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 38-in. wire cable, and attached to the sinker or anchor was a 90-lb. plummet on a reel of 18-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 destruc-
