U-boat Campaign (World War I)
Overview
 
The U-boat Campaign from 1914 to 1918 was the World War I
World War I
World War I , which was predominantly called the World War or the Great War from its occurrence until 1939, and the First World War or World War I thereafter, was a major war centred in Europe that began on 28 July 1914 and lasted until 11 November 1918...

 naval
Naval warfare
Naval warfare is combat in and on seas, oceans, or any other major bodies of water such as large lakes and wide rivers.-History:Mankind has fought battles on the sea for more than 3,000 years. Land warfare would seem, initially, to be irrelevant and entirely removed from warfare on the open ocean,...

 campaign fought by German U-boat
U-boat
U-boat is the anglicized version of the German word U-Boot , itself an abbreviation of Unterseeboot , and refers to military submarines operated by Germany, particularly in World War I and World War II...

s against the trade routes of the Entente Powers. It took place largely in the seas around the British Isles
British Isles
The British Isles are a group of islands off the northwest coast of continental Europe that include the islands of Great Britain and Ireland and over six thousand smaller isles. There are two sovereign states located on the islands: the United Kingdom of Great Britain and Northern Ireland and...

 and in the Mediterranean.

The German Empire
German Empire
The German Empire refers to Germany during the "Second Reich" period from the unification of Germany and proclamation of Wilhelm I as German Emperor on 18 January 1871, to 1918, when it became a federal republic after defeat in World War I and the abdication of the Emperor, Wilhelm II.The German...

 relied on imports for food and domestic food production (especially fertilizer) and the United Kingdom
United Kingdom of Great Britain and Ireland
The United Kingdom of Great Britain and Ireland was the formal name of the United Kingdom during the period when what is now the Republic of Ireland formed a part of it....

 relied heavily on imports to feed its population, and both required raw materials to supply their war industry; the powers aimed, therefore, to blockade
Blockade
A blockade is an effort to cut off food, supplies, war material or communications from a particular area by force, either in part or totally. A blockade should not be confused with an embargo or sanctions, which are legal barriers to trade, and is distinct from a siege in that a blockade is usually...

 one another.
Encyclopedia
The U-boat Campaign from 1914 to 1918 was the World War I
World War I
World War I , which was predominantly called the World War or the Great War from its occurrence until 1939, and the First World War or World War I thereafter, was a major war centred in Europe that began on 28 July 1914 and lasted until 11 November 1918...

 naval
Naval warfare
Naval warfare is combat in and on seas, oceans, or any other major bodies of water such as large lakes and wide rivers.-History:Mankind has fought battles on the sea for more than 3,000 years. Land warfare would seem, initially, to be irrelevant and entirely removed from warfare on the open ocean,...

 campaign fought by German U-boat
U-boat
U-boat is the anglicized version of the German word U-Boot , itself an abbreviation of Unterseeboot , and refers to military submarines operated by Germany, particularly in World War I and World War II...

s against the trade routes of the Entente Powers. It took place largely in the seas around the British Isles
British Isles
The British Isles are a group of islands off the northwest coast of continental Europe that include the islands of Great Britain and Ireland and over six thousand smaller isles. There are two sovereign states located on the islands: the United Kingdom of Great Britain and Northern Ireland and...

 and in the Mediterranean.

The German Empire
German Empire
The German Empire refers to Germany during the "Second Reich" period from the unification of Germany and proclamation of Wilhelm I as German Emperor on 18 January 1871, to 1918, when it became a federal republic after defeat in World War I and the abdication of the Emperor, Wilhelm II.The German...

 relied on imports for food and domestic food production (especially fertilizer) and the United Kingdom
United Kingdom of Great Britain and Ireland
The United Kingdom of Great Britain and Ireland was the formal name of the United Kingdom during the period when what is now the Republic of Ireland formed a part of it....

 relied heavily on imports to feed its population, and both required raw materials to supply their war industry; the powers aimed, therefore, to blockade
Blockade
A blockade is an effort to cut off food, supplies, war material or communications from a particular area by force, either in part or totally. A blockade should not be confused with an embargo or sanctions, which are legal barriers to trade, and is distinct from a siege in that a blockade is usually...

 one another. The British had the Royal Navy
Royal Navy
The Royal Navy is the naval warfare service branch of the British Armed Forces. Founded in the 16th century, it is the oldest service branch and is known as the Senior Service...

 which was superior in numbers and could operate on most of the world's oceans because of the British Empire
British Empire
The British Empire comprised the dominions, colonies, protectorates, mandates and other territories ruled or administered by the United Kingdom. It originated with the overseas colonies and trading posts established by England in the late 16th and early 17th centuries. At its height, it was the...

, whereas the German Kaiserliche Marine
Kaiserliche Marine
The Imperial German Navy was the German Navy created at the time of the formation of the German Empire. It existed between 1871 and 1919, growing out of the small Prussian Navy and Norddeutsche Bundesmarine, which primarily had the mission of coastal defense. Kaiser Wilhelm II greatly expanded...

 surface fleet was mainly restricted to the German Bight
German Bight
German Bight is the southeastern bight of the North Sea bounded by the Netherlands and Germany to the south, and Denmark and Germany to the east . To the north and west it is limited by the Dogger Bank. The Bight contains the Frisian and Danish Islands. The Wadden Sea is approximately ten to...

, and used commerce raiders and unrestricted submarine warfare
Unrestricted submarine warfare
Unrestricted submarine warfare is a type of naval warfare in which submarines sink merchantmen without warning, as opposed to attacks per prize rules...

 to operate elsewhere.

The successful blockade of Germany
Blockade of Germany
The Blockade of Germany, or the Blockade of Europe, occurred from 1914-1919 and was a prolonged naval operation conducted by the Allied Powers during and after World War I in an effort to restrict the maritime supply of raw materials and foodstuffs to the Central Powers, which included Germany,...

 contributed to its military defeat in 1918, and, still in effect, enforced the signing of the Treaty of Versailles
Treaty of Versailles
The Treaty of Versailles was one of the peace treaties at the end of World War I. It ended the state of war between Germany and the Allied Powers. It was signed on 28 June 1919, exactly five years after the assassination of Archduke Franz Ferdinand. The other Central Powers on the German side of...

 in mid-1919.

North Sea: Initial stage

In August 1914, a flotilla of ten U-boats sailed from their base in Heligoland
Heligoland
Heligoland is a small German archipelago in the North Sea.Formerly Danish and British possessions, the islands are located in the Heligoland Bight in the south-eastern corner of the North Sea...

 to attack Royal Navy
Royal Navy
The Royal Navy is the naval warfare service branch of the British Armed Forces. Founded in the 16th century, it is the oldest service branch and is known as the Senior Service...

 warships in the North Sea
North Sea
In the southwest, beyond the Straits of Dover, the North Sea becomes the English Channel connecting to the Atlantic Ocean. In the east, it connects to the Baltic Sea via the Skagerrak and Kattegat, narrow straits that separate Denmark from Norway and Sweden respectively...

 in the first submarine war patrol in history. Their aim was to sink capital ships of the British Grand Fleet, and so reduce the Grand Fleet's numerical superiority over the German High Seas Fleet. The first sortie was not a success. Only one attack was carried out, when U-15 fired a torpedo (which missed) at HMS Monarch
HMS Monarch (1911)
HMS Monarch was an Orion-class battleship of the Royal Navy. She served in the 2nd Battle Squadron of the Grand Fleet in World War I, and fought at the Battle of Jutland, 31 May 1916, suffering no damage....

. Two of the ten U-boats were lost.

Later in the month, the U-boats achieved success, when U-21 sank the cruiser HMS Pathfinder. In September, U-9 sank three armored cruisers (Aboukir, Hogue, and Cressy) in a single action. Other successes followed. In October U-9 sank the cruiser Hawke, and on the last day of the year U-24 sank the "pre-dreadnought
Pre-dreadnought
Pre-dreadnought battleship is the general term for all of the types of sea-going battleships built between the mid-1890s and 1905. Pre-dreadnoughts replaced the ironclad warships of the 1870s and 1880s...

" battleship HMS Formidable
HMS Formidable (1898)
HMS Formidable —the third of four ships of that name to serve in the Royal Navy—was the lead ship of her class of pre-dreadnought battleships. She was the second British battleship to be sunk by enemy action during the First World War...

. By the end of the initial campaign the U-boats had sunk nine warships while losing five of their own number.

Mediterranean: Initial stage

The initial phase of the U-boat campaign in the Mediterranean comprised the actions by the Austro-Hungarian Navy
Austro-Hungarian Navy
The Austro-Hungarian Navy was the naval force of Austria-Hungary. Its official name in German was Kaiserliche und Königliche Kriegsmarine , abbreviated as k.u.k. Kriegsmarine....

 (KuK)'s U-boat force against the French, who were blockading the Straits of Otranto.
At the start of hostilities the KuK had seven U-boats in commission; 5 operational, 2 training; all were of the coastal type, with limited range and endurance, suitable for operation in the Adriatic.
Nevertheless they had a number of successes. On
21 December 1914 U-12
SM U-12 (Austria-Hungary)
SM U-12 or U-XII was a U-5-class submarine or U-boat built for and operated by the Austro-Hungarian Navy before and during the First World War.- Introduction :Built on speculation by Whitehead & Co...

 torpedoed dreadnought Jean Bart
French battleship Jean Bart (1911)
Jean Bart was the second ship of the s, the first dreadnoughts built for the French Navy. She was completed before World War I as part of the 1910 naval building programme. She spent the war in the Mediterranean and helped to sink the Austro-Hungarian protected cruiser on 16 August 1914...

, causing her to retire, and on 27 April 1915 U-5
SM U-5 (Austria-Hungary)
SM U-5 or U-V was the lead boat of the U-5 class of submarines or U-boats built for and operated by the Austro-Hungarian Navy before and during the First World War. The submarine was built as part of a plan to evaluate foreign submarine designs, and was the first of three boats of the class built...

 sank cruiser Leon Gambetta
French armoured cruiser Léon Gambetta
The Léon Gambetta was a French Navy armoured cruiser of 12,400 tons, the lead ship of the her class. The Gambettas were larger than previous armoured cruisers of the class, but they lacked the heavier firepower. They also were vulnerable to underwater attacks.-Early history:She was launched on 26...

, with a heavy loss of life.
But the KuK boats were unable to offer any interference to allied traffic in the Mediterranean beyond the Straits of Otranto.

Submarine warfare

In 1914 the U-boat's chief advantage was to submerge; surface ships had no means to detect a submarine underwater, and no means to attack even if they could, while in the torpedo
Torpedo
The modern torpedo is a self-propelled missile weapon with an explosive warhead, launched above or below the water surface, propelled underwater towards a target, and designed to detonate either on contact with it or in proximity to it.The term torpedo was originally employed for...

 the U-boat had a weapon that could sink an armoured warship with one shot.
Its disadvantages were less obvious, but became apparent during the campaign. While submerged the U-boat was virtually blind and immobile; boats of this era had limited underwater speed and endurance, so needed to be in position before an attack took place, while even on the surface their speed (around 15 knots) was less than the cruising speed of most warships and two thirds that of the most modern dreadnoughts.

The U-boats scored a number of impressive successes, and were able to
drive the Grand Fleet from its base in search of a safe anchorage, but the German Navy was unable to erode the Grand Fleet's advantage as hoped.
Also, in the two main surface actions of this period the U-boat was unable to have any effect; the High Seas Fleet
High Seas Fleet
The High Seas Fleet was the battle fleet of the German Empire and saw action during World War I. The formation was created in February 1907, when the Home Fleet was renamed as the High Seas Fleet. Admiral Alfred von Tirpitz was the architect of the fleet; he envisioned a force powerful enough to...

 was unable to draw the Grand Fleet into a U-boat trap.
Whilst warships were travelling at speed and on an erratic zigzag
Zigzag
A zigzag is a pattern made up of small corners at variable angles, though constant within the zigzag, tracing a path between two parallel lines; it can be described as both jagged and fairly regular....

 course they were relatively safe, and for the remainder of the war
the U-boats were unable to mount a successful attack on a warship travelling in this manner.

First attacks on merchant ships

The first attacks on merchant ships had started in October 1914.
At that time there was no plan for a concerted U-boat offensive against Allied trade. It was recognized the U-boat had several drawbacks as a commerce raider, and such a campaign risked alienating neutral opinion.
In the six months to the opening of the commerce war in February 1915, U-boats had sunk 19 ships, totalling 43000 GRT.

Unrestricted submarine warfare

By early 1915, all the combatants had lost the illusion that the war could be won quickly, and began to consider harsher measures in order to gain an advantage.

The British, with their overwhelming sea power, had established a naval blockade of Germany immediately on the outbreak of war in August 1914, and in early November 1914 declared it to be a War Zone, with any ships entering the North Sea doing so at their own risk. The blockade was unusually restrictive in that even foodstuffs were considered "contraband of war". The Germans regarded this as a blatant attempt to starve the German people into submission and wanted to retaliate in kind, and in fact the severity of the British blockade did not go over well in America, either.

Germany could not possibly deal with British naval strength on an even basis, and the only possible way Germany could impose a blockade on Britain was through the U-boat. The German Chancellor, Theobald von Bethmann Hollweg, felt that such a submarine blockade, based on "shoot without warning", would antagonise the United States and other neutrals. However, he was unable to hold back the pressures for taking such a step.

In response to the British declaration in November 1914 that the entire North Sea was now a War Zone, on 4 February 1915 Admiral Hugo von Pohl
Hugo von Pohl
Hugo von Pohl was a German admiral who during the First World War commanded the German High Seas Fleet from 1915 until shortly before his death from illness in 1916....

, commander of the German High Seas Fleet, published a warning in the Deutscher Reichsanzeiger (Imperial German Gazette):

In time, this would bring non-European nations (such as Brazil and the United States) into the war.

The German U-boat force was now primarily based at Ostend
Ostend
Ostend  is a Belgian city and municipality located in the Flemish province of West Flanders. It comprises the boroughs of Mariakerke , Stene and Zandvoorde, and the city of Ostend proper – the largest on the Belgian coast....

 in Belgium, giving the submarines better access to the sea lanes around England. The Germans made use of this advantage, sending out about 20 U-boats to begin the naval blockade. In January, before the declaration of "unrestricted submarine warfare" as the submarine blockade was called, 43,550 tonnes of shipping had been sunk by U-boats. The number of sinkings then steadily increased, with 168,200 tonnes going down in August. Attacking without warning, German U-Boats sank nearly 100,000 GRT
Gross Register Tonnage
Gross register tonnage a ship's total internal volume expressed in "register tons", one of which equals to a volume of . It is calculated from the total permanently enclosed capacity of the vessel. The ship's net register tonnage is obtained by reducing the volume of non-revenue-earning spaces i.e...

 per month, an average of 1.9 ships daily.

On 10 April 1915 the British steamer Harpalyce, a Belgian relief ship and clearly marked as such, was torpedoed without warning by UB-4 near the North Hinder lightship, just outside the strip of sea declared safe by von Pohl. The ship had been en route for America to collect food for starving Belgians, and its sinking outraged American citizens already unhappy at the death of Leon C. Thrasher, drowned when the SS Falaba was sunk on 28 March 1915 by U-28 (Thrasher incident
Thrasher Incident
The Thrasher incident, as it became known in U.S. media, nearly became the start of America's involvement in World War I. On March 28, 1915, the British steamship was torpedoed and sunk by German U-boat...

).

RMS Lusitania

On 7 May 1915, the liner RMS Lusitania
RMS Lusitania
RMS Lusitania was a British ocean liner designed by Leonard Peskett and built by John Brown and Company of Clydebank, Scotland. The ship entered passenger service with the Cunard Line on 26 August 1907 and continued on the line's heavily-traveled passenger service between Liverpool, England and New...

 was torpedoed by U-20, 13 mi (20.9 km) off the Old Head of Kinsale
Old Head of Kinsale
The Old Head of Kinsale, is a headland near Kinsale, County Cork, Ireland. An early lighthouse was established here in the 17th century by Robert Reading...

, Ireland, and sank in just 18 minutes. Of the 1,959 people aboard, 1,198 were killed, 128 of them US citizens.

Following the incident, the German government attempted to justify it with a range of arguments, which are still debated today; nevertheless there was massive outrage in Britain and America, and the British felt that the Americans had to declare war on Germany. However, US President Woodrow Wilson
Woodrow Wilson
Thomas Woodrow Wilson was the 28th President of the United States, from 1913 to 1921. A leader of the Progressive Movement, he served as President of Princeton University from 1902 to 1910, and then as the Governor of New Jersey from 1911 to 1913...

 refused to over-react, though the massive loss of life caused by the sinking of Lusitania required a definitive response from the US.

When Germany began its submarine campaign against Britain, Wilson had warned that the US would hold the German government strictly accountable for any violations of American rights.
Backed by State Department second-in-command Robert Lansing
Robert Lansing
Robert Lansing served in the position of Legal Advisor to the State Department at the outbreak of World War I where he vigorously advocated against Britain's policy of blockade and in favor of the principles of freedom of the seas and the rights of neutral nations...

, Wilson made his position clear in three notes to the German government issued on 13 May, 9 June, and 21 July.

The first note affirmed the right of Americans to travel as passengers on merchant ships and called for the Germans to abandon submarine warfare against commercial vessels, whatever flag they sailed under.

In the second note Wilson rejected the German arguments that the British blockade was illegal, and was a cruel and deadly attack on innocent civilians, and their charge that the Lusitania had been carrying munitions. William Jennings Bryan considered Wilson's second note too provocative and resigned in protest after failing to have it moderated.

The third note, of 21 July, issued an ultimatum, to the effect that the US would regard any subsequent sinkings as "deliberately unfriendly". While the American public and leadership were not ready for war, the path to an eventual declaration of war had been set as a result of the sinking of the Lusitania.

Submarine minelayers

The appearance of new minefields off the East coast of Britain in June 1915 was puzzling to the Royal Navy due to the waters being very busy, and was blamed initially on neutral fishing boats. However, on 2 July the small coaster Cottingham accidentally ran down the small coastal U-boat UC-2
SM UC-2
SM UC-2 was a German Type UC I minelayer submarine or U-boat in the German Imperial Navy during World War I. The U-boat had been ordered by November 1914 and was launched on 12 May 1915...

 off Great Yarmouth
Great Yarmouth
Great Yarmouth, often known to locals as Yarmouth, is a coastal town in Norfolk, England. It is at the mouth of the River Yare, east of Norwich.It has been a seaside resort since 1760, and is the gateway from the Norfolk Broads to the sea...

, and when she was salvaged she was found to be a submarine minelayer, fitted with twelve mines in six launching chutes.

On August 21 UC-5 became the first submarine minelayer to penetrate into the English Channel, laying 12 mines off Boulogne, one of which sank the steamship William Dawson the same day. UC-5 laid 6 more mines off Boulogne and Folkestone
Folkestone
Folkestone is the principal town in the Shepway District of Kent, England. Its original site was in a valley in the sea cliffs and it developed through fishing and its closeness to the Continent as a landing place and trading port. The coming of the railways, the building of a ferry port, and its...

 on 7 September, one of which sank the cable layer Monarch. Further mines were laid off the southeast coast by UC-1
SM UC-1
SM UC-1 was a German Type UC I minelayer submarine or U-boat in the German Imperial Navy during World War I. The U-boat had been ordered by November 1914 and was launched on 26 April 1915...

, UC-3
SM UC-3
SM UC-3 was a German Type UC I minelayer submarine or U-boat in the German Imperial Navy during World War I. The U-boat had been ordered by November 1914 and was launched on 28 May 1915...

, UC-6
SM UC-6
SM UC-6 was a German Type UC I minelayer submarine or U-boat in the German Imperial Navy during World War I. The U-boat had been ordered by November 1914 and was launched on 20 June 1915...

, and UC-7
SM UC-7
SM UC-7 was a German Type UC I minelayer submarine or U-boat in the German Imperial Navy during World War I. The U-boat had been ordered by November 1914 and was launched on 6 July 1915...

.

SS Arabic

On 19 August 1915 U-24
SM U-24
SM U-24 was one of 329 submarines serving in the Imperial German Navy in World War I. She was engaged in commerce warfare during the First Battle of the Atlantic....

 sank the White Star
White Star Line
The Oceanic Steam Navigation Company or White Star Line of Boston Packets, more commonly known as the White Star Line, was a prominent British shipping company, today most famous for its ill-fated vessel, the RMS Titanic, and the World War I loss of Titanics sister ship Britannic...

 liner , outward bound for America, 50 mi (80.5 km) south of Kinsale
Kinsale
Kinsale is a town in County Cork, Ireland. Located some 25 km south of Cork City on the coast near the Old Head of Kinsale, it sits at the mouth of the River Bandon and has a population of 2,257 which increases substantially during the summer months when the tourist season is at its peak and...

. He fired a single torpedo which struck the liner aft, and she sank within 10 minutes, with the loss of 44 passengers and crew, 3 of whom were American. Following speculation that the US would sever relations with Germany,
on 28 August the Chancellor issued new orders to submarine commanders and relayed them to Washington. The new orders stated that until further notice, all passenger ships could only be sunk after warning and the saving of passengers and crews.
This proved unacceptable to the Naval High Command, and on 18 September the High Seas flotillas were withdrawn from the commerce war.

Dardanelles operations

The German Navy sent their first submarines to the Mediterranean in response to the Anglo-French Dardanelles campaign, after it became obvious that their Austro-Hungarian allies could do little against it with their small submarine force, which nevertheless was successful in defending the Adriatic.
The first U-boats sent, U-21
SM U-21 (Germany)
SM U-21 was one of the most famous U-boats to serve in the Imperial German Navy in World War I. She was the first submarine to sink a ship with a self-propelled torpedo. She also sank the British battleships HMS Triumph and HMS Majestic...

 and the two small coastal boats, UB-7 and UB-8, achieved initial success, U-21 sinking the Royal Navy predreadnought battleships HMS Triumph
HMS Triumph (1903)
HMS Triumph was a Swiftsure class pre-dreadnought battleship of the Royal Navy.-Technical characteristics:HMS Triumph was ordered by Chile as Libertad, laid down by Vickers at Barrow-in-Furness on 26 February 1902, and launched on 12 January 1903...

 and HMS Majestic
HMS Majestic (1895)
HMS Majestic was a Majestic-class predreadnought battleship of the Royal Navy.-Technical characteristics:HMS Majestic was laid down at Portsmouth Dockyard on 5 February 1894 and launched on 31 January 1895...

 on 25 and 27 May respectively on her way to Constantinople, but ran into severe limitations in the Dardanelles, where swarms of small craft and extensive anti-submarine netting and booms restricted their movements.

By the end of June 1915, the Germans had assembled a further 3 prefabricated Type UB I
German type UB I submarine
The Type UB I was a class of small coastal submarines built in Germany at the beginning of the First World War. Twenty boats were constructed, most of which went into service with the German Imperial Navy. Boats of this design were also operated by the Austro-Hungarian Navy and the Bulgarian...

 submarines at Pola, 2 of which were to be transferred to the Austrian Navy. They were also assembling 3 Type UC I
German Type UC I submarine
The Type UC I submarines were a class of small coastal minelaying U-boats built in Germany during the early part of World War I. They were the first operational minelaying submarines in the world . A total of fifteen boats were built...

 minelaying submarines, which were ordered converted into transports to carry small quantities of critical supplies to Turkey.

Mediterranean operations

The Mediterranean was an attractive theater of operations to the German Admiralstab
Seekriegsleitung
The Seekriegsleitung or SKL was the high command of the Kaiserliche Marine and the Kriegsmarine of Germany during the World Wars.It led planning and execution of naval combat and directed the distribution of naval forces...

; a significant proportion of British imports passed through it, it was critical to French and Italian trade, and submarines would be able to operate effectively in it even in autumn and winter when poor weather hampered Atlantic and North Sea operations. Additionally, there were certain choke points through which shipping had to pass, such as the Suez Canal
Suez Canal
The Suez Canal , also known by the nickname "The Highway to India", is an artificial sea-level waterway in Egypt, connecting the Mediterranean Sea and the Red Sea. Opened in November 1869 after 10 years of construction work, it allows water transportation between Europe and Asia without navigation...

, Malta
Malta
Malta , officially known as the Republic of Malta , is a Southern European country consisting of an archipelago situated in the centre of the Mediterranean, south of Sicily, east of Tunisia and north of Libya, with Gibraltar to the west and Alexandria to the east.Malta covers just over in...

, Crete
Crete
Crete is the largest and most populous of the Greek islands, the fifth largest island in the Mediterranean Sea, and one of the thirteen administrative regions of Greece. It forms a significant part of the economy and cultural heritage of Greece while retaining its own local cultural traits...

, and Gibraltar
Gibraltar
Gibraltar is a British overseas territory located on the southern end of the Iberian Peninsula at the entrance of the Mediterranean. A peninsula with an area of , it has a northern border with Andalusia, Spain. The Rock of Gibraltar is the major landmark of the region...

. Finally, the Mediterranean offered the advantage that fewer neutral ships would be encountered, such as US or Brazilian vessels, since fewer non European citizens then travelled the waters.

Throughout the summer, the Germans assembled a force of 4 boats at Cattaro for operations against commerce in the Mediterranean. The campaign got underway in October 1915, when U-33 and U-39, followed later by U-35, were ordered to attack the approaches to Salonika and Kavalla. That month, 18 ships were sunk, for a total of 63,848 tons. It was decided the same month that further reinforcements were called for, and a further large U-boat, U-38 sailed for Cattaro. Since Germany was not yet at war with Italy, even though Austria was, the German submarines were ordered to refrain from attacking Italian shipping in the eastern Mediterranean where the Italians might expect hostile action only from German submarines. When operating in the west, up to the line of Cape Matapan
Cape Matapan
Cape Tainaron , also known as Cape Matapan , is situated at the end of the Mani, Laconia, Greece. Cape Matapan is the southernmost point of mainland Greece. It separates the Messenian Gulf in the west from the Laconian Gulf in the east.-History:...

, the German U-boats flew the Austrian flag, and a sinking without warning policy was adopted, since large merchant ships could be attacked on the suspicion of being transports or auxiliary cruisers.

The German Admiralty also decided that the Type UB II
German type UB II submarine
The UB II type submarine was a class of U-boat built during World War I by the Kaiserliche Marine. They were enlarged from the preceding type UB I and were more effective vessels. The boats were a single hull design with a 50 metre maximum diving depth and a 30-45 second diving time...

 submarine would be ideal for Mediterranean service. Since these were too large to be shipped in sections by rail to Pola like the Type UB I, the materials for their construction and German workers to assemble them were sent instead. This meant a shortage of workers to complete U-boats for service in home waters, but it seemed justified by the successes in the Mediterranean in November, when 44 ships were sunk, for a total of 155,882 tons. The total in December fell to 17 ships (73,741 tons) which was still over half the total tonnage sunk in all theaters of operation at the time.

In November 1915 U-38 caused a diplomatic incident when she sank the Italian steamer Ancona
SS Ancona
SS Ancona was an Italian passenger steamer, built in 1908 by Workman, Clark & Co., Ltd., Belfast, and operated by the Society di Navigazione a Vaporetti Italia, of Genoa....

 while sailing under the Austrian flag, and the loss of 40 American citizens caused the "sinking without warning" policy to be abandoned until the resumption of unrestricted submarine warfare in 1917. A similar "false flag" incident in March 1916 was an influence on Italy's decision to declare war on Germany in August 1916.

Allied countermeasures

Allied countermeasures during this period had mixed success.

Defensive measures, such as arming merchant ships, and advising them to either run, or turn towards the U-boat in order to ram, or force it to submerge, were the most effective.,
From arming ships for self defence, the next step was arming ships for the purpose of engaging the U-boats in gun battles; 2 U-boats were sunk in 1915 whilst attacking trawlers so fitted. The following step was to arm and man ships with hidden guns to do so, the so-called Q ship. A variant on the idea was to equip small vessels with a submarine escort. In 1915 2 U-boats were sunk by Q-ships, and 2 more by submarines accompanying trawlers.

Offensive measures were less effective; efforts were made to use nets to find submerged U-boats, and explosive sweeps to destroy them, but these were largely failures.
Attempts were also made to close routes like the Straits of Dover with boom nets and minefields, the so-called Dover Barrage; to lay minefields around U-boat bases, and station submarines on patrol to catch them leaving or entering port. These measures required a huge expenditure of effort and material, but met with little success. Just 2 U-boats were sunk by these measures in 1915.

At the beginning of this period the British Merchant Marine had a shipping fleet totaling of 21 million GRT
Tonnage
Tonnage is a measure of the size or cargo carrying capacity of a ship. The term derives from the taxation paid on tuns or casks of wine, and was later used in reference to the weight of a ship's cargo; however, in modern maritime usage, "tonnage" specifically refers to a calculation of the volume...

.
In six months of unrestricted submarine warfare U-boats sank ¾ million tons of Allied shipping, scarcely denting the British merchant fleet; Whilst new building, and additions from ships seized, had more than made up this loss.
On the other hand, serious offence had been given to neutrals such as Norway and the Netherlands, and brought the United States to the brink of war. This failure, and the various restrictions imposed on the U-boat Arm in the Atlantic area largely brought the campaign there to a halt, although it continued with little hindrance in the Mediterranean and elsewhere, where there was less likelihood of offending neutrals.

Depth charges

The depth charge, or "dropping mine" as it was initially named, was first mooted in 1910, and developed into practicality when the British Royal Navy
Royal Navy
The Royal Navy is the naval warfare service branch of the British Armed Forces. Founded in the 16th century, it is the oldest service branch and is known as the Senior Service...

’s Commander in Chief, Admiral of the Fleet Sir George Callaghan
George Callaghan
Admiral of the Fleet Sir George Astley Callaghan GCB GCVO was a senior officer in the Royal Navy.-Naval career:...

, requested its production in 1914. Design work was carried out by Herbert Taylor at HMS Vernon Torpedo and Mine School
HMS Vernon (shore establishment)
HMS Vernon was a shore establishment or 'stone frigate' of the Royal Navy. Vernon was established on 26 April 1876 as the Royal Navy's Torpedo Branch and operated until 1 April 1996, when the various elements comprising the establishment were split up and moved to different commands.-Foundation...

 in Portsmouth
Portsmouth
Portsmouth is the second largest city in the ceremonial county of Hampshire on the south coast of England. Portsmouth is notable for being the United Kingdom's only island city; it is located mainly on Portsea Island...

, England, and the first effective depth charge, the "Type D", became available in January 1916.

Anti-submarine vessels initially carried only two depth charges, to be released from a chute at the stern of the ship. The first success was the sinking of U-68 off Kerry
County Kerry
Kerry means the "people of Ciar" which was the name of the pre-Gaelic tribe who lived in part of the present county. The legendary founder of the tribe was Ciar, son of Fergus mac Róich. In Old Irish "Ciar" meant black or dark brown, and the word continues in use in modern Irish as an adjective...

, Ireland, on 22 March 1916 by the Q-ship
Q-ship
Q-ships, also known as Q-boats, Decoy Vessels, Special Service Ships, or Mystery Ships, were heavily armed merchant ships with concealed weaponry, designed to lure submarines into making surface attacks. This gave Q-ships the chance to open fire and sink them...

 Farnborough.
HMS Farnborough
HMS Farnborough, also known as , was a Q-ship of the British Royal Navy that saw service in the First World War. Farnborough was a heavily armed merchant ship with concealed weaponry that was designed to lure submarines into making surface attacks. Farnborough sank two submarines in her service in...

  Germany became aware of the depth charge following unsuccessful attacks on U-67 on 15 April 1916, and U-69 on 20 April. UC-19
SM UC-19
SM UC-19 was a German Type UC II minelaying submarine or U-boat in the German Imperial Navy during World War I. The U-boat was ordered on 26 August 1915 and was launched on 15 March 1916...

 and UB-29
SM UB-29
SM UB-29 was a German Type UB II submarine or U-boat in the German Imperial Navy during World War I. The U-boat was ordered on 30 April 1915 and launched on 10 February 1916...

 were the only other submarines sunk by depth charges during 1916.

In support of the High Seas Fleet

In 1916 the German Navy again tried to use the U-boats to erode the Grand Fleet's numerical superiority; they staged operations to lure the Grand Fleet into a U-boat trap. Because the U-boats were much slower than the battle fleet, these operations required U-boat patrol lines to be set up in advance; then the battle fleet maneuvered to draw the Grand Fleet onto them.

Several of these operations were staged, in March and April 1916, but with no success. Ironically, the major fleet action which did take place, the Battle of Jutland
Battle of Jutland
The Battle of Jutland was a naval battle between the British Royal Navy's Grand Fleet and the Imperial German Navy's High Seas Fleet during the First World War. The battle was fought on 31 May and 1 June 1916 in the North Sea near Jutland, Denmark. It was the largest naval battle and the only...

, in May 1916, saw no U-boat involvement at all; the fleets met and engaged largely by chance, and there were no U-boat patrols anywhere near the battle area. A further series of operations, in August and October 1916, were similarly unfruitful, and the strategy was abandoned in favor of resuming commerce warfare.

The British were well aware of the risk of U-boat traps to the Grand Fleet, although they had no means of knowing where these might lay. However Jellicoe
John Jellicoe, 1st Earl Jellicoe
Admiral of the Fleet John Rushworth Jellicoe, 1st Earl Jellicoe, GCB, OM, GCVO was a British Royal Navy admiral who commanded the Grand Fleet at the Battle of Jutland in World War I...

 had developed a tactical response to the problem (which, in the event, was never tested). Faced with a German fleet that turned away, he would assume a submarine trap, and decline to follow, but would move at high speed to the flank, before deploying or opening fire; the aim of this would be to fight the battle away from the ground chosen by his enemy, and forcing any U-boats present to surface if they intended to follow.

Mediterranean waters

During 1916 the commerce war continued unabated in the Mediterranean. Allied countermeasures were largely ineffective; the complex arrangements for co-operation between the various navies meant a fragmented and unco-ordinated response, while the main remedy favored by the Allies for the U-boat menace, the Otranto Barrage
Otranto Barrage
The Otranto Barrage was an Allied naval blockade of the Otranto Straits between Brindisi in Italy and Corfu on the Albanian side of the Adriatic Sea in World War I. The blockade was intended to prevent the Austro-Hungarian Navy from escaping into the Mediterranean and threatening Allied operations...

, was of little value.

Just two U-boats were caught in the barrage in all the time it was in operation; meanwhile merchant shipping suffered huge losses. In 1916 the Allies lost 415 ships, of 1,045,058 GRT
Tonnage
Tonnage is a measure of the size or cargo carrying capacity of a ship. The term derives from the taxation paid on tuns or casks of wine, and was later used in reference to the weight of a ship's cargo; however, in modern maritime usage, "tonnage" specifically refers to a calculation of the volume...

, half of all Allied ships sunk in all theatres.

Eight of the top dozen U-boat aces served in the Pola flotilla, including the highest scoring commander of all, K/L Arnauld de la Perière.

American waters

In 1916 the Germans completed two submarine merchant vessels
Merchant submarine
A merchant submarine is a type of submarine intended for trade, and being without armaments, it is not considered a warship like most other types of submarines...

, to be used as blockade runner
Blockade runner
A blockade runner is usually a lighter weight ship used for evading a naval blockade of a port or strait, as opposed to confronting the blockaders to break the blockade. Very often blockade running is done in order to transport cargo, for example to bring food or arms to a blockaded city...

s. The aim was to use them to carry high value goods to neutral nations such as the U.S., which still maintained a strict neutrality, and was prepared to trade with Germany as with any other nation. The first of these vessels, Deutschland
German submarine Deutschland
Deutschland was a blockade-breaking German merchant submarine used during World War I. It was developed with private funds and operated by the North German Lloyd Line...

, sailed in summer 1916 and made a favorable impact on U.S. public opinion. She made a second equally successful voyage in autumn of that year. Her sister, Bremen
German submarine Bremen
Bremen was a blockade-breaking German merchant submarine of World War I. Developed with private funds and operated by the North German Lloyd Line, she was one of the first of seven U-151 class U-boats built and one of only two used as unarmed cargo submarines....

, was less fortunate; she disappeared on her maiden voyage, the cause of her loss unknown.

A less favorable impression was made by the cruise of U-53
SM U-53
SM U-53 was a German Type Mittel U U-boat of the Kaiserliche Marine during the First World War, one of the six forming the sub type 51.-Construction and commissioning:U-53 was ordered from Germaniawerft, Kiel in 1914 and launched in 1916...

  under K/L Hans Rose
Hans Rose
Lieutenant Commander Hans Rose was one of the most successful and highly decorated German U-boat commander in the Kaiserliche Marine during .Rose was one of the most respected and brave U-boat commanders and famous for his humanity and fairness in battle...

. After refuelling at Newport, Rhode Island
Newport, Rhode Island
Newport is a city on Aquidneck Island in Newport County, Rhode Island, United States, about south of Providence. Known as a New England summer resort and for the famous Newport Mansions, it is the home of Salve Regina University and Naval Station Newport which houses the United States Naval War...

, Rose raided Allied shipping off the coast of Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...

 and the United States. Although this was in international waters, and Rose scrupulously followed international law, the action was seen as an affront to the U.S., particularly when U.S. warships were forced to stand aside while merchant ships nearby were sunk.

Arctic waters

In autumn 1916, U-boats of the High Seas flotilla attacked shipping bound for Russia
Russia
Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...

. Five U-boats operated in the Barents Sea
Barents Sea
The Barents Sea is a marginal sea of the Arctic Ocean, located north of Norway and Russia. Known in the Middle Ages as the Murman Sea, the sea takes its current name from the Dutch navigator Willem Barents...

 between North Cape
North Cape, Norway
North Cape is a cape on the island of Magerøya in Northern Norway, in the municipality of Nordkapp. Its 307 m high, steep cliff is often referred to as the northernmost point of Europe, located at , 2102.3 km from the North Pole. However, the neighbouring point Knivskjellodden is actually...

 and the Kola inlet
Kola Bay
Kola Bay or Murmansk Fjord is a 57-km-long fjord of the Barents Sea that cuts into the northern part of the Kola Peninsula. It is up to 7 km wide and has a depth of 200 to 300 metres. The Tuloma and Kola Rivers discharge into the bay....

. Also, the two UE1-class minelaying boats laid minefields in the White Sea
White Sea
The White Sea is a southern inlet of the Barents Sea located on the northwest coast of Russia. It is surrounded by Karelia to the west, the Kola Peninsula to the north, and the Kanin Peninsula to the northeast. The whole of the White Sea is under Russian sovereignty and considered to be part of...

. These boats sank 34 ships (19 of them Norwegian) before winter ice closed the area for operations.

1917: Resumption of unrestricted submarine warfare

On 22 December 1916, Admiral von Holtzendorff
Henning von Holtzendorff
Henning von Holtzendorff was a German admiral during World War I who became famous for his Dec 1916 memo to Kaiser Wilhelm II about unrestricted submarine warfare against the United Kingdom...

 composed a memorandum which became the pivotal document for Germany's resumption of unrestricted U-boat warfare in 1917. Holtzendorff proposed breaking Britain's back by sinking 600,000 tons of shipping per month, based on a February 1916 study by Dr. Richard Fuss, who had postulated that if merchant shipping was sunk at such a rate, Britain would run out of shipping and be forced to sue for peace within 6 months, well before the Americans could act. Even if the "disorganized and undisciplined" Americans did intervene, Holtzendorff assured the Kaiser, "I give your Majesty my word as an officer, that not one American will land on the Continent."

On 9 January 1917, the Kaiser met with Chancellor Bethmann-Hollweg and military leaders at Schloss Pless
Castle in Pszczyna
Castle in Pszczyna is a classical-style palace in Pszczyna. Constructed as a castle in 13th century or earlier, in a gothic style, it was rebuilt in renaissance style in 17th century, in baroque in 18th century and classicist in 19th century; the classicist modernization transformed the castle...

 to discuss measures to resolve Germany's increasingly grim war situation; its military campaign in France had bogged down, and with Allied divisions outnumbering German ones by 190 to 150, there was a real possibility of a successful Allied offensive. Meanwhile, the German navy was bottled up in its home port of Kiel, and the British blockade had caused a food scarcity that was in turn causing deaths due to malnutrition. The military staff urged the Kaiser to unleash the submarine fleet on shipping travelling to Britain, Hindenburg advising the Kaiser that "The war must be brought to an end by whatever means as soon as possible." On 31 January, the Kaiser duly signed the order for unrestricted submarine warfare to resume effective 1 February; Bethmann-Hollweg, who had opposed the decision, said "Germany is finished".

On 27 January, Admiral Beatty
David Beatty, 1st Earl Beatty
Admiral of the Fleet David Richard Beatty, 1st Earl Beatty, GCB, OM, GCVO, DSO was an admiral in the Royal Navy...

 observed that "The real crux lies in whether we blockade the enemy to his knees, or whether he does the same to us."

Germany had 105 submarines ready for action on 1 February: 46 in the High Seas Fleet; 23 in Flanders; 23 in the Mediterranean; 10 in the Baltic; and 3 at Constantinople. Fresh construction ensured that, despite losses, at least 120 submarines would be available for the rest of 1917. The campaign was initially a great success, nearly 500,000 tons of shipping being sunk in both February and March, and 860,000 tons in April, when Britain's supplies of wheat shrank to 6 weeks worth. In May losses exceeded 600,000 tons, and in June 700,000. Germany had lost only 9 submarines in the first three months of the campaign.

On 3 February, in response to the new submarine campaign, President Wilson severed all diplomatic relations with Germany, and the U.S. Congress declared war on 6 April.

Allied response

The new policy of unrestricted submarine warfare was initially a success. In January 1917, prior to the campaign, Britain lost 49 ships; in February, after it opened, 105; and in March, 147. In March a full 25% of all Britain-bound shipping was sunk.

The British Admiralty failed to respond effectively to the German offensive. Despite the proven success of troop convoys earlier in the war, the Channel convoys between England and France, and the Dutch, French, and Scandinavian convoys in the North Sea, they initially refused to consider widespread convoying or escorting. Convoying imposed severe delays on shipping, and was believed to be an own goal, amounting to a loss of carrying capacity greater than the loss inflicted by the U-Boats. It was disliked by both merchant and naval captains, and derided as a defensive measure. It was not until 27 April that the Admiralty endorsed the convoy system, the first convoy sailing from Gibraltar on 10 May.

In April, US Rear Admiral William Sims
William Sims
William Sowden Sims was an admiral in the United States Navy who sought during the late 19th and early 20th centuries to modernize the Navy. During World War I he commanded all United States naval forces operating in Europe...

 arrived in London as US Naval Liaison. He was dismayed to be informed by the Admiralty that Germany would win the war if its submarines went unchecked, and cabled Washington to have USN destroyers despatched to Queenstown
Cobh
Cobh is a seaport town on the south coast of County Cork, Ireland. Cobh is on the south side of Great Island in Cork Harbour. Facing the town are Spike Island and Haulbowline Island...

, Ireland, from where they were to patrol to the west.

As merchantmen from Allied countries were sunk, Brazilian ships took over routes that had been vacated. However, this led the Brazilian vessels into waters patrolled by U-boats. When coupled with Germany's policy of unrestricted submarine warfare, the result was that Brazilian ships were soon lost, which drove the country closer to declaring war on the Central Powers.

In May and June a regular system of transatlantic convoys were established, and after July the monthly losses never exceeded 500,000 tons, although they remained above 300,000 tons for the remainder of 1917.
Convoying was an immediate success; on whichever routes it was introduced it resulted in a drop in shipping losses, with the U-boats seeking out easier prey. It also brought warships escorting the convoys in contact with attacking U-boats, leading to an increase in U-boats destroyed.
German submarine losses were between 5 and 10 each month, and they soon realized the need to increase production, even at the expense of building surface warships. However, production was delayed by labour and material shortages.

1918: The last year

At the end of 1917 Allied shipping losses stood at over 6 million GRT for the year overall.
However monthly shipping losses had dropped to around 300,000 GRT per month, and never rose to the levels suffered in spring 1917.
With the establishment of a comprehensive convoy system, Allied shipping losses fell to non-critical levels, while U-boat losses increased alarmingly. From 48 boats lost in the years up to February 1917, a further 61 were lost by the end of the year.

The logical response to the convoy system, which concentrated forces for the defence, was to similarly concentrate the attacking force. The U-boat arm did not succeed in World War I in developing such a response. Just one attempt was made to operate a group, to mount a pack attack on any convoy encountered; 6 U-boats sailed in May 1918 as a group, commanded by K/L Rucker in U-103.
They encountered several home-bound convoys and succeeded in sinking 3 ships, but at the loss of 2 of their number, including U-103, which was rammed by the troopship Olympic
RMS Olympic
RMS Olympic was the lead ship of the Olympic-class ocean liners built for the White Star Line, which also included Titanic and Britannic...

. Rucker had found it next to impossible to exercise control from his position at sea, and the loss ratio discouraged any further experiments.

U-cruisers

Late in the war, the German high command decided to take the submarine war to the coast of the US, using the large Type U-151 U-boat
German Type U 151 submarine
Type U 151 U-boats were a class of large, long-range submarines constructed during World War I by the Kaiserliche Marine.-Background:In addition to the cargo-carrying submarine Deutschland, six further large cargo submarines were ordered, originally designed to ship material to and from locations...

s. The Type U-151 carried 18 torpedoes and two 105 mm deck guns, and had a range of around 25000 nautical miles (46,300 km). Seven had been built in 1916, originally as large merchant U-boat
Merchant submarine
A merchant submarine is a type of submarine intended for trade, and being without armaments, it is not considered a warship like most other types of submarines...

s for shipping material to and from locations otherwise denied German surface ship
Surface ship
A surface ship is any type of naval ship that is confined to the surface of the sea. The term is primarily used to mean any modern vessel type that is not a submarine; although a "surface ship" may range in size from a cutter to an aircraft carrier, the weapons and tactics have some commonality,...

s, such as the United States, and 6 were refitted for war duty in 1917. They were the largest U-boats of World War I.

American campaign

U-151 departed Kiel on 14 April 1918 commanded by Korvettenkapitän Heinrich von Nostitz und Jänckendorff, her mission to attack American shipping. She arrived in Chesapeake Bay
Chesapeake Bay
The Chesapeake Bay is the largest estuary in the United States. It lies off the Atlantic Ocean, surrounded by Maryland and Virginia. The Chesapeake Bay's drainage basin covers in the District of Columbia and parts of six states: New York, Pennsylvania, Delaware, Maryland, Virginia, and West...

 on 21 May where she laid mines off the Delaware capes, and cut the submerged telegraph cables which connected New York with Nova Scotia
Nova Scotia
Nova Scotia is one of Canada's three Maritime provinces and is the most populous province in Atlantic Canada. The name of the province is Latin for "New Scotland," but "Nova Scotia" is the recognized, English-language name of the province. The provincial capital is Halifax. Nova Scotia is the...

. On 25 May she stopped three US schooners off Virginia, took their crews prisoner, and sank the three ships by gunfire. On 2 June 1918, known to some historians as "Black Sunday", U-151 sank six US ships and damaged two others off the coast of New Jersey in the space of a few hours. The next day the tanker Herbert L. Pratt struck a mine previously laid by U-151 in the area but was later salvaged. Only 13 people died in the seven sinkings, their deaths caused by a capsized lifeboat. She returned to Kiel on 20 July 1918 after a 94-day cruise in which she had covered a distance of 10915 mi (17,565.9 km), sunk 23 ships totalling 61,000 tons, and had laid mines responsible for the sinking of another 4 vessels.

Encouraged by the success of U-151, U-156, U-117
SM U-117
SM U-117 was a Type UE II long-range minelayer submarine of the Imperial German Navy. It was laid down in 1917 at Hamburg, Germany, by Aktiengesellschaft Vulcan and launched on 10 December 1917. It was commissioned in the Imperial German Navy on 28 March 1918 with Kapitänleutnant Otto Dröscher in...

, and the large Type 139
German Type U 139 submarine
U-139, originally designated "Project 46", was a class of large, long-range U-boats built during World War I by the Kaiserliche Marine.-Description:Three large U-cruisers, designated Type 139, were ordered from Germaniawerft, Kiel, in August 1916...

 U-cruiser U-140
SM U-140
SM U-140 was one of the 329 submarines serving in the Imperial German Navy in World War I.U-140 was engaged in the naval warfare and took part in the First Battle of the Atlantic.-References:...

 were despatched on similar missions, but the US Navy was now ready for them, and the hunting was not as good. U-156 was lost with all hands on the return voyage when she struck a mine off Bergen, Norway, on 25 September 1918. Another trio of long-range submarines, U-155, U-152
SM U-152
SM U-152 was a German Type U 151 submarine of the Kaiserliche Marine during World War I.Built at Hamburg, the submarine was commissioned in October 1917...

, and U-cruiser U-139
SM U-139
SM U-139 was the lead ship of her class, one of the submarines serving in the Imperial German Navy in World War I. She was commissioned on 18 May 1918 under the command of Lothar von Arnauld de la Perière, who named the submarine Korvettenkapitän Schweiger, after Walther Schwieger, who had sunk...

 were making their way across the Atlantic in November 1918 when the war ended.

A few of the U-cruisers also made long voyages south to the Azores and the African coast, where they operated generally unmolested against shipping operating in the area, though one, U-154
SM U-154
SM U-154 was one of the 329 submarines serving in the Imperial German Navy in World War I.U-154 was engaged in the naval warfare and took part in the First Battle of the Atlantic....

, was torpedoed by the British submarine HMS E35
HMS E35
HMS E35 was a British E class submarine built by John Brown, Clydebank. She was laid down on 20 May 1916 and was commissioned on 14 July 1917.-Service history:...

 off the coast of Portugal in May 1918.

Final countermeasures

By 1918 the Allied anti-submarine measures had continued to become more effective.

Aircraft began to play an increasingly effective role in patrolling large areas quickly. While they had little effect when attacking (only one U-boat was confirmed as sunk by air attack) the presence of aircraft forced the U-boat to dive, becoming blind and immobile, or risk the air patrol summoning hunting warships to the scene. During 1918 no convoy escorted by air patrol lost a ship, and U-boats were forced increasingly to operate at night or beyond aircraft range.

In 1918 the USN embarked on a mammoth scheme to create a barrage across the routes exiting the North Sea. The North Sea Mine Barrage saw the laying of over 70,000 mines during the summer of 1918. From September to November 1918 6 U-boats were sunk by this measure.

The RN also developed the R class submarine, designed as a hunter-killer vessel, with a high underwater speed and sophisticated hydrophone system. These came too late to see action, however, and no successes were recorded by them.

By the end of the year, Allied shipping losses were 2¾ million GRT for the year overall; The U-boat Arm lost 69 boats in 1918, its worst year.

United States Navy in the Mediterranean Sea

During the Great War United States Navy warships were deployed to both the Atlantic and Mediterranean with the primary objective of fighting German submarines and escorting convoys. Many contacts were made in the Mediterranean though only one decisive action occurred. An American auxiliary cruiser heavily damaged a U-boat during the Action of 4 April 1918
Action of 4 April 1918
The Action of 4 April 1918 was a naval action fought in the Atlantic Ocean during World War I. An unknown Kaiserliche Marine U-boat attacked three armed transports of the United States Army and Navy, but failed to damage the American ships before she was sunk.-Action:On April 4, 1918, three armed...

. As result the Germans sailed directly for Spain where they scuttled their boat. American submarine chasers also engaged in one battle
Battle of Durazzo (1918)
The Second Battle of Durazzo, or the Bombardment of Durazzo was a naval battle fought in the Adriatic Sea during World War I. A large Allied fleet led by the Regia Marina attacked the enemy held naval base at Durazzo, Albania. The fleet destroyed the Austro-Hungarian shore defenses and skirmished...

 against Austro-Hungarian forces during the war. Though their participation in the conflict was intended as a counter-submarine effort, they were engaged by enemy shore batteries, charted a path through a minefield and helped sink two Austro-Hungarian destroyers at the naval base of Durazzo, Albania
Albania
Albania , officially known as the Republic of Albania , is a country in Southeastern Europe, in the Balkans region. It is bordered by Montenegro to the northwest, Kosovo to the northeast, the Republic of Macedonia to the east and Greece to the south and southeast. It has a coast on the Adriatic Sea...

.

Japanese participation

Beginning in April 1917, Japan, an ally of the United Kingdom, sent a total of 14 destroyers to the Mediterranean with cruiser flagships which were based at Malta and played an important part in escorting convoys to guard them against enemy submarines. The Japanese ships were very effective in patrol and anti-submarine activity. However, of the 9 Austro-Hungarian navy submarines lost to enemy action, 5 were sunk by Italian navy units (U-13, U-10, U-16, U-20, and U-23), 1 by Italian and French units (U-30), 1 by Royal Navy units (U-3), while none were sunk by the Japanese navy, which lost one destroyer (Japanese destroyer Sakaki, torpedoed by U-27).

Brazilian participation

On 21 December 1917 the British government requested that a Brazilian naval force of light cruisers be placed under Royal Navy control and a squadron comprising the cruisers Rio Grande do Sul and Bahia, the destroyers Paraíba, Rio Grande do Norte, Piauí, and Santa Catarina, and the support ship Belmonte and the ocean-going tug Laurindo Pitta was formed, designated the Divisão Naval em Operações de Guerra ("Naval Division in War Operations"). The DNOG sailed on 31 July 1918 from Fernando de Noronha
Fernando de Noronha
Fernando de Noronha is an archipelago of 21 islands and islets in the Atlantic Ocean, offshore from the Brazilian coast. The main island has an area of and had a population of 3,012 in the year 2010...

 for Sierra Leone
Sierra Leone
Sierra Leone , officially the Republic of Sierra Leone, is a country in West Africa. It is bordered by Guinea to the north and east, Liberia to the southeast, and the Atlantic Ocean to the west and southwest. Sierra Leone covers a total area of and has an estimated population between 5.4 and 6.4...

, arriving at Freetown on 9 August, and sailing onwards to its new base of operations, Dakar
Dakar
Dakar is the capital city and largest city of Senegal. It is located on the Cap-Vert Peninsula on the Atlantic coast and is the westernmost city on the African mainland...

, on 23 August. On the night of the 25 August the division believed it had been attacked by a U-boat when the auxiliary cruiser Belmonte sighted a torpedo track. The purported submarine was depth-charged, fired on, and reportedly sunk by the Rio Grande do Norte, but the sinking was never confirmed.

The DNOG patrolled the Dakar-Cape Verde
Cape Verde
The Republic of Cape Verde is an island country, spanning an archipelago of 10 islands located in the central Atlantic Ocean, 570 kilometres off the coast of Western Africa...

-Gibraltar
Gibraltar
Gibraltar is a British overseas territory located on the southern end of the Iberian Peninsula at the entrance of the Mediterranean. A peninsula with an area of , it has a northern border with Andalusia, Spain. The Rock of Gibraltar is the major landmark of the region...

 triangle, which was suspected to be used by U-boats waiting on convoys, until 3 November 1918 when it sailed for Gibraltar to begin operations in the Mediterranean, with the exception of the Rio Grande do Sul, Rio Grande do Norte, and Belmonte. The Division arrived at Gibraltar on 10 November; while passing through the Straits of Gibraltar, they mistook three USN subchasers for U-boats but no damage was caused.

The end

By 1918, U-boat losses had reached unacceptable levels, and the morale of their crews had drastically deteriorated; by the autumn it became clear that the Central Powers could not win the war.

The Allies insisted that an essential precondition of any armistice was that Germany surrender all her submarines, and on 24 October 1918 all German U-boats were ordered to cease offensive operations and return to their home ports. The Allies stipulated that all seaworthy submarines were to be surrendered to them and those in shipyards be broken up. The last significant role played by U-boats in World War I was the suppression of the German naval mutiny
Wilhelmshaven mutiny
The Kiel mutiny was a major revolt by sailors of the German High Seas Fleet on 3 November 1918. The revolt triggered the German revolution which was to sweep aside the monarchy within a few days. It ultimately led to the end of the First World War and to the establishment of the Weimar Republic.-...

 that same month, when they stood ready to "fire without warning on any vessel flying the red flag".

Allied and Neutral Tonnage sunk by submarines in World War I

Month 1914 1915 1916 1917 1918
January 47,981 81,259 368,521 306,658
February 59,921 117,547 540,006 318,957
March 80,775 167,097 593,841 342,597
April 55,725 191,667 881,027 278,719
May 120,058 129,175 596,629 295,520
June 131,428 108,855 687,507 255,587
July 109,640 118,215 557,988 260,967
August 62,767 185,866 162,744 511,730 283,815
September 98,378 151,884 230,460 351,748 187,881
October 87,917 88,534 353,660 458,558 118,559
November 19,413 153,043 311,508 289,212 17,682
December 44,197 123,141 355,139 399,212
Total 312,672 1,307,996 2,327,326 6,235,878 2,666,942


Grand Total 12,850,815 gross tons

Unrestricted submarine warfare was resumed in February 1917 and the British began full-scale convoying in September 1917. The heaviest losses were suffered in April 1917 when a record 881,027 tons were sunk by the U-boats.

During World War I nearly 5,000 merchant ships had been sunk by u-boats, with the loss of 15,000 Allied sailors lives.

German Submarine Force 1914–1918

1914 1915 1916 1917 1918
On hand 24 29 54 133 142
Gains 10 52 108 87 70
Battle losses 5 19 22 63 69
Other losses 8 7 15 9??
Years end 29 54 133 142 134

  • Total operational boats: 351
  • Total sunk in combat : 178 (50%)
  • Other losses: 39 (11%)
  • Completed after Armistice: 45
  • Surrendered to Allies: 179
  • Men lost in Uboats: 5,000 killed

See also

  • Atlantic U-boat Campaign (World War I)
    Atlantic U-boat Campaign (World War I)
    The Atlantic U-boat Campaign of World War I was the naval campaign fought by German U-boats in Atlantic waters, that is, the seas around the British Isles, the North Sea, and the coast of France. Initially directed against the British Grand Fleet, later it was extended to include action against...

  • Mediterranean U-boat Campaign (World War I)
    Mediterranean U-boat Campaign (World War I)
    The Mediterranean U-boat Campaign in the Mediterranean Sea was fought by Austria-Hungary and German Empire against the Allies during World War I...


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