The use of unrestricted submarine warfare was announced by Germany on January 9th, 1917. The use of unrestricted submarine warfare was to have a major impact on World War One as it was one of the main reasons why America joined the war.

When the German Chancellor Bethmann Hollweg announced Germany’s intention to use unrestricted submarine warfare, his one major concern and fear was that it would provoke an American response – in this he was to be correct.

Why did Germany resort to such a tactic that was likely to provoke such a response from America? By 1917, the war was not going well for Germany on the Western Front. Unrestricted submarine warfare was a result of desperation and the belief that the ferocity of such a tactic might just keep America out of the war if the results were spectacular and shocking enough.

The Battle of Jutland showed that the German Navy was not strong enough to defeat the Royal Navy. Therefore any attempt by the German surface fleet to attack British merchant ships was not tenable as any fleet leaving bases like Kiel would have been met with a considerable fleet from the Royal Navy. Therefore, any attacks on Britain’s lifeline of shipping from America would have to be done by submarines. Rather than do this piecemeal, Bethmann Hollweg decided on a policy of wholesale unrestricted attack.

The impact of U-boats was overestimated in Germany. At the start of the war, the German submarine service had a couple of high profile successes against British naval targets but after this, successes became rare. However, the public in Germany had a high opinion as to the ability of the submarine to turn a campaign.

U-boats first attacked commercial targets as early as February 1915 but it was a piecemeal campaign. This ended in January 1917 when Bethmann Hollweg, persuaded by senior officers in the German Imperial Navy, ordered unrestricted attacks as part of policy. The one issue that had held Bethmann Hollweg back was the sinking of neutral ships. At that time America was a neutral state whose ships frequently and legally crossed the Atlantic with supplies for the Allies. Bethmann Hollweg’s views seem to have been based on a political perspective – the thought of angering America. The only person who was known to have expressed humanitarian views was the Kaiser who stated that the drowning of innocent civilians was “a dreadful thought”.

As early as 1915, Admiral von Pohl had wanted neutral shipping in the so-called ‘war zone’ (the English Channel and the rest of the water around the United Kingdom that then included the whole of the Irish coastline) attacked. He believed that the sinking of a few neutral merchant ships at the start of a campaign of unrestricted submarine warfare would be enough to scare off most ships from trading with Britain. However, on this occasion Pohl was not listened to for two reasons. The first was that the U-boat fleet was simply not big enough to execute a successful campaign against the numerous merchant ships that sailed around the British coast as in February 1915, there were only 21 U-boats available in total. At times only 4 U-boats patrolled the British coastline as some were in for repairs or an overhaul. Second, many still believed that such an approach was unethical and against the rules of war.

On February 18th, 1915, Germany announced that it would start a commerce war against those nations trading with Britain. Amongst others, America sent a strongly worded note to Berlin to state in very blunt terms that Germany would be held responsible for any American ship that was sunk. Germany’s military predicament in February 1915 was such that she could not afford to provoke a situation whereby America got involved in the war. Therefore, Bethmann-Hollweg persuaded senior naval officers to exclude neutral ships from the order – especially ships from America. On February 22nd, 1915, the U-boat commerce war started. In March 1915, 5,000 ships entered and left British ports. Only 21 were attacked. As a result of this, neutral shipping that had been put off by the declaration, soon resumed trading once again believing that they were all but safe from attack.

On May 7th, 1915, the British liner ‘Lusitania’ was sunk. Among the dead were 128 American citizens. The sinking caused outrage in America but not to the extent that President Woodrow Wilson was prepared to declare war on Germany. In fact, in a note written on July 23rd, 1915, Wilson wrote that Germany had changed her ways of attacking ships by submarine. The chosen method post-‘Lusitania’ was for a U-boat to come to the surface and use newly fitted deck guns to sink ships. Any neutral ship not carrying contraband was allowed to go to the port it was sailing for. Any neutral ship caught with contraband was sunk – but only after the crew had got off into lifeboats. This seemed sufficient for Wilson to remain pacified in 1915.

However, though the German government believed that this was the case, the German navy had no intention of carrying out such a policy claiming that the simple act of a submarine coming to the surface was too dangerous for their crews, especially as some merchant ships had been fitted with concealed guns. On June 6th, 1915, Wilhelm II ordered that all large passenger liners, whether neutral or not, must not be attacked. On August 19th, the ‘Arabic’, a British liner, was sunk without any form of warning being given. Two Americans died. The Kaiser then ordered that no passenger liner was to be attacked until all the crew and passengers had been given the chance to escape. In September 1915, Wilhelm changed his naval chief of staff. Vice-Admiral Bachmann was replaced by Admiral von Holtzendorff, a senior German naval officer who was supportive of Bethmann-Hollweg’s point of view. On September 18th, Holtzendorff ordered that all U-boats had to adopt the ‘cruiser’ system of warfare – coming to the surface before attacking a ship. The navy responded by ending all U-boat activity around the British Isles as they feared that the ‘cruiser’ style of attack was simply too dangerous for its submarines. In this sense, the loss of the ‘Arabic’ gave the British a respite from the threat of the U-boats.

On February 29th, 1916, Holtzendorff withdrew his order and what was termed “intensified” U-boat activity started. However, for the navy this was only a move towards what they wanted – unrestricted submarine warfare. By 1916, they also had a powerful supporter in the army – General Erich von Falkenhayn, chief of the army general staff. Falkenhayn was planning a major Western offensive targeting the huge French fort complex at Verdun. He, therefore, wanted any move possible that would weaken the Allies and improve his chances of success. This included unrestricted submarine warfare. Bethmann-Hollweg now faced the united front of the navy and army.

March 1916 was the key month as ‘intensified’ submarine activity was due to start in that month. On March 4th, Falkenhayn met Wilhelm II at Charleville. He put forward his arguments for unrestricted submarine warfare. Bethmann-Hollweg was also at the meeting and was allowed to do the same. He made two points – that there was still a danger of such a policy bring America into the war and second, Germany only had 14 large submarines that were capable of operating around the British coastline. Wilhelm could not make his mind up. He announced that he would announce his decision at the beginning of April. He never did. However on March 13th, the military and Bethmann-Hollweg did agree the following: that both armed and unarmed merchant ships in what was a designated war zone were to be destroyed without warning. Outside of the war zone, the old orders still applied. This decision was kept a secret. To the Americans, it seemed as if Germany had started unrestricted submarine warfare. On April 18th, the cross-Channel steamer ‘Sussex’ was torpedoed without warning. Two Americans were injured. Due to a breakdown in communications, Woodrow Wilson believed that Americans had been killed. He sent a note to the Germans threatening to break off diplomatic ties with Germany. This was interpreted by Bethmann-Hollweg as a very serious threat and, at the behest of his chancellor, Wilhelm II ordered that only the rules for ‘cruiser’ warfare were allowed and the March 13th order was dropped. In response, the U-boats stopped their campaign in British waters.

However, Falkenhayn kept up his efforts to persuade the Kaiser to allow unrestricted submarine warfare. He lost out to Bethmann-Hollweg. On May 4th, 1916, Germany agreed to the demands of the American government and informed Woodrow Wilson that Germany would adhere to international law. Germany also expressed its desire that America should pressure Britain to stop its ‘illegal’ blockade of Germany and if this was not forthcoming, Germany reserved the right to start up her submarine campaign. Wilson was pleased with the first part of the German response but not with the second. He told Germany that no American life should be threatened as a response of actions taken by the British government over which the Americans had no control.

However, by mid-1916, the military situation was working against Bethmann-Hollweg. The appalling loss of life at Verdun and the Somme had led to Falkenhayn being replaced by Hindenburg and Luderndorff (August 27th, 1916). Bethmann-Hollweg had always fought for Hindenburg to be Germany’s chief of the army’s general staff as he believed that both he and Hindenburg shared similar beliefs. However, in this he was to be wrong. Hindenburg was a supporter of unrestricted submarine warfare. As 1916 moved into 1917, the impact of Britain’s blockade of Germany was having a major effect. To both Hindenburg and Luderndorff, Germany was threatened with exhaustion. The military situation Germany found herself in at the end of 1916, was not favourable as the loss of life at the Somme and Verdun had been huge. Both Hindenburg and Luderndorff believed that unrestricted submarine warfare was the only solution to Germany’s mounting problems.

By 1917, Germany was in a better position to engage in unrestricted submarine warfare. She had a fleet of 46 large submarines capable of operating in deep water. Germany also had 23 U-boats that could operate at a coastal level. German naval intelligence believed that unrestricted submarine warfare would result in the loss of 600,000 tons of shipping per month – double the tonnage that ‘cruiser’ warfare accounted for. Coupled with the internationally bad harvest of 1916, there was a belief in Berlin that Britain could be starved into defeat within 5 months. The military believed that America would not enter the war while politicians were less sure. However, Bethmann-Hollweg’s stance was hindered by the fact that the Reichstag’s main parties supported unrestricted submarine warfare. In his memoirs Bethmann-Hollweg wrote:

“No nation will stand for not winning a war when it is convinced that it can win.”

On January 9th, 1917, Bethmann-Hollweg went to a meeting at Pless. He found the navy’s and army’s hierarchy against him – and they had already won over the Kaiser. The decision for unrestricted submarine warfare was made on that day and it started on February 1st 1917.

Wilson broke off diplomatic relations with Germany in an effort to bring Germany to its senses. He hoped that such an action would force Germany to go back on its decision. This did not happen and relations between America and Germany became very strained when British intelligence intercepted a message from Germany to Mexico whereby Germany offered her support to Mexico if America entered the war against Germany because of unrestricted submarine warfare. By March 21st, seven American merchant ships had been sunk by the Germans. Wilson summoned Congress and on April 6th 1917, America entered the war.