The submarine war 1914–1918

Germany turned to unrestricted submarine warfare because it had no other way to strike at Britain. Its battle fleet could not break the British blockade, but submarines could sink the ships that brought food and raw materials to the British Isles. At the turn of 1916 and 1917 the Admiralty Staff and the Supreme Army Command convinced the Kaiser that sinking about 600,000 tons a month would force Britain to make peace before America could come to its aid. The calculation failed: the British introduced convoys, and the United States entered the war.

A new weapon at sea

At the start of the war the German navy had, depending on how they are counted, between 20 and 24 submarines, and it saw them as a weapon against warships. Their power was shown on 22 September 1914 by U-9 under Kapitänleutnant Otto Weddigen, which in little more than an hour sank three British armoured cruisers off the Dutch coast: the Aboukir, the Hogue and the Cressy. 1,459 sailors were killed. Only two weeks earlier U-21 had sunk the cruiser Pathfinder. Both sides realised that the submarine, until recently regarded as an auxiliary weapon, could threaten even large warships.

At the same time a war over trade was under way. From the first days of the war Britain published contraband lists, and on 2 November 1914 it declared the whole North Sea a military area, so as to stop ships bound for the Netherlands and Scandinavia more easily. The blockade did not close German ports directly, but it cut them off from overseas trade and deepened Germany’s shortages of food and raw materials. The Germans had no means of answering on the surface of the sea. They were left with submarines, which until then had attacked merchant ships rarely and usually under prize rules, like the commander of U-17, who before sinking the steamer Glitra ordered her crew into the boats.

The first campaign, 1915

On 4 February 1915 Germany declared the waters around Great Britain and Ireland a war zone, in which from 18 February every enemy merchant ship was to be destroyed. The proclamation was signed by Admiral Hugo von Pohl, the chief advocate of the campaign. Yet there was little strength behind the threatening words: Germany had just over twenty boats able to operate in British waters, and usually only a few could be there at the same time. In retaliation London tightened the blockade on 11 March: from then on no ship could sail to a German port.

The problem lay in the law of the sea. It required a warship to stop a merchant ship, search it and ensure the safety of the crew before sinking it. A small submarine, defenceless on the surface, could not do this without risk, especially once merchant ships were given guns. Once the zone came into force, U-boats therefore began to torpedo ships without warning, and sinking them together with their people provoked outrage in neutral countries, especially in the United States. President Woodrow Wilson warned that he would hold Germany to “strict accountability” for the deaths of American citizens.

On 7 May 1915 U-20 under Kapitänleutnant Walther Schwieger torpedoed the British liner Lusitania off the coast of Ireland. The ship sank within 18 minutes, and almost 1,200 people were killed, among them more than a hundred citizens of the United States. After the Lusitania a secret order banned attacks on large passenger ships without warning, but on 19 August U-24 torpedoed the liner Arabic, on which, according to most sources, 44 people died. This time Berlin understood that a break with Washington was at hand.

On 1 September 1915 Ambassador Johann Heinrich von Bernstorff assured Secretary of State Robert Lansing in writing that liners would not be sunk without warning and without ensuring the safety of non-combatants. The new Chief of the Admiralty Staff, Admiral Henning von Holtzendorff, in practice halted submarine operations around the British Isles on 18 September. The first campaign did not threaten Britain’s supplies, as it had the largest merchant fleet in the world, but it brought Germany its most serious crisis in relations with America.

The dispute in Berlin

For two years politicians and soldiers in Berlin argued over submarine warfare. The loudest advocate of using the U-boats ruthlessly was the State Secretary of the Navy, Grand Admiral Alfred von Tirpitz. Chancellor Theobald von Bethmann Hollweg feared that a blow against neutral shipping would push the United States against Germany. The decision was to rest with Kaiser Wilhelm II.

At the beginning of 1916 the dispute broke out again. A memorandum of the Admiralty Staff of 7 January promised that once all restrictions were lifted, Britain’s resistance would be broken within six months at the latest, and the Chief of the General Staff, Erich von Falkenhayn, backed it. The Chancellor won a compromise: from the end of February submarines could attack without warning only armed merchant ships. On 6 March the Kaiser postponed unrestricted submarine warfare indefinitely, and Tirpitz, who had not even been summoned to the conference, lost his post.

As early as 24 March UB-29 of the Flanders Flotilla torpedoed the ferry Sussex in the English Channel. At least 50 people were killed, and Americans were among the wounded. In its note of 18 April Washington threatened to break off diplomatic relations, and on 4 May Germany gave way: it pledged that submarines would not sink merchant ships without warning and without saving lives.

The commander of the High Seas Fleet, Admiral Reinhard Scheer, judged that in this form the war on trade was too dangerous for his boats, and withdrew them from it. After the Battle of Jutland he wrote to the Kaiser that even the most successful battle would not force Britain to make peace, and that only submarine warfare waged without restrictions could do so. In the autumn of 1916 the supporters of that war gained powerful allies. Paul von Hindenburg and Erich Ludendorff, the new heads of the army, no longer believed in victory on land after the bloody battles of Verdun and the Somme.

Unrestricted submarine warfare, 1917

On 22 December 1916 Holtzendorff sent Hindenburg a lengthy memorandum. In it he calculated that if submarines sank 600,000 tons a month without restriction, and at least two-fifths of neutral shipowners stopped sailing to England out of fear, then after five months British sea trade would shrink by 39 per cent. A unique opportunity was offered by the world’s poor grain harvest of 1916. Britain would therefore have to sue for peace before the harvest, that is before 1 August 1917. The risk of a break with America had to be accepted, “for no other choice remains to us”.

Bethmann Hollweg asked for a delay at least until the Entente had replied to the German peace offer, and Vice-Chancellor Karl Helfferich considered the Admiralty Staff’s figures pure speculation. On 9 January at Pless the Chancellor no longer put up a real fight. “Submarine warfare is the last card,” he said, but if the military authorities considered it necessary, he was not in a position to oppose them. The Kaiser ordered unrestricted submarine warfare to begin on 1 February.

On 31 January Bernstorff informed Washington that in zones around Great Britain, France and Italy and in the eastern Mediterranean every ship, neutral ones included, would be sunk without warning. According to the British official history of the war at sea, in February 1917 Germany had 111 submarines available for operations. From 1 February they began sinking ships without warning, and neutral shipowners, out of fear, kept their ships in port. In February alone ships totalling about 540,000 tons were sunk.

The United States responded quickly. On 3 February Wilson broke off diplomatic relations with Germany. To the dispatch carrying instructions on submarine warfare Berlin had attached a telegram from State Secretary Arthur Zimmermann proposing an alliance to Mexico. British intelligence intercepted it, and on 1 March its contents made the front pages of American newspapers.

When in March U-boats sank more American ships, Wilson asked Congress to recognise a state of war, and on 6 April 1917 the United States declared war on Germany. In his address to Congress Wilson called the German submarine warfare against commerce “a warfare against mankind” and said that “the world must be made safe for democracy”.

Convoys and the crisis of spring 1917

April 1917 was the worst month of the whole submarine war. The tallies give different figures because they count differently: some include only ships sunk by submarines, others also the victims of mines. The British official history of seaborne trade by C. Ernest Fayle gives 881,027 gross tons of ships of all flags lost through enemy action, including 545,282 tons of British shipping, and attributes about 847,000 tons to submarines and the rest to mines. According to other studies the U-boats alone sank from about 835,000 to more than 860,000 tons. Depending on the count, losses thus amounted to between about 835,000 and more than 880,000 tons.

The Admiralty under John Jellicoe long resisted convoys. It believed that a mass of ships would be an easy target, that masters would not keep station, and that there would not be enough escorts. Admiral William Sims, newly arrived in London, learned the true losses and asked for American destroyers to be sent. The first of them arrived at Queenstown on 4 May. On 26 April the head of the Anti-Submarine Division, Rear-Admiral Alexander Duff, recommended introducing convoys, and the next day Jellicoe agreed to a trial. On 30 April Prime Minister David Lloyd George came to the Admiralty. He later wrote that it was his visit that broke the admirals’ resistance, but naval historians point out that the decision on a trial had been taken earlier.

On 10 May the first trial convoy left Gibraltar, and on 20 May it reached Plymouth without loss. On 17 May the Admiralty set up a committee to draw up a permanent system. On 14 June Jellicoe approved the plan, and on 2 July the first convoy of the regular series sailed from Hampton Roads in Virginia. According to Fayle, from July to 27 October 1917 1,500 ships arrived safely in convoys from North America, Dakar, Sierra Leone and Gibraltar, while 24 were sunk.

Why did the U-boats lose? A submarine found it harder to locate a group of ships than single vessels, and when it attacked it exposed itself to a counter-attack by the escort. U-boats were also lost to mines, depth charges and fights with Q-ships. Above all, though, there were too few of them. According to the historian Holger Herwig, in 1917 on average only 32 boats were on patrol, while as early as 1914, before the war, Lieutenant Ulrich-Eberhard Blum of the Submarine Inspectorate at Kiel had calculated that an offensive against shipping around the British Isles would need at least 222.

The last year

At the beginning of 1918 Germany had more front-line boats in service than in April 1917, but convoys covered an ever larger share of shipping. According to Fayle, in the three months to the end of July 1918 losses averaged 271,000 tons a month, 60 per cent less than in the first three months of unrestricted submarine warfare. In the summer Allied shipyards and ship purchases at last began to keep pace with the losses.

The British tried to strike at the bases. The submarines of the Flanders Flotilla sailed from the port of Bruges through canals to Zeebrugge and Ostend. On 23 April 1918 the ships of Vice-Admiral Roger Keyes sank two old cruisers filled with concrete in the canal at Zeebrugge, while off Ostend the blockships ran aground. The raid caused enormous enthusiasm in the Entente countries, but as early as 25 April the first submarine again put to sea through Zeebrugge. A second attempt to block Ostend was made on the night of 9–10 May.

In August 1918 Scheer took charge of a new Naval War Command, and Eduard von Capelle left the Imperial Naval Office. The Scheer programme envisaged raising submarine production from fewer than 13 to 36 a month, but it no longer had any chance of being carried out. As the front approached the coast, the Germans withdrew their submarines from Flanders, and on 19 October the Belgians entered Bruges and Zeebrugge.

The U-boats’ last great blow was the sinking of the mail steamer Leinster on 10 October in the Irish Sea, in which about 560–570 people died. In his note of 14 October Wilson demanded that Germany cease its “illegal and inhumane practices”. Around 20–21 October Scheer recalled all submarines to their bases. The plan for a last battle of the fleet led to the Kiel mutiny.

Under the Armistice of Compiègne Germany had to hand over to the Allies every submarine fit to sail. On 20 November 1918 the first 20 U-boats surrendered off Harwich, and by April 1919 a total of 176 boats had been handed over there. Some were passed to France, Japan and other allies, and most were scrapped.

The balance

In 1914–1918 the German navy had, depending on the method of counting, between 351 and 375 submarines in service. It lost between 202 and 217 of them, 178 of them sunk by the enemy, and about 5,000 crewmen were killed. At the armistice 134 boats remained in service. The spread arises because some sources count only operational boats and others all those commissioned, and not all of them include among the losses the boats scuttled in the autumn of 1918.

The U-boats sank almost 5,000 ships with a combined tonnage of more than 12 million tons. The uboat.net database covers more than 7,600 attacks on more than 7,400 ships, including ships damaged and captured. Britain survived, but even after convoys were introduced, shipping losses for many months exceeded what could be built or acquired.

Historians’ debates

Was unrestricted submarine warfare Germany’s greatest mistake? Contemporaries already doubted the Admiralty Staff’s figures: Helfferich called them speculation, and Bethmann Hollweg spoke of the “last card”. Holtzendorff and the Supreme Army Command replied that Germany had no other choice. They reckoned with war with America, but believed its help would come too late. The Germans presented submarine warfare as a response to the British blockade, which deepened Germany’s food shortages.

The historian Holger Herwig of the University of Calgary points out that in quantitative terms the Admiralty Staff’s predictions proved very accurate, and yet Britain had not been “brought to its knees” by 1 August 1917. In his view the planners underestimated how much credit a modern industrial state can raise and how well it can adapt: the British rationed food, baked “war bread” mixed with other flours, ploughed up about a million acres of grassland and requisitioned neutral ships. According to Herwig, the rhetoric of this war was “total” but its reality was limited, above all by too small a number of boats. The entry of the United States into the war, in turn, turned the tide against Germany.