# 1922 Encyclopædia Britannica/Minesweeping and Minelaying

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​MINESWEEPING AND MINELAYING. Among the naval services rendered to Great Britain and the Allies during the World War, none were more conspicuously important than the work of British minesweepers and minelayers; and minelaying was a large item in the naval war record of Germany.
Mines-weeping. As early as 1907, Adml. Lord Charles Beresford, when commander-in-chief of the British Home Fleet, had recommended the use of Grimsby trawlers for the service of minesweeping. A trawler reserve, R.N.R. (T.), had been constituted under an inspecting captain of minesweeping vessels, and the system worked so well that by Aug. 8 1914, 96 hired trawlers had put to sea. The needs of minesweeping had, however, only partly been foreseen. When the war broke out the only minesweepers with the fleet were six torpedo gunboats fitted with the “A” sweep, a single wire kept at a required depth by waterkites and towed between two sweepers 500 yd. apart. It soon became evident that minelaying played an important part in German strategy, and after the “Amphion” had been sunk on the field laid off Aldeburgh by the “Konigin Louise” on Aug. 5, a hundred additional trawlers were ordered and Lowestoft became the principal minesweeping base on the east coast. On Sept. 1 Rear-Adml. E. Charlton was appointed Rear-Admiral Minesweeping on the East Coast, in charge of minesweeping operations and technical arrangements, leaving the inspecting captain to attend to the business of supply.
Minesweeping at this time was largely in the experimental stage and some time elapsed before it was able to cope with the magnitude of its task. One of the first steps taken to ensure the safety of shipping was the institution of a war channel up the east coast, clearly marked by buoys 2 m. apart, from the Downs, past the Shipwash, Newarp and Cromer's Knoll to Flamborough Head. This was swept daily by local trawler flotillas and provided a safe channel up the east coast. Trawlers, ​however, were too slow for emergencies, and ordinary excursion paddle-steamers of light draught and good sweep were intro- duced with very successful results. A special design of sloop the “Flower” class of 1,200 tons, 250 ft. long, u ft. draught and 16 knots was laid down in large numbers, but these were not ready till April 1915. The loss of the “Audacious” off Tory I. (Ireland, N.) on Oct. 27 still further emphasized the necessity of a large and efficient minesweeping service. The minefield laid by the German s.s. “Berlin” consisted of some 200 mines running approximately N.E.-S. W. north of Tory Island. It was not definitely located till Dec. 20, and, though 43 mines had been swept up and 70 drifted ashore by the end of April, was not cleared till July 1915. It must be remembered that the loss of a ship or the discovery of a mine merely served to indicate the proximity of a minefield. Before its extent could be defined and the clearance completed a number of exploratory sweeps were required which were often delayed by bad weather. The German mines laid during 1914 were laid by surface craft in the following areas:—
They accounted for 42 merchant vessels or approximately one vessel for 24 mines. The measures taken to meet the danger consisted in the establishment of a war channel and the preliminary steps for a great expansion of the minesweeping service.
Minelaying played an important part in the German raids on the east coast, and the raid on Dec. 16 1914 was intended to cover a minelaying operation by the “Kolberg,” in which she laid 100 mines off Scarborough. Two of these mines were found by gunboats on Dec. 19, and half an hour later a Grimsby trawler minesweeping unit brought 18 to the surface simultaneously. Two of its trawlers struck mines and the field was not finally cleared till April 1915, 69 mines being accounted for out of 100 laid, with heavy losses to shipping, including 7 British and 7 neutral steamers, 2 trawlers, 4 minesweepers and an armed yacht.
By April 1915 the minesweeping forces had increased con- siderably and were distributed as follows: Grand Fleet, 6 gunboats, i sloop and 9 trawlers; Scotland, east, 47 trawlers; Humber, 6 paddlers, 30 trawlers; Lowestoft (war channel), 47 trawlers; Harwich and More, 33; Dover, 12; South Coast, 24; West Coast, 4; Clyde, 6 paddlers (fitting out). The principal minefields laid by German surface craft in 1915 were:—
The Eastern Dogger Bank minefield was large but not a single British vessel of any size was lost in it. Sixty-nine mines were swept up there and the swell of the winter sea probably completed the task of clearance.
The fields off the Humber were responsible for the loss of 4 British, and 5 neutral steamers and 3 minesweepers, but the field was defined by May 1915; 127 mines were swept up that month and by the middle of July it was clear. The fields laid by the “Meteor” in Aug. 1915 and by the “Moewe” on Jan. 1 1916 were aimed directly at the Grand Fleet. The “Meteor” made the Scottish coast at dusk on Aug. 7 and, starting from a position about 22 m. N. of Kinnaird Head, laid 380 mines in the approach to the Moray Firth during the night. The first notification of them came from a Cromarty trawler minesweeper making a routine sweep on the morning of Aug. 8. The destroyer “Lynx” was lost the same day and the sloop “Lilac” had her bows blown off. After clearing a 10-m. channel along each shore and removing 222 mines, the rest of the field was left unswept as a protection against similar attacks. In the final mine clearance in 1918 only four mines were found in it.
The German minefields on the east coast gave rise to the erroneous idea that they were associated with a prospective landing operation. An equally erroneous idea that mines were laid by neutral trawlers obtained so firm a hold in the Grand Fleet that it led the commander-in-chief to ask for the exclusion of all neutral trawlers from British ports.
In the Mediterranean minesweeping played an important part in the attempt to force the Dardanelles. The problem was the same as that which confronted the Germans at Osel in the Baltic in 1917. The task was one of peculiar difficulty, for it meant sweeping under the fire of batteries, and the strong current reduced the speed of trawlers with sweeps out to less than 3 knots. It was a task which required high-speed sweepers and a highly trained personnel, and even with their agency its feasibility may be doubted. The technical difficulties of the task were greatly underestimated. It was regarded as a simple piece of work which any vessel fitted with a sweep could perform, and it was attempted with a motley collection of slow trawlers, assisted by a parcel of destroyers fitted with sweeps for the first time. The sweep principally used at this time and throughout the war was the “A” sweep, consisting of a single 2j-in. wire towed between two ships steaming 500 yd. apart, with its depth regulated by a water-kite 12 ft. long and weighing a ton. The end of the wire had to be passed from one vessel to the other and to do this rapidly under fire required an exceptional combination of training, skill and courage. In the case of fast sweepers, the momentum of the wire was sufficient to cut the mooring of the mine, but slow sweepers in the early years of the war had to take their sweeps into shallow water where the mines could be seen and sunk. This made sweeping slow work, and it also meant that the “A” sweep was really only effective by day; so that sweeping a minefield under heavy fire was almost impracticable.
The year 1915 saw an important development in the use of submarines for minelaying by the Germans. The Flanders Flotilla were the first workers in this field and their mines were first discovered off the S. Foreland on June 2 1915. These were laid by small boats termed UC boats, equipped with 12 cylindrical mines with charges of 350 Ib. of T.N.T., carried in vertical shoots. The mine dropped with its sinker to the bottom and was released from the sinker by a “dashpot” arrangement about half an hour after reaching the bottom, giving the submarine time to get clear. The mooring- wire coiled into the sinker was drawn off by the mine as it rose, and when the proper depth was reached it was gripped by a strong spring clamp released by a hydrostatic valve. Submarine minelaying threw a heavy strain on the minesweeping forces at Harwich, Dover and the Nore, which were the areas principally affected at first, and the continuous location of small groups of mines gave rise to an incessant stream of orders for the diversion or stoppage of traffic which greatly hampered coastal navigation.
The Germans report having laid 648 mines between Grimsby and Dover by submarines in 1915, of which 150 were laid in the Dover area (not including the Belgian and French coasts), 180 off the Nore, 306 in the Lowestoft area and 1 2 off Grimsby. The number of mines swept up in this area was approximately 500, and the losses in the last six months of the year showed a serious increase, comprising 3 destroyers, 5 supply ships, one hospital ship, 2 Trinity House vessels, 34 British steamers, 24 neutrals, 10 fishing boats, 15 minesweepers (3 paddlers, 9 trawlers) a total of 94 vessels. In June 1915 the Germans had extended their minelaying to Archangel, and a unit of 6 trawlers had to be despatched there; the unit destroyed over 150 mines by October, with the loss of H.M.S. “Arlanza,” one trawler, 6 British steamers, one Russian and 2 neutrals.
The “Actaeon” sweep, called after the parent ship of the Sheerness torpedo school, came into use at this time. It was a single-ship sweep, consisting of a light wire, a small kite, a depth float and an explosive grapnel, and was towed from each quarter of a minesweeper. On meeting a mine, the explosive grapnel parted its mooring; the sweep proved particularly useful in locating new fields, and had the advantage over the “A” sweep that it could be used by night. ​
The outlook at the end of 1915 was far from bright, and the minesweeping service was barely able to meet the strain in spite of the better design and greater number of its ships.
By the beginning of 1916 the hired paddle-sweeper force had grown to five units, numbering 35 vessels in all, and 14 sloops were in commission with the Grand Fleet. Twenty-four Admiralty paddlers of 810 tons and 63/4 ft. draught were being built and were distributed during the year between the Forth and Dover straits. A new type of twin-screw sweeper of 750 tons with a draught of only 7 ft., called the "Hunt" class, was completing and the whole batch of 12 was allocated to the Grand Fleet. The Burney paravane was also past its trial stage and by the end of the year was supplied to all ships of over 12 ft. draught. This instrument was the product of Lt. Denis Burney's genius. Shaped like a torpedo and about 12 ft. long, it was towed from a special shoe on each side of the bows, being held at its proper depth by a hydrostatic arrangement and at its proper distance by rudders. The mooring-wire of any mine it met was swept clear of the ship into jaws of serrated steel and quickly cut. The mine came to the surface and could be sunk. The "otter" was a modified form of paravane for use in merchant ships where its fitting became compulsory in 1917. The paravane justified its adoption: 180 warships and 2,740 merchant ships were fitted with it; in the former it cut 55 mine wires during the war, and in the latter at least 40 or 50. Another simpler but useful invention, in the form of a special sort of serrated wire for sweeping, also dates from 1916; it could cut through a mine's mooring-rope when towing it no faster than a trawler (4 to 5 knots) .
Surface minelayers were still active, and the raider "Moewe" on her way out to the ocean laid a large minefield of some 250 mines on New Year's day, 1916, on the west side of the Orkneys. Commencing about 10 m. from the Orkneys it ran in zig-zags at 3 to 7 m. from the mainland. The loss of the pre-dreadnought battleship " King Edward VII." on the morning of Jan. 5 was the first sign of it, and two neutral steamers were sunk in the same field. Gales interfered seriously with its clearance but by May some 71 mines had been destroyed. All other German mines laid in 1916 were laid by the submarine flotillas, which were now reinforced by a number of UC boats carrying 18 mines .and by several larger boats (U7i-8o) carrying 34 to 36. Some were attached to the Flanders Flotilla and worked from Bruges and Zeebrugge; others, including the larger minelayers, were attached to the High Sea Fleet and worked from the Elbe. Each of the two flotillas was allotted a separate area of the British coast for minelaying. The High Sea Fleet boats worked N. of Flamborough Head. The Flanders Flotilla area comprised the coastline from Flamborough Head to Dover, the English Channel, the Irish Sea and Irish S. coast to Waterford.
A field laid on the west coast of the Orkneys was to have an unforeseen result. It was laid on May 29 by the U75, one of the large minelayers, as part of the Jutland operations, and at 8 P.M. on June 6 the "Hampshire" on her way to Archangel struck a mine in it off Marwick Head, foundering almost immediately and bringing Lord Kitchener's career to a dramatic close. A trawler unit, searching the spot as soon as the weather moderated, found 15 mines laid at 7 metres in a spot where the strong cur- rent and tidal dip would have enabled the "Hampshire" to pass over them in a normal sea. From May to Oct. 1916 German minelaying in the English Channel ceased as a result of an imperial order, dictated by the American note of April 18, to con- fine submarine warfare strictly to the conditions of prize law. Scheer went further than the imperial command, and ordered his flotillas on April 24 to cease all operations against merchant ships, while the Flanders boats, following suit, limited them- selves to minelaying off Lowestoft, Harwich and the Nore.
In Oct. 1916 submarine operations against merchant shipping were resumed, and minelaying broke out with renewed activity. Mines were laid off the Clyde (Oct. 3) and in November off the Isle of Man. The close of 1916 saw a determined attack by the Flanders submarines against the ports in the Channel and mines were laid off Portsmouth, Dartmouth, Plymouth and Falmouth. The French coast opposite Dover was also heavily mined. In the Dover area 212 mines were laid during the year (not including too off Dunkirk, 100 off Calais and 60 off Boulogne), with a loss of two destroyers, five minesweeping trawlers and 20 steamers.
The unrestricted submarine warfare in 1917 was accompanied by an increase in submarine minelaying, and in the month of April 515 mines were swept up, considerably more than in any previous quarter. The reorganization of the naval staff led to considerable changes in the minesweeping service. The director of torpedoes and mining now took charge of the development, supply and distribution of gear, while the control of operations and the distribution of all vessels was delegated to a captain of minesweeping (Capt. Lionel Preston), who in Oct. 1917 became director of the minesweeping division under the assistant chief of the naval staff. Losses in minesweeping vessels were heavy in the early part of the year, amounting to as many as one per diem in April 1917, but the use of aircraft patrols and of shallow- draught motor-launches proved useful in locating mines and diminished the loss of heavy-draught sweepers. The extended range of enemy minelaying and the heavy losses amongst mine- sweepers led to an increased demand for them. Thirty small paddle-steamers, 10 small tugs and 18 drifters were requisitioned, and orders were issued for the construction of 100 more "Hunt" class (800 tons, 7ift. draught, 18 knots) and 300 drifters.
The war channel now ran up the east coast as far as the Tees in the shoalest possible water, and shipping was released from various night anchorages in the Downs, Black Deep and Great Yarmouth as soon as it had been swept at dawn. Improvements in organization during the year led to a reduction of 20% in merchant-ship losses, though the mines swept up were double those in 1916.
The operations of the High Sea Fleet Flotilla were extended in the spring of 1917 to the Minch and the routes of the west coast of Scotland used by destroyers and fleet auxiliaries, much of the work being done by the U8o, one of the large submarine minelayers. In 1916 195 distinct mine groups had been laid, chiefly on the east coast; in 1917 the number rose to 536 and the sphere of operations extended right round the British Isles. This involved a further expansion of the minesweeping service, and the fast sweepers (sloops, gunboats, paddlers) increased from 93 to 122, the slow (trawlers, drifters) from 430 to 509. The deep water off the Yorkshire coast had been a favourite cruising ground for submarines, but large protective minefields were now laid there as an off-shore protection with good results.
The Harwich area was exceptionally busy in 1917, and its work in that year must rank as one of the principal minesweeping achievements of the war. Mines were regularly laid by German submarines in the latter part of the year to catch the Holland trade, and a new minefield off the Maas Light, laid in April 1917 and regularly renewed, became a source of constant trouble. Out of 680 mines laid 633 were destroyed, with the loss of four merchant ships and eight minesweepers. The enemy had to pay a heavy toll for his work, and lost 12 minelaying submarines in the southern portion of the North Sea during 1917. The port of Liverpool, as the principal arrival base for Atlantic transports, was a constant source of anxiety, and at the beginning of 1917 had only two minesweeping trawlers attached to it. Mines were reported there on March 24 1917, and on April 9 the "New York," with Adml. Sims on board, struck a mine, but the port was fortunately left alone till December, by which time the protective arrangements had greatly improved. Of 45 mines laid in the Mersey area 33 were accounted for, with the loss of five mer- chant ships and one pilot steamer in which 28 pilots lost their lives. In the W., Lough S willy and the approaches to the Clyde were all mined during 1917, some 88 mines being laid in this area and off Belfast, of which 72 were destroyed, with the loss of four steamers, one destroyer and five trawler minesweepers. The south coast of Ireland also became a regular region of visitation, and the small tidal range and heavy swell made minesweeping particularly dangerous there. The loth Sloop Flotilla was sent from Immingham to Queenstown in Feb. 1917 to cope with the new danger, and two of its sloops were mined in the following ​month. It was off this coast the UC44 was working in summer, to be blown up on Aug. 4 by one of her own old mines off Waterford. Out of 380 mines laid by the High Sea Fleet minelayers and 36 by the Flanders Flotilla in this area, 332 were accounted for with the loss of nine steamers and nine minesweepers. Some 26 mines were also laid off the west coast of Ireland, but did no damage, except in one case where the villagers mistook one which had drifted ashore for a new sort of cask of liquor and tried to open it, with the loss of nine lives. Off the west coast of Scotland, out of 130 mines cleverly laid by the U80 off Mull, Stornoway, Coll, Skye and Harris, 76 were accounted for.
The year 1917 closed with a total of 3,989 enemy moored mines swept up in home waters, at a cost of 170 Allied and neutral merchant ships sunk and 28 damaged. The whole outlook was more hopeful, for while enemy minelaying as compared with 1916 had more than doubled, the number of ships sunk had increased only from 161 to 170.
Abroad the voyage of the German raider “Wolf” (Capt. Karl Nerger) had given minesweepers work in many an unexpected spot. She left Germany on Nov. 30 1916, slipped through the blockade line and got safely out to sea. She was a ship which registered 6,000 tons and carried 458 mines besides an armament of four 6-in. guns. Her voyage lasted 15 months. Rounding Cape of Good Hope, she cruised in the Indian Ocean, then proceeded south of Australia to New Zealand and Fiji, and, returning by New Guinea, the Dutch East Indies and the Cape, reached Germany safely in March 1918. Her mines were found all over the globe. Her first group of 25 was laid off Dassen I. (Capetown) and her second of 29 on Jan. 18 off Cape Agulhas (S. Africa). The former were swept up by four whaling steamers commissioned for the purpose. In the Agulfyas field two vessels were lost and only seven mines swept up in 1917. On Feb. 15 1917 39 mines were laid off Colombo and 19 off Cape Comorin (Ceylon). One of her prizes, the “Turritella” (renamed “Iltis”), dropped some 25 off Aden, and a large group of 68 mines off Bombay was laid by one of the two ships. The Colombo group was swept up by six trawlers, with the loss of two large ships. The Aden group was dealt with by small harbour tugs manned by Somalis within two months of its location and with the loss of one ship. The large group off Bombay was attacked by local vessels manned by British officers and Lascars, and 51 of its mines were swept up by June with the loss of five steamers.
The “Wolf's” next mining exploit was in Australian seas, where she laid 14 mines off Gabo I., the S.E. point of Australia, between Melbourne and Sydney, with the loss of one steamer; this was followed by a cruise to New Zealand, where 15 mines were laid in Cook Strait, between North and South Is., and 17 off Three Kings I. in the extreme north. These were all dealt with by Australian and New Zealand naval forces. Her last effort consisted of no mines laid N.W. of the Andaman Is. (Indian Ocean) on Sept. 4 1917, which were not located in that year. Her mines were responsible for the loss of some 15 ships, and it was not till Jan. 15 1918 that definite news of her movements was received at the Admiralty.
But by 1918 the effect of improved British methods was telling heavily on the enemy. The toll of German losses and the difficulty of replacing trained personnel were seriously affecting her minelaying, and the total number of Allied and neutral merchant vessels lost by German mining fell to 27. Closer cooperation between the intelligence and minesweeping divisions, the rapid distribution of intelligence, the firmer control of shipping and the use of the “otter”—all contributed to this very marked decrease.
The Germans now began to concentrate their minelaying efforts in three special directions—the maintenance of a minefield off the Dutch coast directed against the Dutch convoys, the laying of a large semicircular barrage about 45 m. from the Forth aimed at the Grand Fleet, and attacks on the route of the Scandinavian convoys. The first took the form of a field laid off Ymuiden and the Maas containing some 400 mines, which was extended by the labours of two U-boat minelayers working continuously in this area. It was responsible for the loss of five destroyers and remained a source of grave danger, for minesweepers working there were exposed to sudden attacks from the Flanders coast. The barrage off the Forth met with no success. The mines were rapidly located (in two cases by paravanes) and swept up almost as soon as they were laid. The attacks on the Scandinavian convoy routes were equally unsuccessful. Some 90 mines were swept up with the loss of only one steamer.
In the Harwich area 265 mines were laid, of which 213 were accounted for, with the loss of five steamers and four minesweepers. The discovery of a mine off Walney I. (Lancashire) on March 8 led to special vigilance in that area, and when mines were laid in the Mersey the next night, a unit of paddlers, held in readiness for the emergency, was at work at once clearing the fairway and opened the port to traffic within 48 hours.
The introduction of a French pattern of scissors to cut through the mooring-wire of a mine was one of the developments of the later years of the war, though the difficulty of minesweeping did not lie in cutting the mine's mooring-wire when found but in finding the mine in a trackless expanse of water under all sorts of conditions of tide and weather.
A very considerable amount of minesweeping work in 1918 arose out of British minelaying. The mines in a portion of the northern barrage were laid too shallow and had to be swept up in the approaches to the Orkneys. The same fault was found in Dover barrage, where some 280 mines had to be swept up and a great increase in drifting mines was experienced. The Channel still continued to be visited occasionally, and in the Portsmouth area 44 mines were accounted for with the loss of two merchant ships and two minesweepers.
In the Mediterranean, the enemy had devised a mooring system for tideless waters which permitted of mines being laid in too fathoms, but the clear blue water lent itself to aircraft reconnaissance which, in concert with light-draught motor-vessels, made location easy. Thirty mines were destroyed off Malta during the year 1918 with the loss of one steamer. The minesweepers were largely manned by Maltese reservemen who displayed a gallant spirit and seamanlike competency in their work.
Long before the Armistice, British minesweeping had gained the mastery over German minelaying, and as soon as Ostend and Zeebrugge fell into British hands, the protective minefields round them were swept up. When the hour of the Armistice struck, a minesweeping force was waiting at the gate of the Dardanelles, and within 24 hours 600 British and enemy mines had been removed from the entrance and a passage cleared for the fleet to Constantinople.
A few words may be said as to the method of distributing information of mines. This was sent out in what were called, from their index letter, “Q” messages, which were priority messages going to all shore stations by land wire and to all forces at sea by Cleethorpes wireless station at regular intervals. Immediately a mine was discovered or swept up, the spot was buoyed and local traffic at once diverted or, if the mine was in the war channel, held up. As soon as tidal conditions permitted, the area was swept. The text of a “Q” message was sent by the senior officer to the Admiralty, and, after being checked by the Minesweeping Division, was at once sent out to all ships and stations, the average time from the discovery of a mine to the issue of information to ships at sea being about 11/4 hours.
The growth of the minesweeping service and the greatness of its task, performed largely by British fishermen, may be gathered from the following figures. At the Armistice the minesweeping forces in British home waters comprised no fast sweepers organized in 20 minesweeping flotillas, 52 hired paddlers, 412 trawlers, 142 drifters and 10 “Dance” minesweepers—a total of 726 vessels. The number of mines destroyed at home and abroad by British vessels during the war amounted to 23,873 (moored, 11,487; drifting, 12,386). The ships sunk and damaged by mines numbered 595. The number of minesweepers sunk or damaged was 214, in the following areas: Fleetsweepers, 5; Lerwick, 1; Kirkwall, 3; Cromarty, 3; Peterhead, 2; Granton, 9; Tyne, 6; Grimsby, 15; Lowestoft, 48; Harwich, 24; Nore, 15; Dover, 33; Portsmouth, 13; Portland, I; Plymouth, 3; Falmouth, 2; Bristol Channel, 6; Queenstown, 7; Belfast, 6; Clyde, 2; Stornoway, I; abroad, 9.
Minelaying.—Minelaying played a very important part in the later years of the World War, but to form a true estimate of its value a careful distinction must be drawn between three factors essential to its success—its strategical use and function, the ​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.
In anticipation of the increased requirements some 12 modern light cruisers had been equipped for minelaying, and a batch of destroyers was fitted out to assist the “Abdiel” (“Tarpon,” “Legion,” “Telemachus,” “Ferret,” “Vanoc,” “Ariel,” “Vanquisher,” “Vehement,” “Venturous,” “Sandfly,” “Meteor”). These were to form the 20th Flotilla under Comm. Berwick Curtis, and to lay some 21,500 mines in the Bight in 1918. Meanwhile another big scheme had been propounded, involving nothing less than the closure of the northern exit of the North Sea to submarines, an area 230 m. in length with depths varying from 45 to 150 fathoms. The line first suggested was Aberdeen to Ekersund (Norway), but this was changed to Ork- neys to Udsire, to bring it more closely within the purview and under the protection of the Grand Fleet.
Fig. 1
Northern Barrage
1918
It was divided into three large areas: B, next the Orkneys, 45 m. long; A, in the centre, 135 m. long; and C, on the Norwegian side, 70 m. long. These required 65,700, 36,300 and 18,000 mines respectively, a total of 120,000, and it was intended to lay nine rows: three at an upper level of 80 ft., three at a middle level of 160 ft., and three at a lower level of 240 feet. A was laid by the U.S. navy; B, by the British; C, by both. An immense organization for transporting, filling, loading and laying the mines grew up round the work. The American base was at Inverness, under Rear-Adml. Joseph Strauss, with Capt. Reg. Belknap as chief-of-staff, and their mines were landed in the Kyles of Lochalsh near Skye and sent across by the Caledonian canal and by rail. The British mining base was at Grangemouth in the upper reaches of the Forth, under Rear-Adml. Lewis Clinton Baker, with Capt. Lockhart Leith as chief-of-staff.
The first mine was laid on March 3 1918, and on May 26 the American squadron (Mine Squadron I.) arrived at Invergordon to take part in the work. It was under Capt. Reg. Belknap and consisted of the U.S.S. “San Francisco” (Flag-Capt. H.V. Butler), “Baltimore” (Capt. A.W. Marshall), “Roanoke” (Capt. C. D. Stearns), “Housatonic” (Capt. J. W. Greenslade), “Canandaigua” (Capt. W. H. Reynolds), “Canonicus” (Capt. T. L. Johnson), “Quinnebaug” (Comm. D. P. Mannix), “Saranac” (Capt. Sinclair Gannon), “Shawmut” (Capt. W. T. Cluverius) and “Aroostook” (Capt. J. H. Tomb), with a total capacity of 5,530 mines. Some 57,000 mines were laid during the next five months by the U.S. squadron, escorted on their expeditions by British and American warships. The mine was of American design (see fig. 2), carrying 300 Ib. of T.N.T. and weighing with the sinker 1,400 lb. Antennae 70 ft. long (reduced to 35 ft.) rose from it, which fired the mine if touched by a ship. It was moored by a 3/8-in. wire cable, and attached to the sinker or anchor was a 90-lb. plummet on a reel of 1/8-in. steel wire, carefully measured to the length that the mine was to lie below the surface (160 ft., for instance, at the middle level). The mine was
Fig. 2
attached to the sinker, and, as it dropped from the steel rails astern, floated for a time. The plummet was released and ran out to the length of its cord, when it was brought up with a jerk. This released the mine from the sinker, which sank slowly with the mine cable running out. When .the plummet touched bot- tom, the cord slackened, releasing a clamp which clamped the cable, and the sinker now pulled the mine down with it to the proper depth.
Difficulties were encountered as the work proceeded. A proportion of mines (about 5%) exploded prematurely, and a number of mines in the British area were laid_ at less than the prescribed depth of 65 ft., which led to the sinking of the British sloop “Gaillardia” on March 22 1918. It was decided to sweep up the mines in the British portion, and when relaid a large gap was left off the Orkney coast to ensure a safe passage for the fleet. The work of laying this field was one of the great achievements of the war, and the accuracy of position required was facilitated by the use of the “taut"-wire method introduced by Vice-Adml. Sir Henry Oliver, in which the distance run was measured by fine piano-wire reeling out from I4o-m. spools. To prevent defective mines setting off others, the distance between lines was increased from 150 to 300 ft., and the rows increased to 10 at the upper level, 4 at the middle and 4 at the lower. The work of the American squadron marked a great step in minelaying, and it was no unusual feat for a single ship to lay a line of 860 mines covering 43 m. in 35 hours.
It must not be supposed that the whole of the water available for a submarine was effectively covered by this field, but the danger of the passage was greatly increased. In July the mine- field began to take its toll, and two German submarines were damaged in it, though they -managed to get home. They now began to creep past in Norwegian waters, but the Norwegians closed them to both belligerents by minefields of their own. This barrage must be regarded as a colossal attempt to solve the submarine problem, and as it was barely completed by the Armistice a comprehensive judgment of it is hardly possible. It showed every sign of success, and in September and October at least four German submarines (including U92 Sept. 9, UB104 Sept. 19, U156 Sept. 25, U102 probably, UB127 probably, UB123 Oct. 19) were lost in it, with a proportionate effect on the moral of their officers and men who saw their last means of exit closing before their eyes. The United States laid 56,571 mines in it, and the British 13,546.
In the south the old cross-Channel mine-net barrage had been abandoned early in the year, and Rear-Adml. Sir Roger Keyes' efforts were concentrated on the Folkestone to Gris Nez barrage, where 9,570 mines were laid with conspicuous success. Nine submarines were lost in it (U109, UB38, UB58, UB33, UB55, UB31, UC38, UC64, UB103), and the High Sea Fleet flotillas abandoned the Dover route early in the year.
The mining of the Bight went steadily on, performed by the 2Oth Flotilla under Comm. Berwick Curtis and the minelaying submarines. On March 27 the “Abdiel,” in company with the “Legion,” “Telemachus,” “Vanquisher,” “Ariel,” and “Ferret,” were laying a field 70 m. N.W. of Heligoland when they came on three outpost vessels, which they sank, bringing back 72 prisoners. The 34, which left Harwich July 14 to lay a field off Vlieland, never returned. These operations led to the
Fig. 3
Dover Barrage
1918
destruction tion of a number of minesweepers and torpedo craft, and though only one or two German submarines were lost on the mines their movements were undoubtedly seriously hampered.
In July the Germans suddenly began laying large protective minefields close to the Dutch line of lights, which resulted in the loss of the "Vehement" and "Ariel" on Aug. 1 and led to a great reduction in British mining in the Bight in the last three months of the war. The dangers of the Bight led to an increased use of the Cattegat by German submarines, and opened an excellent opportunity for deep mines in that area. A field was laid off the Skaw in February, and another in April off Lesso, which evidently caused considerable anxiety in Germany, but the work in this area was sporadic and did not form part of a coherent plan. Controlled minefields (that is, fields fired by instrumental means from a post in the vicinity on the passage of a submarine over them) were now being developed, and three submarines succumbed to them in 1918 (UC11, Harwich, June 26; UB109, Folkestone, Aug. 19; UB116, Scapa Flow, Oct. 28).
A large protective minefield of three deep and three shallow lines holding some 9,000 mines was laid in August and Septem- ber off the coast of Yorkshire and Durham, where submarines were particularly troublesome.
Minelaying by the end of the war had developed into one of the most important operations, and, favoured by geographical conditions, played a very important part in later British strategy, being an indispensable feature of the war against the submarine. The enormous number of mines used can be gathered from the fact that in the large minefields in home waters alone, there were some 34,300 mines laid in the Dover area and Narrows of the North Sea (including 9,500 in the Sir Roger Keyes' Folkestone to Gris Nez barrage); the Bight absorbed some 43,000 and the Northern barrage 70,117. There can be little doubt that too little importance was attached to the mine in British pre-war views on naval strategy. There was too great a tendency in those days to interpret war at sea wholly in terms of hitting a target at long ranges with a heavy gun. No modern battleship was sunk in this way, and of the various classes of British ships lost during the war, fewer were sunk by guns than by mines—namely 5 battleships out of 13 (38%), no battle cruisers out of 3, i cruiser out of 13 (7⋅7%), 2 light cruisers out of 12 (16⋅5%), 5 sloops out of 18 (28%), 20 destroyers out of 64 (31%), 4 submarines out of 54 (7⋅5%). In the destruction of German submarines they played a more important part. Of 200 submarines the loss of 43 (or 21⋅4%) was due to mines, and as one-fifth of those unknown (4 out of 17) may be attributed to the same cause it may be accepted that 23% of German submarine losses were due to British mines.  (A. C. D.)