, it has been pointed out that they have been of the observation, the contact and the floating types.
In regard to the mechanical features of these mines there is, of course, but little available that is not confidential. But it is of interest to note the elementary details of a mine used largely by the Turks in the Dardanelles, called the Leon torpedo mine. This mine, invented by a Swedish officer, Captain Karl Leon, may be launched simply by placing it in the water, or by ejecting it in the same manner as the ordinary torpedo. Cylindrical in shape, the mine is divided into two separate compartments; the upper contains the explosive, together with the firing apparatus in a central tube; the lower compartment is itself divided into two sections, the upper of which contains a battery of accumulators, and the lower the machinery. Weights are arranged so that the mine, when submerged, retains a vertical position. This is accomplished by means of a chamber that fills with water, thus giving the mine a tendency to sink. The speed at which this chamber fills, and hence the rate at which the mine sinks is controlled by a valve. Even with a full reservoir, the mine is only slightly heavier than water, so that it never sinks rapidly. When a certain depth has been reached, the pressure of the outside water acts on a hydrostat which is arranged to close a switch connecting the battery to a motor which drives the mine propeller. The mine then commences to rise. When a point within five feet of the surface has been reached, in consequence of the reduced pressure on the hydrostat, the battery switch opens, the motor stops and the mine sinks. It is possible to adjust the hydrostat so that the maximum immersion may be obtained within limits of five to ten feet from the surface. A clock device may be set to limit the length of time within which the mine is to remain active. This control is accomplished by interrupting the current at the end of the time set. The clock device may likewise be used to delay the time at which the mine is to become active. In the latter case, the mine remains at the bottom until, at the expiration of the time designated, the motor switch is closed and the propeller functions. A stabilizer is fitted in order to compensate for different densities of water.
The Leon mine may be used as a distinct operation against a hostile fleet or ship, or in the attack on a tidal port. For the latter purpose, mines are launched when the tide is flowing, and travel with the ingoing water. Where a long estuary is to be traversed, the clockwork is arranged to function after a given interval when the tide ebbs, the mine sinks, to rise again when the flood renews. It is also possible so to arrange the mechanism that the battery is connected with the motor only at the end of a given period; when so adjusted, the mine finally comes to the surface and remains there until the battery runs down.
For the purpose of mine-laying, all sorts and conditions of vessels were pressed into service. They ranged from converted destroyers and passenger steamers to the German submarine minelayers.
The French found very valuable three vessels of the Casablanca class. Originally built for destroyers, with a displacement of 950 tons, they proved to be too slow for this service. Accordingly, they were converted into minelayers, a process that raised their tonnage to 1020, and still further reduced their speed. Each of these vessels carried about 100 mines. The Casabianca was destroyed by one of her own mines while engaged in hazardous night work in the Aegean, but her sister ships, the Cassini and the d'Iberville rendered very valuable service. Later types of French minelayers were smaller in displacement—566 tons—but they carried 120 mines weighing 550 kilos each. Of this type were the Pluton and the Cerbere.
The German minelayer Konigin Luise was a passenger steamer of 2200 tons, while the Russians successfully used vessels as large as the Prout, of 5000 tons, with a capacity of 700 mines.
For months after the outbreak of the war, there was great perplexity over the facility with which the Germans were able to plant mines within short distances of the English coast, and the British press was rife with statements to the effect that these mines had been laid by "pleasure steamers and fishing smacks," vessels flying neutral flags and merchantmen. In spite, however, of the vigilance of the British patrol, it does not appear that a single vessel of this description was actually captured or sunk while in the act of sowing mines while flying a neutral flag. It would therefore seem appropriate to attribute the greater part of this mine-planting to the activities of submarine minelayers which, it is now evident, Germany used for some time. The capture of the submarine minelayer UC-5 cleared the mystery. This little vessel—the first of her kind captured— was 100 feet in length; she had a beam of 10 feet, 6 inches, and drew 11 feet when awash she was propelled by a six cylinder Deisel engine of 250 horsepower. According to one of her crew—her complement was five officers and 13 men—she had made 19 trips from Germany to the British coast; on her 20th she was captured by a British patrol vessel. It is said that in the course of her various trips she laid over 200 mines in routes frequented by merchant vessels. The UC-5, one of the forerunners of a numerous class—was constructed in four sections. On top of the hull was a light superstructure of thin plating to make a level deck. Conning-tower, periscope and wireless mast were placed amidships. The entire hull forward of the conning-tower was a mine-carrying case. Countersunk in the deck was a row of six gratings; beneath each grating a steel chute slanted from top to bottom. This steel tube was fitted with flanged runners on which slide four stays holding the mines, of which each chute contained two. The mines were released by the operation of a lever fitted inside the hull. Once released, the mine sank to the bottom; then angle irons surrounding it were automatically released at the top, and, dropping outward and downward, lay on the bottom to form a rest for the mine. The anchor remained on the bottom, while the mine itself rises, hauling after it a steel wire which unwinds from a drum revolving within the anchor. A hydrostatic valve was fitted to determine the depth at which the mine was to float below the surface.
Countermining operations took the usual forms of dragging, sweeping and detonating. There is little available data in regard to the last named method. Electricity has probably been used for this purpose; and many mines have been exploded by gunfire in the English Channel and off the coast of Antivari.
For the purpose of dragging and sweeping, torpedo-boats and destroyers have been especially valuable. In the Adriatic, sweeping operations by allied torpedo-boats resulted in the recovery of over 1000 mines in the Bay of Cattaro alone. The Germans effected their one entrance to the Gulf of Riga after several days of difficult mine-sweeping. British and French destroyers rendered especially valuable service in the Dardanelles. The entrance to Laoshan Bay was patrolled by sweeping destroyers with the assistance of trawlers and patrol boats; and several Japanese destroyers were blown up in the course of the operations.
Finally, the fleet of trawlers rendered inestimable service in mine-sweeping operations. It has been pointed out that this arm of the British fleet has attained astounding proportions; it is a veritable mosquito fleet in itself. Following raids on Scarborough and Hartlepool, over 1500 mines were picked up by trawlers in one week. In the course of work of this nature many boats were lost; frequently mines exploded in the nets. In addition to their value in work of this nature, it is claimed that there is no better protection for a battleship at anchor than a surrounding cordon of trawlers when danger from mines or submarines is apprehended. England has thoroughly demonstrated the value of the trawler fleet. Let us bear in mind that, if the time ever comes to require its service, it would be well for us to have ready to our hand a defensive weapon of such magnitude and efficiency.