This essay is first prize winner from the 2018 CNO Naval History Essay Contest in the Professional Historian category. The content of the original essay has been copyedited prior to publication.
Anti-access is often considered only as a form of sea denial for coastal defence. Yet it can work the opposite 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 is already restricted by geography. Anti-access operations can thus 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 the First World War is one of the best examples of such an effort. By further constraining Germany’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 defence more than 100 miles seaward. The requirement for continuous minesweeping operations and their protection close to the coast and at long distances steadily wore down the High Sea Fleet and limited its capacity to conduct other operations.
The British were, however, slow to embark on an effective mining campaign. Financial constraints and a lack of priority had brought mine development to an effective halt by 1914.[footnote:footnote0] 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 were also inadequate. Defensive mines laid in the English Channel dragged several miles within a few days—something those responsible for mine design had fully expected.[footnote:footnote1]
British mine development was poorly managed for much of the war. Too much time was spent trying to fix unsatisfactory models. Only when the British decided to copy the much more reliable German contact mine was a solution found.[footnote:footnote2] Even then, they wasted time trying to improve the original design. 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.[footnote:footnote3]
The rules of mine warfare were also a restraint. In 1907, the Eighth Hague Convention had prohibited mine laying that had the “sole object of intercepting commercial shipping,” while it also required that mines which broke their moorings became inert.[footnote:footnote4] 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 SS 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.[footnote:footnote5] This was the start of an effort that included the battleship HMS Audacious amongst its early victims. Nevertheless, as Allied attempts to blockade Germany were soon the source of much neutral ill feeling, the British, at least early in the war, were cautious about deploying mines in areas that would claim neutral victims. They declared the North Sea a “military area” with effect from 5 November 1914, but more specific restrictions for the Bight were not issued until January 1917—and even these were modified to meet neutral concerns.[footnote:footnote6]
Another important constraint on British offensive operations was defensive minelaying against U-boats. This 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 whether this result justified the enormous effort involved. The second element, minefields in the English Channel, eventually proved to be a vital complement to the offensive campaign in the Heligoland Bight, but at a price. The Channel consumed the majority of 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 very end of 1917. When they did, the effect was immediate. At least 10 U-boats fell victim to the barrage laid between Folkestone and Cape Gris Nez between January and June 1918.[footnote:footnote7]
The British had rejected the idea of offensive mining in the Heligoland Bight shortly after the start of the war,[footnote:footnote8] but the Commander-in-Chief of the Grand Fleet, Admiral Jellicoe, became an early convert, partly through his increasing fear of the U-boat threat, but also as protection against raids by the High Sea Fleet.[footnote:footnote9] Minefields in the Bight would create problems for German units as they attempted to deploy and help provide warning to the British of a major sortie. Furthermore, laying the fields well offshore would not only increase the burden for the German minesweepers, but expose them to “continual swoops” by British light forces.[footnote:footnote10] In this, Jellicoe’s views aligned with the evolving ideas of the First Sea Lord, “Jacky” Fisher.[footnote:footnote11]
The first offensive operation took place in January 1915, with a field laid on the Amrum Bank, but the old minelayers were not up to the job.[footnote:footnote12] 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 developing a very low opinion as to their lethality. The resignation of Lord 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 availability and quality meant the offensive effort in the Bight in 1916 was limited to only seventeen small fields and 1,782 mines.[footnote:footnote13]
Despite this, these operations achieved disproportionate results. Submarine fields were the key factor. The British had suffered enough from minelaying U-boats to realise the effect of a handful of mines laid in a channel that had only recently 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 were soon 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.
Meanwhile, the British had internal debates about offensive minelaying. Many officers worried about its effect on other offensive operations. This remained an issue until the very end. 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.”[footnote:footnote14] Several mine lays were cancelled because of the Grand Fleet’s concerns,[footnote:footnote15] while the British conducted their own minesweeping operations in the Bight’s northern approaches to ensure freedom of manoeuvre. 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, allowing use of the area for further operations—which could include reseeding the field. Although the British continued with this technique to the end, the plugs proved unreliable and there were fears at least one minelaying unit fell victim to a mine from an old field that was still active.[footnote:footnote16]
While they struggled to produce enough effective weapons, the British realised 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 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 SMS 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 initially had a schizophrenic existence. Before each mining operation, part of their armament was disembarked before the mines could be loaded. On return to harbour, guns and torpedo tubes were reinstalled, bringing the comment, “We never quite knew whether we were a destroyer or a minelayer.”[footnote:footnote17] Recognition of the inefficiency brought the establishment of a destroyer flotilla tasked only with offensive minelaying in February 1918.
Specialising 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 significant inherent uncertainties, as well as the new systems which provided a much greater level of fidelity. While most units could not be sure of their position within five nautical miles after eight hours out of sight of land,[footnote:footnote18]experienced minelayers usually did much better. Introduction of the taut wire measuring system, by which wire paid out under strain provided an accurate record of distance run, was a big help. In 1918, a minelayer managed a run of 122 miles without breaking the wire.[footnote:footnote19]
The British operational concept for the Heligoland Bight, which finally matured in 1917, depended upon 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.[footnote:footnote20] The Germans soon felt the strain; they lost 33 surface units and at least six U-boats in the Bight that year.[footnote:footnote21] 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 were obviously suitable, but the number available was limited.[footnote:footnote22]
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 that protests from the Dutch and Danes would force the British to cancel their notice, but a compromise was rapidly agreed. This resulted in a new notice in July that reduced the declared area only marginally, while 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 required length of each German-swept channel by 20 to 25 miles. This was a serious problem. Admiral Scheer, commander of the High Sea Fleet, noted he “barely had sufficient ships to ascertain where mines were laid.”[footnote:footnote23]
Both sides were aware of the vital importance of knowing where the swept channels lay. The British—largely through signals intelligence—were generally successful at finding their location, but had to be circumspect in utilising the information, lest the Germans work out the source 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.
The British also laid dummy minefields. This was not only to divert enemy effort, but 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 concerned. A dummy field, however, still provided safe access for the enemy. The Germans, who did much of their sweeping at night and retained a low opinion of the effectiveness of British mines, did not recover many weapons. They did not realise 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 post-war information, they assessed the field concerned was a dummy.[footnote:footnote24] But it was not and the flotilla involved had been fortunate not to suffer the consequences. Its commander had disobeyed a direct order not to proceed east past the longitude which marked the field’s western boundary.[footnote:footnote25]
The British mining campaign was supplemented by a fourth activity in 1918—the Northern Barrage—deployed between Scotland and Norway. This was an American inspiration, supported by the British in the interest of coalition solidarity rather than belief in its utility. More than 70,000 mines were eventually laid—over 56,000 by American units.[footnote:footnote26] The hastily designed deep-water mines proved extremely 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 a period of six hours. This statistic was not exceptional.[footnote:footnote27] 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.[footnote:footnote28] 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 to mine their territorial waters closing an important gap, the system would have become increasingly effective had the war continued into 1919.
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 over 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.[footnote:footnote29] 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.[footnote:footnote30] 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 HMS Ariel struck mines and sank. One of the minelayers’ captains admitted they had been oblivious to the fact that “much of the water . . . considered innocuous, and . . . gaily careered over at 25 knots, teemed with” mines.[footnote:footnote31] The sinkings caused 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. HMS E45 was on her way to resume submarine mining when the armistice intervened, much to the relief of her captain.[footnote:footnote32] The final 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 which may still apply. Although under financial pressure before 1914, the Royal Navy was wrong to neglect a weapon which 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 consumed too many resources. The British were slow to realise, 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 less 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 anti-access 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.
Rear Admiral James Goldrick joined the Royal Australian Navy (RAN) as a 15-year-old cadet midshipman in 1974 and ended his full-time service in the RAN in 2012 as a two-star admiral. He completed a BA at University of New South Wales in Kensington and graduated from the RAN College at the end of 1978. In addition to sea service as a junior officer around the world in units of the RAN and the Royal Navy, he commanded HMA ships Cessnock and Sydney (twice), the Australian naval task group and the multinational maritime interception force in the Persian Gulf, the Australian Defence Force Academy (ADFA) (2003−2006 and 2011−2012), Australia’s interagency Border Protection Command (2006−2008), and the Australian Defence College (2008−2011). He is an adjunct professor at the University of New South Wales at Canberra (ADFA) and a member of the Naval Studies Group. He is also adjunct in the Strategic and Defence Studies Centre at the Australian National University (ANU), where he teaches at the Australian Command and Staff College and in other ANU programmes. He is a Professorial Fellow of the Australian National Centre for Ocean Resources (ANCORS) at the University of Wollongong. He was a visiting fellow at All Souls College, Oxford University in 2015. He is a member of Australia’s Defence Honours and Awards Appeals Tribunal and of the Defence Force Remuneration Tribunal. He was a member of the Minister’s Expert Panel supporting the development of the 2016 Australian Defence White Paper.
In addition to his BA, James Goldrick holds a Master of Letters degree from the University of New England. He was awarded a Doctorate of Letters (honoris causa) by the University of New South Wales in 2006. His books include: No Easy Answers: The Development of the Navies of India, Pakistan, Bangladesh and Sri Lanka and Before Jutland: The Naval War in Northern European Waters August 1914−February 1915, and, with Jack McCaffrie, Navies of South-East Asia: A Comparative Study. He has edited or contributed to more than 40 other volumes of naval history and maritime strategy, as well as to academic and professional journals, such as the British Naval Review, the U.S. Naval Institute Proceedings and IHS Navy International. He has just completed After Jutland: The Naval War in Northern European Waters June 1916−November 1918, which will be published by the Naval Institute Press in October.