Unrestricted submarine warfare is a type of naval warfare in which submarines sink merchant ships such as freighters and tankers without warning. The use of unrestricted submarine warfare has had significant impacts on international relations in regards to both the First World War and the Second World War. Its history has been dominated by German decision making.
There have been attempts to limit the use of unrestricted naval warfare, with some dating back to before the turn of the 20th Century as an extension of rules for surface raiders. While initially submarines operated successfully by attacking on the surface using deck guns, attacking without warning while submerged reduces the opportunity for the target to escape or defend itself if armed.
Customary naval law (specifically, so called cruiser rules) specified that while enemy warships may be attacked freely, civilian and neutral ships can only be interfered with if carrying contraband (announced previously in a contraband list), and the lives of the crew should be protected [1] . Formal limitations on warfare at sea date back to the 1899 Hague Convention. [2]
However, the Imperial German navy was heavily criticised internally by high level officials for their relative inactivity at the start of WWI. To boost the role of the navy, and buoyed by early successes of U-boat warfare, Admiral Tirpitz and Admiral von Pohl suggested a plan whereby U-boats, given a free hand to attack British (and in some cases, neutral) shipping, could potentially force Britain into a "concillatory mood" in as few as six weeks. The admirals appealed to public opinion through press interviews, [3] posing the submarines as "miracle weapons", despite the extremely small number of vessels available. It was believed that a "shock effect" would cause shipping to cease, and that neutrals would judge the campaign a reasonable reprisal for the British naval blockade. Chancellor Bethmann Hollweg accepted this strategy on February 1, 1915, and a directive issued the next day, with a public announcement on the 4th. [4]
In the most dramatic episode they sank Lusitania in May 1915 in a few minutes. [5] In the face of US anger, German Chancellor Bethmann Hollweg obtained a secret directive to exclude passenger vessels from being targeted and to make strenuous measures to avoid striking neutral vessels, a measure made into a formal and public suspension of unrestricted warfare after the sinking of Arabic in August 1915. Submarines operated under prize rules for 1916 - indeed even during 1915 the majority of attacks were made on the surface. [6]
Admiral Henning von Holtzendorff, chief of the Imperial Admiralty staff, argued successfully in early 1917 to resume the attacks and thus starve the British. The German high command realized the resumption of unrestricted submarine warfare meant war with the United States but calculated that American mobilization would be too slow to stop a German victory on the Western Front. [7] [8] The United States, who were previously neutral, joined the war in favour of the British. The decision made by Germany became one of the "trigger mechanisms" causing the US to enter the war. [9]
After World War I, there was a strong push to construct international rules prohibiting submarine attacks on merchant ships. [2] In 1922 the United States, the United Kingdom, Japan, France and Italy signed the Washington Treaty on Poison Gas and Submarines, to so restrict the use of submarines as to make them useless as commerce raiders. [10] France did not ratify, so the treaty did not go into effect.
In 1936, states signed the London Protocol on Submarine Warfare. To be deemed acceptable, naval attacks needed to follow prize rules, which called for warships to search merchantmen [11] and place crews in "a place of safety" [12] before sinking them.
Interwar prohibitions on unrestricted submarine warfare have been described as being too unspecified, thus leading to disagreements over how to interpret the rules and agreements. [2] For example, it was unclear what differentiated merchant ships from military ships, in particular given that Britain wanted to retain the rights to arm its merchants. [2] Furthermore, it was considered impractical for small submarines to take on the crews of noncombatant ships due to a lack of space. [2] Crews could be placed in emergency boats, but there was disagreement as to how safe that was. [2]
Prior to World War II, 48 states had accepted the prohibitions on unrestricted submarine warfare, including the great power combatants during World War II. [2] However states rapidly abandoned these restrictions: Mostly significantly Germany with War Order No. 154, and the US from the start of the War in the Pacific. [13]
There have been four major campaigns of unrestricted submarine warfare, one in World War I and three in World War II:
The four cases were attempts to impose a naval blockade on countries, especially those heavily dependent on merchant shipping to supply their war industries and feed their populations (such as Britain and Japan). Of these, the US submarine effort was by far the most successful, working together with mines to reduce the Japanese merchant fleet to less than a quarter its initial tonnage. [14]
U-boats were naval submarines operated by Germany, particularly in the First and Second World Wars. The term is an anglicised version of the German word U-Boot, a shortening of Unterseeboot, though the German term refers to any submarine. Austro-Hungarian Navy submarines were also known as U-boats.
The Battle of the Atlantic, the longest continuous military campaign in World War II, ran from 1939 to the defeat of Nazi Germany in 1945, covering a major part of the naval history of World War II. At its core was the Allied naval blockade of Germany, announced the day after the declaration of war, and Germany's subsequent counter-blockade. The campaign peaked from mid-1940 through to the end of 1943.
Carl Friedrich Heinrich Reinhard Scheer was an Admiral in the Imperial German Navy. Scheer joined the navy in 1879 as an officer cadet and progressed through the ranks, commanding cruisers and battleships, as well as senior staff positions on land. At the outbreak of World War I, Scheer was the commander of the II Battle Squadron of the High Seas Fleet. He then took command of the III Battle Squadron, which consisted of the newest and most powerful battleships in the navy. In January 1916, he was promoted to Admiral and given control of the High Seas Fleet. Scheer led the German fleet at the Battle of Jutland on 31 May – 1 June 1916, one of the largest naval battles in history.
Submarine warfare is one of the four divisions of underwater warfare, the others being anti-submarine warfare, mine warfare and mine countermeasures.
Commerce raiding is a form of naval warfare used to destroy or disrupt logistics of the enemy on the open sea by attacking its merchant shipping, rather than engaging its combatants or enforcing a blockade against them.
Henning Rudolf Adolf Karl von Holtzendorff was a German admiral during World War I, who became famous for his December 1916 memo about unrestricted submarine warfare against the United Kingdom. He was a recipient of Order of the Black Eagle and the Pour le Mérite with oak leaves and was one of just six Grand Admirals of the Imperial German Navy.
Hugo von Pohl was a German admiral who served during the First World War. He joined the Navy in 1872 and served in various capacities, including with the new torpedo boats in the 1880s, and in the Reichsmarineamt in the 1890s. He eventually reached the rank of Vizeadmiral and held the position of Chief of the Admiralty Staff in 1913. As Chief of the Admiralty Staff, Pohl was an outspoken advocate of unrestricted submarine warfare, and he put the policy into effect as he left the post on 1 February 1915.
Naval warfare in World War I was mainly characterised by blockade. The Allied Powers, with their larger fleets and surrounding position, largely succeeded in their blockade of Germany and the other Central Powers, whilst the efforts of the Central Powers to break that blockade, or to establish an effective counter blockade with submarines and commerce raiders, were eventually unsuccessful. Major fleet actions were extremely rare and proved less decisive.
SM U-20 was a German Type U 19 U-boat built for service in the Imperial German Navy. She was launched on 18 December 1912, and commissioned on 5 August 1913. During World War I, she took part in operations around the British Isles. U-20 became infamous following her sinking of the British ocean liner RMS Lusitania on 7 May 1915, an act that dramatically reshaped the course of World War I.
Defensively equipped merchant ship (DEMS) was an Admiralty Trade Division programme established in June 1939, to arm 5,500 British merchant ships with an adequate defence against enemy submarines and aircraft. The acronym DEMS was used to describe the ships carrying the guns, the guns aboard the ships, the military personnel manning the guns, and the shore establishment supporting the system.
Allied submarines were used extensively during the Pacific War and were a key contributor to the defeat of the Empire of Japan.
The Mediterranean U-boat Campaign in the Mediterranean Sea was fought by Austria-Hungary and German Empire against the Allies during World War I. It was characterised by the ability of the Central Powers to raid with near impunity during the first years of the war, causing substantial shipping losses, until the introduction of the convoy system allowed the Allies to drastically cut their losses from 1917 on.
SM UB-6 was a German Type UB I submarine or U-boat in the German Imperial Navy during World War I. The submarine was interned after running aground in neutral Dutch waters, and was scuttled by her crew at Hellevoetsluis.
The U-boat campaign from 1914 to 1918 was the World War I naval campaign fought by German U-boats against the trade routes of the Allies. It took place largely in the seas around the British Isles and in the Mediterranean. The German Empire relied on imports for food and domestic food production and the United Kingdom relied heavily on imports to feed its population, and both required raw materials to supply their war industry; the powers aimed, therefore, to blockade one another. The British had the Royal Navy which was superior in numbers and could operate on most of the world's oceans because of the British Empire, whereas the Imperial German Navy surface fleet was mainly restricted to the German Bight, and used commerce raiders and submarine warfare to operate elsewhere.
The Pless conference was a conference held at the castle of Prince Pless located in the Duchy of Pless on January 8, 1917. The conference involved the German army and navy arguing which division should take command of German activity in World War I. The German navy under Admiral Holtzendorff desired unrestricted submarine warfare to shut down the North Atlantic trade supplying Britain with food and munitions. The navy felt that it could starve Britain within six months to a year, before American troops could arrive on the Western Front and change the war. A memo was drafted by Admiral Holtzendorff in December 1916 before the Pless Conference, that argued for unrestricted submarine warfare. Pressure mounted on Kaiser Wilhem II to agree with the memo, which he had previously disagreed with due to his commitment to a policy of moderation.
The Atlantic U-boat campaign of World War I was the prolonged naval conflict between German submarines and the Allied navies in Atlantic waters—the seas around the British Isles, the North Sea and the coast of France.
The convoy—a group of merchantmen or troopships traveling together with a naval escort—was revived during World War I (1914–18), after having been discarded at the start of the Age of Steam. Although convoys were used by the Royal Navy in 1914 to escort troopships from the Dominions, and in 1915 by both it and the French Navy to cover their own troop movements for overseas service, they were not systematically employed by any belligerent navy until 1916. The Royal Navy was the major user and developer of the modern convoy system, and regular transoceanic convoying began in June 1917. They made heavy use of aircraft for escorts, especially in coastal waters, an obvious departure from the convoy practices of the Age of Sail.
The RMS Lusitania was a British-registered ocean liner that was torpedoed by an Imperial German Navy U-boat during the First World War on 7 May 1915, about 11 nautical miles off the Old Head of Kinsale, Ireland. The attack took place in the declared maritime war-zone around the UK, shortly after unrestricted submarine warfare against the ships of the United Kingdom had been announced by Germany following the Allied powers' implementation of a naval blockade against it and the other Central Powers. The passengers had been warned before departing New York of the danger of voyaging into the area in a British ship.
Cruiser rules, alternatively called prize rules is a colloquial phrase referring to the conventions regarding the attacking of a merchant ship by an armed vessel. Here cruiser is meant in its original meaning of a ship sent on an independent mission such as commerce raiding. A cruiser in modern naval terminology refers to a type of ship rather than its mission. Cruiser rules govern when it is permissible to open fire on an unarmed ship and the treatment of the crews of captured vessels, and are contrasted to unrestricted submarine warfare where submarines attack without warning and do not act to protect crew.
The 9 January 1917 Crown Council meeting, presided over by German Emperor Wilhelm II, decided on the resumption of unrestricted submarine warfare by the Imperial German Navy during the First World War. The policy had been proposed by the German military in 1916 but was opposed by the civilian government under Chancellor Theobald von Bethmann Hollweg who feared it would alienate neutral powers, including the United States.