The War at Sea

The War at Sea

The War at Sea: Overview

The First World War was the first truly global conflict and the war at sea was no exception. In fact it was the campaigns at sea that took the war to the most remote corners of the globe. Actions took place as far away as the Pacific and Indian Oceans, although the most significant actions were primarily fought between British and German ships. 

Early in the war, Germany began attacking British trade routes in a bid to force the army to despatch forces to its Imperial colonies – forces the army could not afford to remove from the Western Front. In late 1914, German raiders in the Pacific inflicted the first defeat for a hundred years on the Royal Navy at the Battle of Coronel and a solitary German cruiser caused chaos in the Indian Ocean, but by early 1915, Germany’s overseas squadrons had been defeated.

In the North Sea, the Imperial German Navy’s High Seas Fleet and the Royal Navy’s Grand Fleet constantly sought to force a battle on their own terms that could end the war. Britain also tried to blockade Germany, but could not stop the High Seas Fleet from making incursions into British waters in an effort to lure the Grand Fleet into a battle nearer German ports. The anticipated battle finally came in spring 1916, when the largest ever battleship fleet action took place off Jutland. Although the High Seas Fleet dealt a severe blow to the Grand Fleet, the British were able to maintain their blockade and dominance of the North Sea until the end of the war.

Germany had plans for a blockade of its own, and saw its true strength in submarines. The Imperial German Navy adopted a policy of unrestricted submarine warfare and U-boats were responsible for so many merchant ship losses that Britain was soon at risk of being starved out of the war. However, an overhaul of the Dover Patrol and a barrage across the straits stopped the U-boats from taking the most direct route to the English Channel. This, combined with improved anti-submarine technology soon turned the tables.

By late 1918, the worsening effect of the British blockade on the German populace and a wildly optimistic plan for a fleet attack in the North Sea drove German sailors to mutiny. The revolution quickly spread and the Kaiser was forced to abdicate, precipitating the end of the war.[i]

War Around the World

The first year of the war was dominated by ‘cruiser warfare’. Isolated German warships based at foreign ports in Germany’s young empire began to attack British and Empire merchant ships around the world. SMS Emden, a German cruiser, was one such ship, which successfully captured or sank 26 ships in the Indian Ocean before it was caught and defeated by the Australian cruiser HMAS Sydney in November 1914. In the Pacific Ocean, a small squadron of vessels under Admiral Graf von Spee defeated a British Squadron off Chile, sinking two British cruisers with all hands. It was the first defeat suffered by the Royal Navy in 100 years and 1,600 men were lost. Already the war at sea had produced a disaster on a worse scale than the loss of the Titanic two years earlier. The Royal Navy, shocked and stunned by the defeat, send a powerful force to find von Spee’s squadron. Less than a month later, at the Falkland Islands, the German force was annihilated with the loss of 1,900 men.

Germany’s cruisers had been mopped up by mid-1915, but closer to home, the maritime war was taking on new significance. Few people realise that Gallipoli began as a naval effort and at first there wasn’t a single soldier involved. It was an attempt by the Royal and French navies to force the Dardanelles Passage so that they could reach Constantinople and force Turkey out of the war, thereby easing pressure on the European theatre. It was only the fleet’s failure in the face of forts and mines that led to the army being sent in, with the aim of neutralising the forts. Churchill believed the eventual failure of the campaign was crucial to lengthening the war. After the war he wrote: “The bones of the six million people who lay buried on battlefields were not defeated by enemy fire at all. They were destroyed entirely by 26 iron balls, which lay anchored to wire ropes under the surface of the Dardanelles strait.”

But it was in the waters around Britain that both sides fought to shorten the war through differing, yet oddly similar strategies. Not only were these efforts crucial to the ending of the war in 1918, but they brought the war into British territory in a way more devastating than any war of the previous 300 years.

War at Home

The war in home waters was complicated not only by strategic and tactical factors (such as the use of submarines, torpedoes and mines) and the dangers of operating in narrow straits and close to shore, but by complex political factors that threatened to incur the wrath of neutral nations should they be challenged. In 1909, all of the world’s major maritime powers had agreed a set of rules to govern maritime actions in the event of a war. In essence, the Declaration of London sought to protect civilian merchant traffic and the right to free trade across the world’s seas, especially between neutral nations and belligerents. Most nations had codified the rules and written them into their own constitutions. However, only the United States had actually ratified the declaration and so were bound to abide by it.

Germany and Austro-Hungary declared that they would operate according to the declaration’s rules as long as other nations did so. On 20th August 1914, the British government and the Royal Navy declared that they would also, but with certain modifications. In fact these modifications began a series of usurps of the declaration that would culminate in its almost total abandonment by 1917.

The declaration prevented nations from imposing a distant blockade to disrupt the travel of merchant shipping to and from a nation’s ports. In essence it was considered illegal to interfere with shipping and trade at sea – such actions could only be taken in a close blockade, around the enemy’s own ports. The Royal Navy’s blockade that commenced in August directly violated this when it essentially sealed the northern and southern entries to the North Sea. Maritime traffic was required to enter the North Sea through the Dover Straits where it could easily be intercepted by the Royal Navy and inspected for contraband. This contraband was material that might be used for war, such as arms, artillery and ammunition. Even if it was bound for the neutral countries of Denmark, Norway or The Netherlands, this material could be seized by the British.

In September the definition of contraband was extended to include materials that might be used to help make weapons for war. So steel, rubber or iron ore could also be seized. Finally in March 1915, the British government extended the definition of contraband to include materials for the civil population of Germany, including foodstuffs and the products required to grow food (such as fertilizers). This was an almost total violation of the Declaration of London, but there can be little doubt that it was one of the most important elements in winning the war.

The blockade also set up a battleground in the North Sea, with the Royal Navy operating from its base at Scapa Flow, whilst the German High Seas Fleet remained in its ports on the north coast of Germany. Throughout 1914 and 1915, both sides tried to instigate an engagement where they could gain the upper hand, by bring their full fleet to bear on a smaller force and wearing down the enemy piecemeal, or enticing the enemy fleet through a minefield or into range of a submarine flotilla. Several small skirmishes occurred as each side tried to create the ideal battle.

Eventually this led to the confrontation at Jutland, the largest battleship encounter in history.[ii] Despite its scale, the battle was somewhat inconclusive. Tactically the Germans won by inflicting more casualties on the Royal Navy than the British did on the German fleet. But strategically the status quo was maintained and Britain maintained command of the North Sea. Crucially, Germany was unable to break the blockade.

But Germany had a different weapon it could use to break the deadlock, one that ironically neither side had thought much of before the war.

Breaking the Blockade

The submarine was a comparatively new weapon and yet to prove itself in war. Neither the British nor the Germans had particularly great expectations of them when war broke out – it was thought they may be useful scouts for the fleets or as patrol vessels, but not as a major instrument of war.

That changed in September 1914. The German Imperial Navy demonstrated the potential of new technology when one U-boat (U-9) sank three British cruisers (HogueAbukir and Cressy) in just over an hour. The Royal Navy, caught on the back foot, was unprepared for this new form of warfare. Whilst their fleet dispersed to the west side of Scotland whilst Scapa was suitably defended, Germany quietly began building more U-boats for the coming years.

Germany first tried to conduct a commerce war on British merchant shipping in 1915. In contrast to the later campaign, this was not intended to completely destroy British merchant traffic. Rather, the aim was to put pressure on the British government to lift its own blockade which, it was believed, would take six weeks. In February of that year, the waters around Britain were declared a war zone in which any enemy merchant ship was liable to be attacked. This was a restricted campaign to damage Britain’s merchant trade, but was not meant as a terror attack on civilians. The crews of the vessels attacked were to be given sufficient warning and time to abandon ship and reach safety, according to the rules of war and the Declaration of London.

The larger U-boat fleets prowled around the North Sea and English Channel shipping lanes. Both the Mercantile Marine and the Royal Navy were unprepared for this form of warfare and could do little to interfere with the U-boats unless they caught them on the surface. But the campaign was not without problems. The sinking of the Lusitaniaand the Arabic liners, coupled with other attacks that breached the rules of war, brought intense political pressure on Germany from other nations, particularly the United States which was still neutral. In August the campaign was abandoned, having already failed to force Britain to lift its blockade in six weeks.

By 1916, Germany came to realise that the U-boat was still the best weapon to fight the blockade.  In March a new restricted campaign was begun and once more flotillas of submarines patrolled around Britain’s coast.[iii] Once again merchant ships losses increased, but again the over enthusiastic actions of some U-boat captains created political pressure on Germany. As the passenger ship Sussex crossed from Folkestone to Dieppe in March, she was torpedoed without warning by U-29. Although the ship didn’t sink, over 50 men, women and children were killed in the explosion. The outrage in the United States forced Germany to issue the Sussex Pledge, a promise not to attack passenger ships or merchant ships without armaments at all, and that any civilian vessel that was attacked must be given time for the crew to escape. The pledge essentially ended the 1916 campaign in May.

The German admiralty faced a dilemma by the end of the year. Increasing number of merchant ships were being armed for their own protection, but this made it dangerous for a U-boat to surface and warn the crew to abandon ship before attacking. In any event, surfacing before an attack negated the major advantage of a submarine – the ability to surprise its enemy. These factors, along with the failure to break the British blockade with the previous campaigns or at Jutland led to a new strategy being approved in 1917.

Proponents of U-boat warfare believed that, with sufficient numbers of submarines available, a sustained campaign against merchant shipping could destroy the British Mercantile Marine in six months. Such a blow would create an untenable situation in Britain, which relied on maritime trade in order to survive.[iv] Such a campaign would need to have a no holds-barred approach; political considerations would need to be ignored but, it was hoped, would be rendered irrelevant by the speed of Britain’s downfall and eventual capitulation.

Accordingly, on the 1st February 1917, a wider expanse of sea around Britain was declared a war zone within which any vessel, military, civilian, belligerent or neutral, was at risk of attack without warning. Only two days later the United States severed all diplomatic relations with Germany. In April, in response to the campaign and the infamous Zimmerman Telegram (a diplomatic entreaty from Germany to Mexico pledging to support them in the event of a war with the States), the United States declared war.

The race was now on to destroy British merchant shipping faster than the Allies could build it and before the British blockade completely starved Germany. Admiral Beatty commented that "The real crux lies in whether we blockade the enemy to his knees, or whether he does the same to us."

Merchant ship losses increased dramatically, particularly in the seas around Britain. For a while it looked like the campaign may work; losses quickly outstripped the building programme and led the First Sea Lord Admiral Jellicoe to warn that Britain could not pursue the war into 1918 unless the situation was improved.

The eventual victory over the U-boat was owed to several factors but some were more important than others. For years the Royal Navy had been improving its anti-U-boat weapons and now the depth charge had become a proficient weapon. The entry of the United States into the war opened up a wealth of industrial power that enabled a sustained shipbuilding programme to be maintained and brought numerous warships into home waters. But perhaps the most important factor was the use of convoys.

Although it may seem obvious in the light of the Second World War that convoys enabled merchant ships to be better protected, that was not the opinion of the Admiralty in the First World War. From 1914 to 1917, merchant ships had sailed the routes and timetables they had always done; the only nod to the war being the extinguishing of lights, the fitting of a deck gun and perhaps the occasional escort. The idea of gathering ships into convoys seemed to play into the hands of the U-boats; enabling them to sink a collection of vessels all neatly lined up for their torpedoes. In fact the opposite was true. A scattering of a hundred ships bustling around the English Channel would mean that a U-boat was bound to stumble over a target sooner or later. But if those 100 ships were gathered into five convoys, then the U-boat would be far less likely to encounter one. Twenty ships in close company are no easier to spot at sea than two; reducing the number of isolated ships crossing the channel reduced the chances of them being found.

Grouping vessels in a convoy also made it easier to defend them. A few Royal Navy warships could protect dozens of vessels in this way and the results quickly spoke for themselves. Rear Admiral William Jameson observed that “About one in every ten ships sailing alone was sunk; for ships in convoy it was between one and two in a hundred.”[v]

Losses steadily fell into 1918 and, although the campaign continued until the end of the war, it had shot its bolt: the U-boats steadily became less and less effective. At the same time, the Allied blockade was making more of an impact as time passed. Starved of imports and slowly running out of the supplies needed to grow its own resources, the German population was slowly starving and the armed forces were running out of war materials. Successes on the Western Front pushed the enemy back towards the German border, but the Royal Navy had constantly been squeezing Germany since 1914.

One only needs to look at the seabed to see the true cost of the war at sea. Around the shores of Britain and Ireland lie the remains of some 5,000 vessels sunk between 1914 and 1918. Along the south coast of England alone lie 1,100 ships. The vast majority are British merchant ships lost in this incredibly important strategic race between Germany and Britain.


[i] The internationally recognised border of the Antarctic Ocean has moved steadily south since the First World War. Although the chase between British and German ships that led to the Battles of Coronel and the Falklands occurred within the 1914 Antarctic Ocean, today they would be considered to have been in the South Atlantic.
[ii] Many other battles claim to be larger, but in terms of a battleship battle, and in terms of tonnage committed to direct action with one another, Jutland is clear winner over Philippine Sea (1944) and Leyte Gulf (1944).
[iii] It should be noted that attacks on merchant ships (theoretically in accordance with the rules of war) still occurred between these campaigns as and when patrolling submarines came across them. The campaigns represent periods of increased activity and greater numbers of U-boats at sea with a set mission to target merchant shipping.
[iv] Even today, 95% of Britain’s imports come by sea.
[v] Rear Admiral William Jameson (1965) The Most Formidable Thing. Rupert Hart-Davis, London.


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