Mediterranean U-boat Campaign (World War I)

The Mediterranean U-boat Campaign in the Mediterranean Sea

Mediterranean Sea

The Mediterranean Sea is a sea connected to the Atlantic Ocean surrounded by the Mediterranean region and almost completely enclosed by land: on the north by Anatolia and Europe, on the south by North Africa, and on the east by the Levant...

was fought by Austria-Hungary

Austria-Hungary

Austria-Hungary , more formally known as the Kingdoms and Lands Represented in the Imperial Council and the Lands of the Holy Hungarian Crown of Saint Stephen, was a constitutional monarchic union between the crowns of the Austrian Empire and the Kingdom of Hungary in...

and 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...

(with some support by the Ottoman Empire

Ottoman Empire

The Ottoman EmpireIt was usually referred to as the "Ottoman Empire", the "Turkish Empire", the "Ottoman Caliphate" or more commonly "Turkey" by its contemporaries...

) against the Allies during 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...

. It was characterised by the ability of the Central Powers

Central Powers

The Central Powers were one of the two warring factions in World War I , composed of the German Empire, the Austro-Hungarian Empire, the Ottoman Empire, and the Kingdom of Bulgaria...

to raid with near impunity during the first years of the war, causing substantial shipping losses, until the introduction of the convoy

Convoy

A convoy is a group of vehicles, typically motor vehicles or ships, traveling together for mutual support and protection. Often, a convoy is organized with armed defensive support, though it may also be used in a non-military sense, for example when driving through remote areas.-Age of Sail:Naval...

system allowed the Allies to drastically cut their losses from 1917 on.

1914: Initial stages

At the outbreak of World War I , with Italy

Italy

Italy , officially the Italian Republic languages]] under the European Charter for Regional or Minority Languages. In each of these, Italy's official name is as follows:;;;;;;;;), is a unitary parliamentary republic in South-Central Europe. To the north it borders France, Switzerland, Austria and...

’s decision to remain neutral, the naval strength of the Central Powers

Central Powers

The Central Powers were one of the two warring factions in World War I , composed of the German Empire, the Austro-Hungarian Empire, the Ottoman Empire, and the Kingdom of Bulgaria...

was represented by the navy of the Austro-Hungarian Empire, the KuK Kriegsmarine

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....

, whose only access to the sea was through the Adriatic coast. The Entente powers moved swiftly to blockade the Adriatic, sending a fleet to take station at the straits of Otranto.

The initial phase of the U-boat campaign in the Mediterranean comprised the actions by the KuKs U-boat force against the French. At the start of hostilities, the KuK had seven U-boats in commission; five operational, two 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, torpedoed the French battleship

Battleship

A battleship is a large armored warship with a main battery consisting of heavy caliber guns. Battleships were larger, better armed and armored than cruisers and destroyers. As the largest armed ships in a fleet, battleships were used to attain command of the sea and represented the apex of a...

, Admiral Lapeyrere's flagship. She was saved from sinking, but was forced to retire with a damaged bow. This setback dissuaded the French capital ships from penetrating too far into the Adriatic. On 27 April 1915, sank the French cruiser , 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.

Operations at the Dardanelles

In April 1915, the Imperial 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-boat sent——achieved initial success, sinking the Royal Navy predreadnought battleships and 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. In addition, the Germans dispatched a number of UB and UC Type boats; these were sent in sections by rail to Pola

Pula

Pula is the largest city in Istria County, Croatia, situated at the southern tip of the Istria peninsula, with a population of 62,080 .Like the rest of the region, it is known for its mild climate, smooth sea, and unspoiled nature. The city has a long tradition of winemaking, fishing,...

where they were assembled for transit to Constantinople

Constantinople

Constantinople was the capital of the Roman, Eastern Roman, Byzantine, Latin, and Ottoman Empires. Throughout most of the Middle Ages, Constantinople was Europe's largest and wealthiest city.-Names:...

. One was lost, but by the end of 1915 the Germans had established a force of seven U-boats at Constantinople, misleadingly named the Mediterranean U-Boat Division

Constantinople Flotilla

The Constantinople flotilla was an Imperial German Navy formation set up to prosecute the U-boat campaign against Allied shipping in the Mediterranean and the Black Sea in support of Germany’s ally, the Ottoman Empire...

The Pola flotilla

At the same time, the Germans determined to establish a force in the Adriatic to open the commerce war against Allied trade in the Mediterranean.

By the end of June 1915, the Germans had assembled a further three pre-fabricated 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

Pula

in Istria

Istria

Istria , formerly Histria , is the largest peninsula in the Adriatic Sea. The peninsula is located at the head of the Adriatic between the Gulf of Trieste and the Bay of Kvarner...

, two of them intended for transfer to the Austrian Navy. They were also assembling three 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. However, the UB submarines were hindered by their short operational range and the Dardanelles currents, and in July U-21—the only U-boat with a decent operating range—was damaged by a mine and confined to Constantinople.

On 21 July, the ocean-going submarines and were detached from service in the Baltic

Baltic Sea

The Baltic Sea is a brackish mediterranean sea located in Northern Europe, from 53°N to 66°N latitude and from 20°E to 26°E longitude. It is bounded by the Scandinavian Peninsula, the mainland of Europe, and the Danish islands. It drains into the Kattegat by way of the Øresund, the Great Belt and...

and sent to Cattaro (in present-day Montenegro

Montenegro

Montenegro Montenegrin: Crna Gora Црна Гора , meaning "Black Mountain") is a country located in Southeastern Europe. It has a coast on the Adriatic Sea to the south-west and is bordered by Croatia to the west, Bosnia and Herzegovina to the northwest, Serbia to the northeast and Albania to the...

), the Germans deciding to make use of Austrian bases rather than Constantinople, since there were better supply and repair facilities in the Adriatic and it avoided submarines having to negotiate the dangerous passage through the Dardanelles. In August, and joined the German Flotilla

Pola Flotilla

The Pola flotilla was an Imperial German Navy formation set up to prosecute the U-boat campaign against Allied shipping in the Mediterranean during the First World War in support of Germany’s ally, the Austro-Hungarian Empire...

stationed at Cattaro, following pleas from the German military attaché in Constantinople, who reported that the Royal Navy's close naval support was inflicting heavy losses on Turkish forces at the Gallipoli beachheads.

The war on commerce

The Mediterranean was an attractive theatre of operations for the German Admiralstab
German Imperial Admiralty Staff
The German Imperial Admiralty Staff was a military institution established in 1899 under the direct authority and command of the German Emperor, Kaiser Wilhelm II for managing the German Imperial Navy...

s war on Allied commerce; 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 the northern-hemisphere autumn and winter, when poor weather hampered naval operations in the Atlantic and the North Sea. 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 U.S. vessels, and fewer American citizens travelled the waters.

The German campaign in the Mediterranean is generally agreed to have properly begun 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 63848 LT (64,872.8 t). It was decided the same month that further reinforcements were called for, and a further large U-boat——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 155882 LT (158,383.9 t). The total in December fell to 17 ships (73741 LT (74,924.5 t)) which was still over ½ the total tonnage sunk in all theaters of operation at the time.

The Ancona incident

In November 1915, U-38—sailing under the Austrian flag and commanded by Kapitanleutnant (K/L) Max Valentiner

Max Valentiner

Captain Christian August Max Ahlmann Valentiner was a German U-boat commander during World War I.He was the third highest-scoring U-boat commander of the war, and was awarded the Pour le Mérite, the highest Prussian military order until the end of the war, for his achievements.He was also branded...

—caused a diplomatic incident when she sank the Italian passenger liner off the coast of Tunisia

Tunisia

Tunisia , officially the Tunisian RepublicThe long name of Tunisia in other languages used in the country is: , is the northernmost country in Africa. It is a Maghreb country and is bordered by Algeria to the west, Libya to the southeast, and the Mediterranean Sea to the north and east. Its area...

. Ancona—bound from Messina to New York

New York

New York is a state in the Northeastern region of the United States. It is the nation's third most populous state. New York is bordered by New Jersey and Pennsylvania to the south, and by Connecticut, Massachusetts and Vermont to the east...

—was fully booked and over 200 lives were lost, including nine Americans. Coming as it did six months after the sinking of the British liner off Ireland, the Ancona incident added to a growing outrage in the U.S. over unrestricted submarine warfare, and U.S. Secretary of State 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...

despatched a sternly-worded protest to Vienna.

In December 1915, Valentiner caused further outrage when he sank the passenger liner without warning. 343 lives were lost.

In a further incident in March 1916, the German minelayer was blown up by its own mines while laying a mine field off Taranto

Taranto

Taranto is a coastal city in Apulia, Southern Italy. It is the capital of the Province of Taranto and is an important commercial port as well as the main Italian naval base....

harbor. Italian divers inspected the wreck and established its identity. The knowledge that Germany—technically their ally—was assiduously mining their naval bases was a contributing factor in Italy’s decision in May 1916 to declare war on Germany.

1916: The commerce war continues

During 1916, the commerce war continued unabated. 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 was to establish an anti-submarine barrier across the Straits of Otranto, 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...

. This too was ineffective; the Straits were too wide and deep for such a barrage to be successful, and consumed a huge effort and tied up many of the patrol vessels the Allies possessed. It also acted as a target for surface attacks, being the target for a number of raids by KuK forces. Just two U-boats were caught in the barrage in all the time it was in operation; meanwhile the merchant ships continued to suffer huge losses. In 1916, the Allies lost 415 ships, of 1045058 LT (1,061,831.2 t), ½ of all allied ships sunk in all theaters.

Eight of the top 12 U-boat aces served in the Pola flotilla—including the highest scoring commander of all, K/L Arnauld de la Perière.

1917: Unrestricted submarine warfare

In January 1917, following the German decision to resume unrestricted submarine warfare, Foreign Secretary Arthur Zimmermann

Arthur Zimmermann

Arthur Zimmermann was State Secretary for Foreign Affairs of the German Empire from November 22, 1916, until his resignation on August 6, 1917. His name is associated with the Zimmermann Telegram during World War I...

led a delegation to Vienna to secure the collaboration of Austria-Hungary. Grand Admiral Haus wholly supported the proposal, but Foreign Minister Count Ottokar Czernin had misgivings, as did the emperor, Charles I of Austria. Haus and the German delegates finally won the debate, partly by listing several instances where Allied submarines had sunk unarmed Austro-Hungarian ships in the Adriatic. The negotiations over the terms of the new Mediterranean submarine campaign were aided by the fact that Italy had declared war on Germany on 28 August 1916, making it no longer necessary for German U-boats to masquerade as Austrian vessels when attacking Italian shipping.

Shipping losses to U-boats reached a peak in April 1917, when the Central Powers had 28 boats operating, with as many as 10 at sea at any one time. While not a single submarine was sunk, they caused 94 ship losses in that one month, and severely endangered and delayed shipping. However, by that time, the Italian Navy had instituted convoy operations, with the British following on the Alexandria-Malta route in May 1917.

Japanese participation

Beginning in April 1917, Japan, an ally of Great Britain, 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 nine Austro-Hungarian navy submarines lost to enemy action, five were sunk by Italian navy units (U-13, U-10, U-16, U-20, and U-23), one by Italian and French units (U-30), one by Royal Navy units (U-3), while none were sunk by the Japanese navy, which lost one destroyer .

1918: Final stages

Although convoys had been introduced between Malta

Malta

and Alexandria

Alexandria

Alexandria is the second-largest city of Egypt, with a population of 4.1 million, extending about along the coast of the Mediterranean Sea in the north central part of the country; it is also the largest city lying directly on the Mediterranean coast. It is Egypt's largest seaport, serving...

in May 1917, the Allies were unable to introduce a comprehensive system until later in the year. The number of routes, and divided responsibilities made this complicated, while a continued belief in offensive measures, such as the Otranto barrage, kept up a shortage of escort ships elsewhere. Throughout the year U-boats were still able to find and sink ships sailing independently. By 1918, however, the U-boats successes began to drop. In January 1918, German U-boats sank 103738 LT (105,403 t) and the Austrians sank a further 20020 LT (20,341.3 t) while two Pola boats were sunk.

Allied losses continued to fall during the year, while U-boat losses mounted. In May 1918, Allied losses dropped below 100000 LT (101,605 t) and did not rise above this again, while the Pola flotilla lost four boats, its worst month ot the war.

Karl Dönitz

Karl Dönitz

Karl Dönitz was a German naval commander during World War II. He started his career in the German Navy during World War I. In 1918, while he was in command of , the submarine was sunk by British forces and Dönitz was taken prisoner...

—who would go on to command the German U-boat force in World War II, was commander of UB-68, operating in the Mediterranean. On 4 October, this boat was sunk by British forces and Dönitz was taken prisoner on the island of Malta.

By October 1918, the end of the campaign, Allied losses for the year stood at 761000 LT (773,214.1 t). The Pola flotilla had lost 11 Boats, and the KuK a further 3. In October, the Central Powers

Central Powers

The Central Powers were one of the two warring factions in World War I , composed of the German Empire, the Austro-Hungarian Empire, the Ottoman Empire, and the Kingdom of Bulgaria...

were on the verge of collapse; Bulgaria and the Ottomans had sued for peace, and the Austrians were about to do the same. The Germans elected to abandon the Mediterranean; nine U-boats sailed from their bases on the Adriatic to return to Germany and a further 10 boats were scuttled. Two ships—Mercia and Surada—were torpedoed on the way, the last Allied ships to be sunk in the Mediterranean, and three U-boats were attacked. was damaged and forced to run for Barcelona

Barcelona

Barcelona is the second largest city in Spain after Madrid, and the capital of Catalonia, with a population of 1,621,537 within its administrative limits on a land area of...

, where she was interned
was destroyed. The last action of the Mediterranean force came on 9 November 1918, just two days before the Armistice: torpedoed and sank the British battleship off Cape Trafalgar

Cape Trafalgar

Cape Trafalgar is a headland in the Province of Cádiz in the south-west of Spain. It lies on the shore of the Atlantic Ocean, northwest of the Strait of Gibraltar...

Bases and areas of operations

Most of the German (and all of the Austro-Hungarian) U-boats operated out of the Adriatic, with their main base at Cattaro. Another German U-boat base was located at Constantinople

Constantinople

in the Ottoman Empire

Ottoman Empire

The Ottoman EmpireIt was usually referred to as the "Ottoman Empire", the "Turkish Empire", the "Ottoman Caliphate" or more commonly "Turkey" by its contemporaries...

. The U-boats also laid minefields, spread between such different locations like outside of Toulon

Toulon

Toulon is a town in southern France and a large military harbor on the Mediterranean coast, with a major French naval base. Located in the Provence-Alpes-Côte-d'Azur region, Toulon is the capital of the Var department in the former province of Provence....

, France to near Alexandria

Alexandria

, Egypt.

Table

Date	Ships sunk (KuK)	Ships sunk (Pola)	Tonnage	U-boats destroyed (KuK)	U-boats destroyed (Pola)
1914	?	n/a	n/a	none	n/a
1915	?	102	350,853	2	none
1916	?	415	1,045,058	2	1
1917	?	(not recorded)	1,514,050	2	2
1918	?	325	761,060	3	10

1914: Initial stages

Operations at the Dardanelles

The Pola flotilla

The war on commerce

The Ancona incident

1916: The commerce war continues

1917: Unrestricted submarine warfare

Japanese participation

1918: Final stages

Bases and areas of operations

Table

See also