On October 2, 1914, the first line of 1,264 mines was laid by the old cruisers in an area om. north of Ostend. This had the effect of forcing neutral ship ping to pass through the Downs. Unfortunately, the British mines then in use proved so defective that for a time minelaying had to cease; and although in 1915, after some technical improvement, some 15 more minefields were laid, it was not until 1916 that attention was concentrated on providing a mine of the calibre of that used by the Germans.
One of the principal British minelaying operations of 1916 was a coast barrage, consisting of a double line of deep mines, running for 4om. from the Belgian coast, at a distance of 12m. from the shore. It was supplemented by mine nets laid by the Dover drift ers. The work took five weeks to complete; but only one sub marine seems to have been accounted for by it. The end of the year saw the institution of a mining school at Portsmouth for re search and development.
On the assumption that the Belgian coast barrage had been effective, a similar barrage was completed in Feb. 1917 across the Straits of Dover; but the mines dragged and had to be swept up.
It was, however, relaid by the end of July 1917. In Jan. 1917 it became essential to encircle the Heligoland Bight and thus to surround all exits from German ports; but the shortage of mines at the time caused the operation to be postponed, nor was the British mine considered suitable for it. However, towards the end of 1917 the "Abdiel" and five minelaying submarines had laid nearly 16,00o mines in the German Bight; and these accounted for a certain number of German destroyers and minesweepers. The mine used in the later stages of this operation was the new British H2. In due course the new H2 mine was delivered in sufficient quantity for the long-delayed defensive minefields to be begun by the British, and an extensive new barrage in the English Channel was then completed. Between Folkestone and Cape Gris Nez 9,500 mines were laid in 20 parallel lines, the shoals of the Varne and the Ridge dividing the area into three sections. This barrage effectively closed the Channel exit to the German submarines, nine of which were lost in attempts to pass it.
The entry of the United States into the War admitted of a large augmentation in mines and in minelayers ; and an attempt was made to close the northern exit from the North sea by a mine barrage between the Orkneys and the Norwegian coast (see plan). This operation was under taken by both British and U.S. minelayers. The latter formed a base at Inverness, and supplied ten large minelayers with a total carrying capacity of over 5,500 mines.
The vast area covered by mines can best be appreciated by a reference to the plan, which gives an idea of the work carried out by the U.S. minelayers. Difficulties were encountered as the operation proceeded. A proportion of the American mines ex ploded prematurely; while a number of British mines took up a shallower depth than intended, and had to be swept up and relaid. The complete operation, however, was finished by June 1918. It must not be supposed that the whole water available for a sub marine was effectively covered by this minefield; but the dangerous area was greatly increased and an effect on the morale of the Ger mans quickly produced. In July German submarines began to
creep past in Norwegian waters ; but the Norwegians closed this coastal lane to both belligerents by minefields of their own. Of the mines laid in the Northern Barrage 56,033 were American and 15,093 British. All the time the encircling of the Bight had been going steadily on, and some 21,000 mines were in place by the date of the Armistice. During the period of the War, approxi mately 172,000 mines were dropped in the North sea and Channel by the British and American minelayers, the very great majority of which were laid during the last 18 months of the War. The Italian Navy laid 12,293 mines during the War chiefly in the Adriatic.
In the early part of the War, the Germans used surface vessels for minelaying and the fields consisted of large groups of mines concentrated in areas where they were likely to damage naval vessels. For instance, on Aug. 5, 1914, the "Konigin Louise" laid a line of about 15o mines off the east coast of England and on Dec. 16, 1914, under cover of the raid on Scarborough the "Kolberg" laid 180 mines near Scarborough Bay. After 1915 German minelaying in British home waters was carried out almost entirely by submarines. These usually con fined their mines within an area of two or three sq. miles, laying them in groups of four or even less. The position chosen was most frequently near some focal point, buoy or lightship, or at the entrance to a naval base or commercial port. For instance, during the war, over 450 mines were laid by German submarines within a mile of the Shipwash Light vessel, a position necessarily passed by all traffic up and down the east coast war channel, by the convoys to and from Holland and by those destroyer flotillas based on Harwich. The Germans also allotted to each of these submarines a particular stretch of the British coast. The flotillas working from Flanders covered the coast from Flamborough Head south about to the Clyde, also the northern French coast ; the high sea, or large boats, working from the Elbe, were responsible for the rest of the English and Scotch coasts, and the whole of Ireland. Each commander being restricted to work in his indi vidual area, the danger of striking previously laid mines was minimised. The commanders, moreover, by this arrangement, got quickly into touch with the local movements of the traffic, the method and capacity of their opposing minesweepers and the coastal navigation within their beats. In most cases after some 10 to 14 days a commander would not hesitate to pass over a position where he had previously laid mines. He would be con fident that his mines had been discovered and cleared if shipping had been seen in the area. Minelaying from surface vessels was confined to disguised raiders such as "Wolf" who laid small groups of mines in various parts of the world including the Cape, Bombay, Colombo and Australian coasts. Altogether I ',coo mines were laid by German minelayers in British home waters.