U-21 may refer to one of the following German submarines:
Germany, officially the Federal Republic of Germany, is a country in Central and Western Europe, lying between the Baltic and North Seas to the north, and the Alps to the south. It borders Denmark to the north, Poland and the Czech Republic to the east, Austria and Switzerland to the south, France to the southwest, and Luxembourg, Belgium and the Netherlands to the west.
- SM U-21 (Germany), was a Type U 19 submarine launched in 1913 and that served in the First World War; sank HMS Pathfinder, the first ship sunk by a torpedo fired from a submarine; U-21 sank on 22 February 1919 while en route to be surrendered
- During the First World War, Germany also had these submarines with similar names:
- SM UB-21, a Type UB II submarine launched in 1915 and surrendered 24 November 1918
- SM UC-21, a Type UC II submarine launched in 1916 and lost in September 1917
Type UC II minelaying submarines were used by the Imperial German Navy during World War I. They displaced 417 tons, carried guns, 7 torpedoes and up to 18 mines. The ships were double-hulled with improved range and seakeeping compared to the UC I type.
SM UB-21 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 26 September 1915. She was commissioned into the German Imperial Navy on 20 February 1916 as SM UB-21. The submarine sank 33 ships in 26 patrols for a total of 36,764 gross register tons (GRT). Surrendered to Britain in accordance with the requirements of the Armistice with Germany, UB-21 sank in 1920 in the eastern Solent while en route to be broken up.
The UB II type submarine was a class of U-boat built during World War I by the German Imperial Navy. 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. In 1915 and 1916, 30 were built at two different shipyards.
SM UC-21 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 1 April 1916. She was commissioned into the German Imperial Navy on 12 September 1916 as SM UC-21.
- During the First World War, Germany also had these submarines with similar names:
- German submarine U-21 (1936), a Type IIB submarine that served in the Second World War; stricken on 5 August 1944 and scrapped in February 1945
- German submarine U-21 (S170), a Type 206 submarine of the Bundesmarine that was launched in 1974 and scrapped in 1998
SM U-21 was a U-boat built for the Imperial German Navy shortly before World War I. The third of four Type U-19-class submarines, these were the first U-boats in German service to be equipped with diesel engines. U-21 was built between 1910 and October 1913 at the Kaiserliche Werft in Danzig. She was armed with four torpedo tubes and a single deck gun; a second gun was added during her career.
World War I, also known as the First World War or the Great War, was a global war originating in Europe that lasted from 28 July 1914 to 11 November 1918. Contemporaneously described as "the war to end all wars", it led to the mobilisation of more than 70 million military personnel, including 60 million Europeans, making it one of the largest wars in history. It is also one of the deadliest conflicts in history, with an estimated nine million combatants and seven million civilian deaths as a direct result of the war, while resulting genocides and the 1918 influenza pandemic caused another 50 to 100 million deaths worldwide.
HMS Pathfinder was the lead ship of the Pathfinder class of scout cruisers, and was the first ship ever to be sunk by a locomotive torpedo fired by submarine. She was built by Cammell Laird, Birkenhead, launched on 16 July 1904, and commissioned on 18 July 1905. She was originally to have been named HMS Fastnet, but was renamed prior to construction.
U-21 or U-XXI may also refer to:
- SM U-21 (Austria-Hungary), a U-20-class submarine of the Austro-Hungarian Navy
SM U-21 or U-XXI was a U-20-class submarine or U-boat built for and operated by the Austro-Hungarian Navy during the First World War. The design for U-21 was based on submarines of the Royal Danish Navy's Havmanden class, and was largely obsolete by the beginning of the war.
The U-20 class was a class of four submarines or U-boats built for and operated by the Austro-Hungarian Navy during World War I. The class is sometimes referred to as the Havmanden class because it was based upon the design of the Royal Danish Navy's 1911 Havmanden-class submarines, three of which were built in Fiume.
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