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Rh technical design of the mine, and the operation of minelaying. The offensive power of the mine and its place in naval strategy had not been appreciated at the outbreak of war. Its use for the defence of harbours had been abandoned by Lord Fisher several years before; and though a squadron of seven old cruisers had been converted into minelayers (“Andromache,” “Apollo,” “Intrepid,” “Iphigenia,” “Latona,” “Naiad” and “Thetis,” 3,400 tons, i8-ft. draught, 14 knots)., more than two years were to pass before discovering a reliable mine. This was properly the task of the torpedo school-ship “Vernon,” but hampered by lack of funds its work was not attended with very happy results. The details of the Russian mine were well known to the British authorities. It was simple and effective and the pattern was adopted by the Germans with conspicuous success, but it cost some 200 and the British had to be content with a cheaper one. This was the naval spherical mine, and at the out- break of the war there were 4,000 available.

The original plans had provided for laying mines in the southern part of the North Sea, and the notices to mariners and neutrals were ready to print when it was found that the pistol was too sensitive and the mooring-wire too weak. The older admirals were also inclined to deprecate them, on the grounds that the British should keep the sea as open as possible for the use of their own ships. The sinking of the “Cressy,” “Hogue” and “Aboukir,” which left the Belgian coast open to attack, startled the navy out of this opinion, and it was decided by Great Britain to lay mines in the North Sea. This was notified to neutrals, and the first line of 1,264 mines was laid on Oct. 2 1914, 10 m. N. of Ostend. In Nov. mines were reintroduced for defence of harbours, and a special corps of Royal Marine submarine miners was started to manipulate them. By the end of 1914 some 2,000 mines had been laid in the southern part of the North Sea, which had a good effect in forcing neutral shipping to pass through the Downs, and for a time deterred enemy sub- marines from approaching the Channel. During 1915 a number of fields were laid in German waters and the minelaying squadron was greatly strengthened. It now consisted of the “Princess Margaret” (Canadian Pacific railway, 5,440 tons, 21 knots, 500 mines), the “Paris” (cross-Channel, 2,030 tons, 25 knots, 80 mines), “Angora” (Calcutta to Rangoon, 300 mines), “Biarritz” (S. E. & Chatham railway, 2,700 tons, 21 knots, 305 mines); but the mine still lagged behind the minelayer, and in June the British Elia mine was found to be so defective that minelaying ceased for a time.

On May 27 1915 the loss of the “Princess Irene,” which was blown up at Sheerness by an internal explosion, was a severe blow to the minelaying service. In the Narrows 15 more mine- fields were laid during the year, chiefly between the Goodwins and the Belgian coast.

By 1916, the importance of mining in North Sea strategy was beginning to be realized, but an efficient mine was still lacking. There could be no question that the German mine was much more efficient. It was a spherical mine, fitted with lead horns containing a sealed glass tube which held the liquid for exciting an electric cell. When the mine was struck, the lead horn bent, the glass tube broke, the liquid ran into the cell and the mine fired. It was held to the sinker by a catch, and went to the bottom with it when dropped, leaving the water free for the minelayer. After an interval of half an hour or so, glycerine escaping from a dashpot gave play to a plunger which released the catch, and the mine rose gradually to the surface, uncoiling a double mooring-wire from inside the sinker. On reaching its correct depth from the surface, a hydrostatic valve released a strong spring clamp, which clamped the mooring-wire and held the mine at its correct depth. The British mine was more complicated, and, instead of concentrating attention on the production of a good mine, efforts were wasted in an attempt to devise a combination of mines and nets which achieved little or nothing.

The ordinary minefield was usually laid so as to be about 10 to 15 ft. below the surface at low water, but the success of the submarine gave rise to the conception of deep minefields laid at about 60 to 1 50 ft. to intercept the submarines when submerged.

The ordinary surface minelayers now began to be supplemented by submarines and destroyers; the 24 was one of the earliest boats to be fitted for this purpose, and the destroyer “Abdiel” was equipped to carry 80 mines. They were both busy laying minefields in German waters in 1916. The 24 laid a field close to the Elbe on March 3, but never returned from her next trip on March 21 ; and a field was laid by the “Abdiel” off Horn's Reef on which the “Ostfriesland” struck on June 1 when returning after Jutland. One of the principal British minelaying efforts of 1916 was the Belgian coast barrage, consisting of a double line of deep mines laid about 12 m. off the Belgian coast for some 40 miles. It was begun from Dover on April 24 1916, and consisted of some 1,565 mines, which took some five weeks to lay. The minelayers engaged were the “Princess Margaret” (Capt. Lockhart Leith), “Orvieto” (Capt. H. Smyth), “Biarritz” (Capt. E. Morant), and “Paris” (Comm. John May), under Capt. F. S. Litchfield Speer, supported by Dover and Harwich destroyers and the monitors “Prince Eugene” and “General Wolfe.” Three German destroyers sallied out from Zeebrugge on April 24, but were engaged by the “Medea” (Comm. V. F. Gibbs), “Melpomene” (Lt.-Comm. H. De Burgh) and “Murray” (Lt.-Comm. H. Taprell Dorling), and driven off, though the “Melpomene” was badly hit by shore batteries.

The lines of mines were supplemented by mine nets laid by the Dover drifters about a mile to rearward of the mines.

This was the first big undertaking against the submarine, and did not meet with conspicuous success, for with the exception of the UB3, destroyed by a drifter on April 24, no submarine seems to have been sunk by it.

The end of the year saw the institution of a mining school for research and development, and this segregation of the work from the torpedo school, already burdened with torpedoes, electrical engineering and wireless, probably contributed to its efficiency. The Belgian coast barrage was erroneously supposed to have been the cause of the reduced submarine activity in the Channel during the summer, and a similar barrage was now be- gun across the Straits from the Goodwins to Snouw Bank on the Belgian coast. The nets were 60 ft. deep, each fitted with two mines and hanging from buoys 500 yd. apart. A line of deep mines was laid on their south side, from 54 ft. below the surface to within 30 ft. of the bottom. This field was completed on Feb. 8 1917 by the “Princess Margaret,” “Biarritz” and “Paris.” Later, the mines dragged into the nets and sank the Trinity House tender “Alert” while tending them. It was considered necessary to sweep the field up and relay it, which took the best part of June-July 1917. The work of 1917 lay chiefly in Hel- igoland Bight. In Jan. 1917 Adml. Beatty urged the necessity of mining on the largest scale, and proposed a line 157 m. long encircling the Bight, to be watched by light cruisers and de- stroyers. This was the first task given to the Plans Section, but unfortunately there was a great shortage of mines for the work and the British Elia mine was considered unsuitable. As these fields were intended to be permanent, an official notification of the field was made on Jan. 25 1917.

The Dutch Government, for the convenience of their trade, moored a line of four light-vessels and seven light-buoys which ran for some 180 m. N. and S. to the west of the western limit of the British notified area (light-vessels in 56°N., 5°E. ; 54° 47' N., 4°8'E.; 53°29'N., 4°2'E.; 53°N., 4°5'E.). Their lights, blazing out at night and immune from attack, became so well known a seamark as to earn the name of “Piccadilly” from the submarines and destroyers plying to and fro. During the year 1917 15,686 mines were laid by the “Abdiel” and the minelaying submarines (E24, 41, 45, 51, 34) and led to the loss of a number of German destroyers and minesweepers. The fields in the southern portion of the North Sea were reinforced by 1,120 mines in June 1917, and during the summer a mine-net barrage was laid at the entrance to the Adriatic from Cape Otranto to Fano Is., 45 m. long.

In 1917 the British Admiralty realized that minelaying on a large scale ranked as one of the principal operations of the war, though it was not till September that an efficient mine (pattern H2) began to be turned out in sufficient quantities. 