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North Sea Mine Barrage 1918 in the Great War - The Wartime Memories Project -

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North Sea Mine Barrage 1918

1st June 1918 North Sea Mine Barrage 1918  The North Sea Mine Barrage, also known as the Northern Barrage, was a large minefield laid easterly from the Orkneys to Norway by the United States Navy (assisted by the Royal Navy) during World War I. The objective was to inhibit the movement of U-boats from bases in Germany to the Atlantic shipping lanes bringing supplies to the British Isles. Rear Admiral Lewis Clinton-Baker, commanding the Royal Navy minelaying force at the time, described the barrage as the "biggest mine planting stunt in the world's history."

The idea of a mine barrage across the North Sea was first proposed in the summer of 1916 by Admiral Reginald Bacon and was agreed at the Allied Naval Conference on 5 September 1917. The Royal Navy and, in particular Admiral Beatty as Commander in Chief of the Grand Fleet, was skeptical about the value of the operation and did not feel it justified the large logistical and manufacturing commitment required. A minefield across the North Sea would require mining water 900 feet deep while no previous minefield had been established in waters more than 300 ft deep. A minefield across the North Sea had been estimated to require 400,000 conventional anchored mines. An "antenna" mine developed in July 1917 was effective at the assumed maximum submarine depth of 200 ft and 100,000 of these new Mk 6 mines would be adequate to form the North Sea mine barrage. The United States was altogether more enthusiastic about the operation as the loss of trans-Atlantic shipping was a major domestic concern. This plan allowed the United States to play an active part in tackling this while playing to their industrial strength and with minimal risk of American casualties. Assistant Secretary of the Navy Franklin D. Roosevelt appealed directly to President Woodrow Wilson to overcome opposition to the project from Vice Admiral William Sims, who commanded all United States naval forces in Europe. The U.S. Navy tendered an order for the Mk 6 mines in October 1917 with 80,000,000 ft of steel wire rope required to moor the mines to the seabed. Project spending of $40 million was shared among 140 manufacturing contractors and over 400 sub-contractors. All mine components other than wire rope, explosives, and detonating circuitry were manufactured by Detroit automobile firms. Eight civilian steamships were converted to minelayers and another 24 mine carrying freighters, sailing at a rate of two or three per week, were required to transport manufactured mine components to assembly depots in Scotland.


The objective was to prevent U-boats from operating in the North Atlantic and preying on trans-Atlantic shipping. A similar barrage had already been placed across the English Channel, which had resulted in U-boats diverting north around Scotland. The North Sea Mine Barrage was intended to close this alternative route and it also made it hard for the U-boats to get supplies.

Success of the barrage

Supply problems and technical difficulties caused some delays but laying got under way in June 1918 and continued over the next five months. Planned additional minelaying excursions to complete the barrage were cancelled when the approaching end of hostilities was recognized upon completion of the thirteenth minelaying excursion on 26 October 1918. The design of the minefield meant there was a theoretical 66% chance of a surfaced U-boat triggering a mine and a 33% chance for a submerged U-boat. On the basis of the number of effective mines observed while sweeping the barrage, the actual odds were assessed at being closer to 20% for a surfaced U-boat and 10% for a submerged one. As the final mines were laid only a matter of days before the end of World War I, it is impossible to assess the success of the plan. Some contend the minefield was a major cause of the declining morale of the Imperial German Navy through the final months of the war, while others suggest Germany easily swept safe channels through the large, unguarded minefield. The official statistics on lost German submarines compiled on 1 March 1919 credited the North Sea mine barrage with the certain destruction of four U-boats, probable destruction of two more, and possible destruction of another two.

  • Possible losses in minefields.
  • 19 August 1918 SM UB-12 unknown - possibly sunk by the North Sea mine barrage
  • 9 September 1918 SM U-92 presumed sunk by the North Sea mine barrage area B (confirmed in 2007)
  • 9 September 1918 SM UB-127 sunk by the North Sea mine barrage area B
  • 25 September 1918 SM U-156 sunk by the North Sea mine barrage area A
  • September 1918 SM U-102 presumed sunk by the North Sea mine barrage area B (confirmed in 2006)
  • 19 September 1918 SM UB-104 sunk by the North Sea mine barrage area B
  • 20 September 1918 SM UB-113 unknown - possibly sunk by the North Sea mine barrage
  • 18 October 1918 SM UB-123 sunk by the North Sea mine barrage area A

Eight more boats were known to have been damaged by the mines and some Admiralty personnel assumed the field might be responsible for five more U-boats which disappeared without explanation.


United States participation in the minesweeping effort was overseen by Rear Admiral Strauss aboard the repair ship Blackhawk from which he had commanded the minelaying operation. Tugs Patapsco and Patuxent towed Admiralty wooden sailing smacks Red Rose and Red Fern out to conduct the first trial sweep in December. Sweeping was accomplished by suspending a serrated wire between two ships on a parallel course. While held underwater by planing devices called "kites", the wire would foul the cables suspending the buoyant mines above their anchors. If the serrated wire parted the mine mooring cable, the mine would bob to the surface to be destroyed by gunfire. The smacks swept and destroyed six mines before winter weather halted further work at sea. The winter was spent testing an electrical protective device to reduce the risk of sweeping the antenna mines with steel-hulled ships. Patapsco and Patuxent tested the protective device by sweeping 39 mines in March. Royal Navy minesweeping efforts involved 421 vessels manned by 600 officers and 15,000 men from 1 April to 30 November 1919. Twelve Lapwing class minesweepers and 18 submarine chasers were available for the first routine sweep of the United States minesweepers on 29 April 1919. After the first sweep took two days to clear 221 mines, Strauss requested more ships in the hope of clearing the mine barrage that summer. Twenty Admiralty trawlers with American crews, 16 more Lapwing class minesweepers, and another repair ship Panther were assigned to his command. Common difficulties with the sweeping procedure involved mine cables becoming entangled in the kites attached to the sweeping wires. Sweeping gear was often lost if the mine detonated and cut the sweeping cables. Approximately one third of the ships were damaged by exploding mines. Strauss was recognized as a Knight Commander of St Michael and St George for his efforts, but doubts about the effectiveness of the minesweeping effort persisted into the 21st century.

Postwar consequences

As 1919 drew to a close, the onset of winter forced the suspension of sweeping for moored buoyant mines, but the Royal Navy resumed minesweeping operations the following spring, continuing to clear sunken mines from fishing grounds and maintaining a destroyer patrol to track down mines that had broken free of their moorings and gone adrift. Losses of civilian ships to North Sea mines continued; the origin of the mine in these cases was often difficult to determine. In 1919, twenty crewmen drowned when the Swedish steamship Hollander sank, minutes after striking a mine in October and the steamer Kerwood struck a mine and sank on 1 December 1919.

John Doran

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