The British experience contains lessons that still apply to modern-day mine warfare.
site way, cutting off a coastal state and preventing deployment of offensive forces into the open sea. This has great potential when an adversary’s access to the ocean already is restricted by geography. Antiaccess operations can be a vital contributor to achieving sea control, reducing the threat to shipping and releasing combatant forces for other tasks.
Britain’s mining campaign against Germany in the last years of World War I is one of the best examples of such an effort. By further constraining the country’s limited ability to reach open water, it placed the German Navy at an increasing disadvantage. Deploying minefields around the Heligoland Bight, the British threatened the safe transit of the U-boats on which the Germans depended for their campaign against Allied shipping. The need to protect their submarines extended the German requirement for coastal defense more than 100 miles seaward. The requirement for continuous minesweeping operations and the protection of minesweepers close to the coast and at long distances steadily wore down the High Sea Fleet and limited its capacity to conduct other operations.
A Slow Start
The British, however, were slow to embark on an effective mining campaign. Financial constraints and a lack of priority had brought mine development nearly to a halt by 1914.1 The handful of Royal Navy minelayers were old and slow converted cruisers, while the mines were in no better state. The triggering mechanisms were extremely unreliable; during an operation in October 1914, several mines blew up almost immediately after entering the water. Mooring systems also were inadequate. Defensive mines laid in the English Channel dragged several miles within a few days—something those responsible for mine design had fully expected.2
British mine development was poorly managed for much of the war. Only when the British decided to copy the more reliable German contact mine was a solution found.3 Mass production of the H2 mine (H for “Horned”) did not start until 1917, while the mine’s size required substantial modifications to the minelayers.4
The rules of mine warfare also were a restraint. In 1907, the Eighth Hague Convention prohibited minelaying that had the “sole object of intercepting commercial shipping,” while it also required that mines that broke their moorings become inert.5 Neither restriction proved realistic. The Germans, who had not subscribed to all the convention’s provisions, set the tone the day war started when the converted minelayer Königin Luise laid a field outside territorial waters in the southern North Sea. Although she was sunk by the British, her mines claimed the light cruiser HMS Amphion the next day.6 This was the start of an effort that included the battleship HMS Audacious among its early victims.
Nevertheless, as Allied attempts to blockade Germany soon were the source of ill feelings among neutral nations, the British were cautious about deploying mines in areas that could claim neutral victims. They declared the North Sea a “military area” with effect from 5 November 1914, but more specific restrictions for the Heligoland Bight were not issued until January 1917—and even these were modified to meet neutral concerns.7
Another constraint on British offensive operations was defensive minelaying against U-boats, which took two forms. The first was mining along the British coast to protect merchant shipping. Although five U-boats were sunk in these fields, it is doubtful this result justified the effort involved. The second element, minefields in the English Channel, eventually proved a vital complement to the offensive campaign in the Heligoland Bight, but at a price. The Channel consumed the majority of the British mine warfare effort between 1914 and 1918—significantly restricting the potential for offensive mining in 1915 and 1916—but even efficient mines represented a danger to transiting U-boats only if they were combined with effective patrols that forced the submarines to dive and enter the minefields. The British did not implement such a system until the end of 1917. When they did, the effect was immediate. At least ten U-boats fell victim to the barrage laid between Folkestone and Cape Gris Nez between January and June 1918.8
Offensive Mining Operations
The British had rejected the idea of offensive mining in the Heligoland Bight shortly after the start of the war, but the Commander-in-Chief of the Grand Fleet, Admiral John Jellicoe, became an early convert, partly because of his increasing fear of the U-boat threat, but also as protection against raids by the High Sea Fleet.9 Minefields in the Bight created problems for German units as they attempted to deploy and helped provide warning to the British of a major sortie. Further, laying the fields well offshore would increase the burden for German minesweepers while exposing them to “continual swoops” by British light forces.10 In this, Jellicoe’s views aligned with the evolving ideas of the First Sea Lord, “Jacky” Fisher.11
The first offensive operation took place in January 1915, with a field laid on the Amrum Bank in the northern Bight, but the old minelayers were not up to the job.12 Fast converted merchant ships replaced them in later months, and more than 4,000 mines were laid in the Bight by the end of 1915.
The mines, however, were largely ineffective. Drifting mines, the result of broken mooring wires, soon alerted the enemy, while the number of dud weapons contributed to the Germans’ low opinion of their lethality. The resignation of Fisher in early 1915 also meant a loss of impetus in the Admiralty. The combination of defensive requirements, a shortage of minelayers, and the problems with both mine availability and quality meant the offensive effort in the Bight in 1916 was limited to 17 small fields and 1,782 mines.13
Despite this, these operations achieved disproportionate results. Submarine fields were the key factor. The British had suffered enough from minelaying U-boats to realize the effect of a handful of mines laid in a channel that recently had been swept. They began to modify their own submarines accordingly. Although the first conversion was sunk by a German mine on her second operation, there soon were five E-class submarine minelayers. The Germans suffered the loss of only a few light craft in 1916, but the effect of the handful of inshore fields was that U-boats had to be escorted through swept channels. This placed a new burden on the High Sea Fleet.
Concerns and Shortcomings
Meanwhile, the British had internal debates about offensive minelaying. The commander of the Harwich Force of cruisers and destroyers complained in 1917 that “he could not be off the German coast with his light cruisers because he could not now get there.”14 Several mine lays were canceled because of Grand Fleet concerns, while the British conducted their own minesweeping operations in the Bight’s northern approaches to safeguard freedom of maneuver.15
One device to overcome the problem was the fit of soluble plugs to mines laid in offensive fields. The plugs were intended to dissolve after 38 days, causing the mines to sink and allowing use of the area for further operation—which could include reseeding the field. Although the British continued with this technique, the plugs proved unreliable, and there were fears at least one minelaying unit (submarine E34) fell victim to a mine from an old field that was still active.
As they struggled to produce enough effective weapons, the British realized that offensive mining required combatant units. High speed and covertness were more important than the ability to deploy large numbers of mines. The destroyer leader HMS Abdiel was the first combatant converted, initially as a tactical minelayer for the Grand Fleet. Although the field laid in the closing stages of the Battle of Jutland on 1 June 1916 claimed no victims, the battleship Ostfriesland was damaged by a mine Abdiel had put down a few weeks earlier.
Conversions of light cruisers and additional destroyers followed in 1917. The shortage of such vessels meant they had a schizophrenic existence. Before each mining operation, part of their armament was disembarked so the mines could be loaded. On return to harbor, guns and torpedo tubes were reinstalled, bringing the comment, “We never quite knew whether we were a destroyer or a minelayer.”16 Recognition of the inefficiency brought the establishment in February 1918 of a destroyer flotilla tasked only with offensive minelaying.
Specializing in mine warfare created expertise. Navigation was especially critical. Repeated operations allowed personnel to develop knowledge of the Heligoland Bight that provided a filter for formal position-finding methods that had inherent uncertainties, as well as the new systems that provided greater fidelity. While most units could not be sure of their position within five nautical miles after eight hours out of sight of land, experienced minelayers usually did much better.17 Introduction of the taut wire measuring system, by which wire paid out under strain provided an accurate record of distance run, was helpful. In 1918, a minelayer managed a run of 122 miles without breaking the wire.18
Heligoland Bight Offensive
Heligoland Bight, which finally matured in 1917, depended on a combination of offshore fields laid by surface ships and smaller inshore fields deployed from submarines. Although mine production was in high gear by late in the year, the number laid never approached the 65,000 to 70,000 of early estimates. The total for 1917 was 15,686; yet this was enough.19
The Germans were strained by the loss of 33 surface units and at least six U-boats in the Bight that year.20 Manning the U-boat fleet was draining the High Sea Fleet of its best junior leaders and technicians. Expanding the minesweeping force created new pressures. The work required a high degree of seamanship and experience in handling small craft. Fishermen obviously were suitable, but the number available was limited.21
The British made the problem even harder for the Germans with the extension on 25 June 1917 of their declared “Notified Mined Area” in the Heligoland Bight. The Germans hoped protests from the Dutch and Danes would force the British to cancel their notice, but they came to a compromise.
A new notice in July reduced the declared area marginally, and the Dutch set up a buoyed and lit shipping channel to the west. The markers proved very useful to the British in confirming their own positions before approaching the Bight. The July notice increased the length of each channel needing to be swept by the Germans by 20 to 25 miles. This was a serious problem. Admiral Reinhard Scheer, commander of the High Sea Fleet, noted he “barely had sufficient ships to ascertain where mines were laid.”22
Both sides were aware of the vital importance of knowing where the swept channels lay. The British, largely through signals intelligence, generally were successful at finding their source, but they had to be circumspect in using the information, lest the Germans work out the location of their compromise. The Germans suspected that their sweeping was being monitored by submarines. Although submarine reports were extremely useful, they could not substitute for the timelier—and more accurate—decryptions. So eager were the Germans to conceal the swept channel entrances, they abandoned the practice of meeting returning U-boats, diverting the latter to return home via the Kattegat off northeastern Denmark.
The British also laid dummy minefields. This was not only to divert enemy effort, but also to lull the Germans into a false sense of security. Once the existence of an enemy minefield was known, both sides often left mines in place if their location did not impede their own activity. The field thus became part of the defensive system of the protagonist. A dummy field, however, still provided the British safe access. The Germans, who did much of their sweeping at night and retained a low opinion of the effectiveness of British mines, did not bother to recover many weapons and so did not realize what the British were doing until after the war.
Even then, they drew some false conclusions. In one episode, the Germans were puzzled when a flotilla of Royal Navy destroyers went straight over a known British minefield to attack a group of minesweepers. With the benefit of postwar information, they assessed the field concerned was a dummy.23
The Northern Barrage
The British mining campaign was supplemented by a fourth activity in 1918—the Northern Barrage, deployed between Scotland and Norway. This was a U.S. inspiration supported by the British in the interest of coalition solidarity rather than belief in its utility. More than 70,000 mines were laid, more than 56,000 by U.S. units.24
The hastily designed deep-water mines proved unreliable. Premature detonations were a key problem; one escort reported after a September 1918 minelaying operation that it recorded an explosion every two minutes over six hours. This statistic was not exceptional.25
Whether the barrage was worthwhile is still debated. Estimates suggest six U-boats were sunk, with other units damaged, but the Germans continued to move through the area.26
Apart from the mine problems, the system lacked the extensive surface patrols that would force the U-boats to dive and risk the deep minefields. Nevertheless, with the Norwegian agreement allowing the Allies to mine their territorial waters closing an important gap, the system would have become increasingly effective had the war continued into 1919.
Germans Under Pressure
By early 1918, the Germans were hard pressed to keep even a single channel open in the Bight. The need for covering forces was demonstrated by the Second Battle of Heligoland Bight on 17 November 1917, when German minesweepers and their escorts succeeded in escaping from a British force with the loss of only one unit. Their withdrawal was supported by two battleships, confirming the need for heavy ships to protect the sweepers. This became the primary duty of the High Sea Fleet’s capital ships. In the spring, the Germans began to lay additional defensive minefields to protect the outer limits of the swept channels and more than 5,000 mines were deployed.
Mid-1918 brought new problems. The British became aware that the Kattegat was being employed by the U-boats as an alternative to the Bight. They began to lay mines in this area, as well as conducting attacks on the local German patrols. Although the Allied navies were hit hard by the influenza pandemic in April, a few weeks later the German minesweepers had so many sick they were hard put to remain operational.27
The Germans attempted to improve their situation at the end of July 1918, when Admiral Scheer directed that a new channel be cleared in the Bight. This was a massive operation, involving nine half-flotillas of minesweepers.28 Only one U-boat was available to use the channel immediately on its opening, but the passage remained undetected by the British until September.
Their additional minefields finally paid off for the Germans on 2 August. Eight ships of the 20th Flotilla ran into a minefield. Two destroyers, HMS Vehement and Ariel, struck mines and sank. The sinkings forced the British to rein in their offensive mining significantly. Between 2 August and the armistice on 11 November, only four surface sorties were conducted, all in outer areas of the Heligoland Bight.
The Germans, who still had many fields to clear and continued to suffer casualties, did not perceive that there had been a lull. Had the war continued, however, the tempo would have increased again. E45 was on her way to resume submarine mining when the armistice intervened, much to the relief of her captain.29 The last sortie of the High Sea Fleet provided a final demonstration of the importance of the British mining offensive. As the German ships sailed through the Bight to internment, the torpedo boat V30 struck a mine and sank.
The British experience contains several lessons that may still apply. Although under financial pressure before 1914, the Royal Navy was wrong to neglect a weapon that had real utility. The mine was not only for weaker powers; it was and remains a way of closing off a would-be aggressor like Germany from the world’s oceans and thus is a potential contributor to sea control. Had the British given mine development a high priority and managed it properly, they could have embarked on a successful offensive campaign at least 12 months earlier than they did.
Defensive mining had a vital role as well, but it consumed too many resources. The British were slow to realize, despite the success of the U-boat mines, that a handful of well-placed weapons could have disproportionate effects. The more effort the German Navy had to put into maintaining access to the open sea, the fewer resources it had for its own offensive operations. This became ever more apparent as 1917 gave way to 1918.
The British did not forget their experience when war returned in 1939, but neither did the Germans. They learned the lesson of the British antiaccess campaign and would not be enclosed again. Key to their strategy was the occupation of Denmark and Norway to overcome Germany’s geographic disadvantage. With these successful invasions and the fall of France, Britain suffered a defeat that would lead to the long and bitter conflict in the North Atlantic.
2. CAPT (later ADM) Philip Dumas, RN, Diary entries dated 2 and 3 October 1914, Dumas Papers, Imperial War Museum.
3. Norman Friedman, Naval Weapons of World War One (Barnsley: Seaforth, 2011), 365–66.
4. CAPT (later ADM Sir) Matthew Best, RN, Diary entry dated 30 December 1917, Best Papers, Liddle Collection, Leeds University.
5. “Laying of Automatic Submarine Contact Mines” (Hague, VIII), Convention signed at The Hague 18 October 1907, Articles 2 & 1, www.loc.gov/law/help/us-treaties/bevans/m-ust000001-0669.pdf.
6. James Goldrick, Before Jutland: The Naval War in Northern European Waters, August 1914–February 1915 (Annapolis, MD: Naval Institute Press, 2015), 85–87.
7. Naval Staff History, British Mining Operations 1939–1945, vol. I, Director of Naval Warfare, Ministry of Defence (March 1973), 18.
8. British Mining Operations, 39.
9. “Report of Conference on board HMS Iron Duke on 17th September 1914,” UK National Archives ADM 137/995. Jellicoe to Beatty, letter dated 4 June 1915, A. Temple Patterson (ed.) The Jellicoe Papers: Selections from the private and official correspondence of Admiral of the Fleet Earl Jellicoe of Scapa, vol. I, 1893–1916 (London: Navy Records Society, 1966), 166.
10. C-in-C Grand Fleet to Secretary of the Admiralty, letter dated 14 August 1915, A. Temple Patterson, The Jellicoe Papers, vol. I, 181.
11. Fisher to Churchill “Mine-Laying” aper dated 4 January 1915, Arthur J. Marder, Fear God and Dread Nought: The Correspondence of Admiral of the Fleet Lord Fisher of Kilverstone, vol. III, Restoration, Abdication and Last Years 1914-1920 (London: Jonathan Cape, 1959), 122–23. See also Fisher to Jellicoe, letter dated 12 January 1915, 128–29.
12. Goldrick, Before Jutland, 250.
13. Training and Staff Duties Division, Admiralty, Naval Staff Monograph (Historical) vol. XVIII, Home Waters—Part VII: December 1916 to April 1917 (May 1933), 107.
14. Charles à Court Repington, diary, entry of September 1917, cited in A. Temple Patterson, Tyrwhitt of the Harwich Force (London: Macdonald and Jane’s, 1973), 193.
15. Best, diary, entry dated 25 October 1917, Best Papers, Liddle Collection.
16. CAPT Taprell Dorling, RN, Endless Story: Destroyer Operations in the Great War (Barnsley: Seaforth, 2016), 374.
17. CDR L. Pitcairn-Jones, RN, “Navigation in War of 1914–1918,” RN Staff College Lecture 1938, Royal Naval Historical Branch, 12.
18. CAPT Reginald Belknap, RN, “Submarine Mines in War,” Belknap Papers, 12.
19. British Mining Operations, 19.
20. ADM Reinhard Scheer, IGN, Germany’s High Sea Fleet in the World War (London: Cassell, 1920), 199–201. See also: Gerhard P. Groos, Der Krieg zur See 1914–1918: Der Krieg in der Nordsee, vol. 7, Vom Summer 1917 bis zum Kriegsende 1918 (Hamburg: E. S. Mittler, 2006), 47–74.
21. Hugo von Waldeyer-Hartz, Admiral von Hipper (London: Rich & Cowan, 1933), 230–31.
22. Scheer, Germany’s High Sea Fleet, 290, 289.
23. RADM Eberhard Wolfram, “Dummy Mines,” Marine Rundschau (January 1934), US Naval War College Historical Collection.
24. CAPT R. R. Belknap, USN, “The Northern Mine Barrage,” 26 January 1919, Belknap Papers, U.S. Naval War College Historical Collection.
25. David Stevens, In all Respects Ready: Australia’s Navy in World War One (Melbourne: Oxford University Press, 2014), 350; and Mine Squadron One, “Combined Mining Report,” dated 26 October 1918, Belknap Papers, U.S. Naval War College Historical Collection.
26. Robert M. Grant, U-boat Intelligence 1914-1918 (Hamden CT: Archon, 1969), 101–09. Grant estimates six boats sunk. British Mining Operations lists five, but leaves out U92, whose wreck was found in 2007, confirming her loss in the barrage.
27. Von Waldeyer-Hartz, Admiral von Hipper, 231–32. See also Groos, Der Krieg in der Nordsee, vol. 7, 351-352.
28. Groos, Der Krieg in der Nordsee, vol. 7, 360–61.
29. CAPT R. W. Blacklock, RN, Memoirs, 80–81, Blacklock Papers, Liddle Collection, Leeds University.