SM U-21 (Germany)
SM U-21 was one of the most famous 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 to serve in the Imperial German Navy
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...

 in 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...

. She was the first submarine
A submarine is a watercraft capable of independent operation below the surface of the water. It differs from a submersible, which has more limited underwater capability...

 to sink a ship with a self-propelled 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...

. She also sank the British 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...

. U-21 survived the war and sank while under tow by a British warship in 1919.

Outbreak of War

Ordered in 1911 and built by the Kaiserliche Werft at the Imperial shipyard in Danzig, U-21 was commissioned in 1913. In August 1914 at the outbreak of war, she was stationed at 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...

, as part of the Third Half Flotilla (Second Flotilla). She was commanded by Otto Hersing, who stayed with her until the end of the war. On her third war patrol, she sighted 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...

 scout cruiser
Scout cruiser
A scout cruiser was a type of warship of the early 20th Century, which were smaller, faster, more lightly armed and armoured than protected cruisers or light cruisers, but larger than contemporary destroyers...

, HMS Pathfinder
HMS Pathfinder (1904)
HMS Pathfinder was the lead ship of the Pathfinder class scout cruisers, and was the first ship ever to be sunk by a torpedo fired by submarine . She was built by Cammell Laird, Birkenhead, launched on 16 July 1904, and commissioned on 18 July 1905...

 off the coast of St Abbs Head in Scotland
Scotland is a country that is part of the United Kingdom. Occupying the northern third of the island of Great Britain, it shares a border with England to the south and is bounded by the North Sea to the east, the Atlantic Ocean to the north and west, and the North Channel and Irish Sea to the...

, on 5 September 1914. A single torpedo hit the cruiser's hull causing a boiler
A boiler is a closed vessel in which water or other fluid is heated. The heated or vaporized fluid exits the boiler for use in various processes or heating applications.-Materials:...

 explosion which in turn ignited the ship's magazine
Magazine (artillery)
Magazine is the name for an item or place within which ammunition is stored. It is taken from the Arabic word "makahazin" meaning "warehouse".-Ammunition storage areas:...

. Pathfinder sank within four minutes and only 18 of her crew of 268 survived. This was the first ship to be sunk by a submarine-launched self-propelled torpedo - the USS Housatonic
USS Housatonic (1861)
The first USS Housatonic was a screw sloop-of-war of the United States Navy, named for the Housatonic River of New England which rises in Berkshire County, Massachusetts, and flows southward into Connecticut before emptying into Long Island Sound a little east of Bridgeport, Connecticut...

 had been sunk in 1864 with a spar torpedo
Spar torpedo
A spar torpedo is a weapon consisting of a bomb placed at the end of a long pole, or spar, and attached to a boat. The weapon is used by running the end of the spar into the enemy ship. Spar torpedoes were often equipped with a barbed spear at the end, so it would stick to wooden hulls...

, a simple charge fixed to a pole. U-21 was also the first U-boat to enter the Irish Sea
Irish Sea
The Irish Sea separates the islands of Ireland and Great Britain. It is connected to the Celtic Sea in the south by St George's Channel, and to the Atlantic Ocean in the north by the North Channel. Anglesey is the largest island within the Irish Sea, followed by the Isle of Man...

. On 29 January she shelled the airship shed
Airship hangar
Airships are sheltered in airship hangars during construction and sometimes also for regular operation, particularly at bad weather conditions. Rigid airships always needed to be based in airship hangars because weathering was a serious risk.- History :...

s on Walney Island
Walney Island
The Isle of Walney, also known as Walney Island, is an island in the United Kingdom which lies off the west coast of England, at the northern tip of Morecambe Bay. It forms part of the Borough of Barrow-in-Furness, and it is separated from the mainland at Barrow by Walney Channel, a narrow channel...

 off Barrow-in-Furness
Barrow-in-Furness is an industrial town and seaport which forms about half the territory of the wider Borough of Barrow-in-Furness in the county of Cumbria, England. It lies north of Liverpool, northwest of Manchester and southwest from the county town of Carlisle...

, but was driven off by shore batteries.

In the Mediterranean 1915-17

On 5 June 1915, U-21 was transferred to 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...

 to support Germany's ally, Turkey
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...

. During this voyage, she evaded air attack in the Strait of Gibraltar
Strait of Gibraltar
The Strait of Gibraltar is a narrow strait that connects the Atlantic Ocean to the Mediterranean Sea and separates Spain in Europe from Morocco in Africa. The name comes from Gibraltar, which in turn originates from the Arabic Jebel Tariq , albeit the Arab name for the Strait is Bab el-Zakat or...

 and became the first U-boat to enter the Mediterranean and the first submarine to refuel at sea. Arriving off Galipoli on 25 May, she sighted the pre-Dreadnought battleship, 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...

, which was at anchor bombarding Turkish coastal artillery
Coastal artillery
Coastal artillery is the branch of armed forces concerned with operating anti-ship artillery or fixed gun batteries in coastal fortifications....

 at Gaba Tepe. Approaching to within 300 metres, Hersing fired a single torpedo, which penetrated the Triumph's torpedo nets
Torpedo nets
Torpedo nets were a passive naval warship defensive device against torpedoes. Their use was common practice from the 1890s through World War II...

 and then her hull. She began to list and capsized within 10 minutes; 73 of her crew of nearly 600 were lost. Most of the British and French battleships were withdrawn, but two days later, it was felt that it would be safe for 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...

 to resume the bombardment, close inshore and surrounded by transport ships and torpedo nets. U-21 fired two torpedoes through a gap in the barricade and the Majestic quickly sank; 40 of her crew were lost. The U-boat had been spotted by an RNAS aircraft flown by Wing Commander Samson which made several bombing runs. Hersing escaped by diving under the French battleship Henri IV
French battleship Henri IV
Henri IV was a pre-dreadnought battleship of the French Navy built to test some of the ideas of the prominent naval architect Louis-Émile Bertin. She began World War I as guardship at Bizerte. She was sent to reinforce the Allied naval force in the Dardanelles campaign of 1915, although some of her...

; when the U-boat reappeared later, Samson had run out of bombs and could only fire his rifle
The Lee-Enfield bolt-action, magazine-fed, repeating rifle was the main firearm used by the military forces of the British Empire and Commonwealth during the first half of the 20th century...

 at her.

U-21 retired to 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:...

. On 4 July she sank the French transport ship Carthage and then made her way into the Adriatic Sea
Adriatic Sea
The Adriatic Sea is a body of water separating the Italian Peninsula from the Balkan peninsula, and the system of the Apennine Mountains from that of the Dinaric Alps and adjacent ranges...

, where she joined the Deutsche U-Flotilla Pola, based at Cattaro. On the 8th February 1916, U21 sank the French armored cruiser Amiral Charner
French armoured cruiser Amiral Charner
The Amiral Charner was an armoured cruiser of the French Navy, lead ship of her class.In 1896, she was sent to the Mediterranean to operate the station off Crete. From 1901, she operated in the Far East. In 1905, she was put in the reserve in Toulon....

 off the Syria
Syria , officially the Syrian Arab Republic , is a country in Western Asia, bordering Lebanon and the Mediterranean Sea to the West, Turkey to the north, Iraq to the east, Jordan to the south, and Israel to the southwest....

n coast.

End of the War

In March 1917 she joined 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...

 in Kiel
Kiel is the capital and most populous city in the northern German state of Schleswig-Holstein, with a population of 238,049 .Kiel is approximately north of Hamburg. Due to its geographic location in the north of Germany, the southeast of the Jutland peninsula, and the southwestern shore of the...

. The U-21 survived the war and still under Hersing's command, accidentally sank on 22 February 1919 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...

 while under tow by a British warship. Some accounts maintain that she was scuttle
Scuttling is the act of deliberately sinking a ship by allowing water to flow into the hull.This can be achieved in several ways—valves or hatches can be opened to the sea, or holes may be ripped into the hull with brute force or with explosives...

d by Hersing, who took up potato farming after the war. During the war, the U-21 sank a total of 40 Allied ships (113,580 tons) and damaged two further ships (8,918 tons).

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