SM UB-21 was a German 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

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...

 or 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...

 in the German Imperial Navy  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...

. The U-boat was ordered on 30 April 1915 and launched on 26 September 1915. She was commissioned into the German Imperial Navy on 18 February 1916 as SM UB-21."SM" stands for "Seiner Majestät" (His Majesty's) and combined with the U for Unterseeboot would be translated as His Majesty's Submarine. The submarine sank 33 ships in 26 patrols. UB-21 surrendered, 24 November 1918. UB-21 sank off the English east coast while on way to ship breaker

Ship Breaker

Ship Breaker is a 2010 young adult novel by Paolo Bacigalupi set in a postapocalyptic future. It was a finalist for the 2010 National Book Award for Young People's Literature and won the 2011 Michael L. Printz Award and the Locus Award for Best Young Adult Book...

in 1920.

History
SM UB-21 was a German Type UB II submarine or U-boat in the German Imperial Navy (German: Kaiserliche Marine) 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 18 February 1916 as SM UB-21.The submarine sank 33 ships in 26 patrols.Franz Walther took command on 27 November 1916 to August 1917, completing 2 patols from Germany, then transferred to Fanders Fotilla to undertake 7 patrols to the East Coast of England around the Whitby & Scarborough area. On July 18, 1917 Walther landed an enlisted man sent to blow up railway bridge and a tunnel, he became lost and was later captured. On the 19th July 1918, under the command of Mahn, UB-21 landed 2 men near Whitby to carry out sabotage to an industrial railway and a munitions factor; Interned in Spain, 30/07/1917; Used for training from 1918 to the end of the war.UB-21 surrendered to England on 24/11/1918.To avoid the humiliation of the surrender the Germans had originally planned to scuttle all their U-boats, but this was vetoed when the Allies warned that if Germany failed to surrender her U-boats intact the Allies would permanently occupy the Island base of Heligoland. Such was the ignominious end of an elite which had almost wrested Britain’s century-old undisputed command of the sea from her.U-boats divided among the Allies, one of the French allocation off 46 of which 10 retain for service, all rest, including UB-21 were sold for scrap.On 1/1/1920 Whilst under tow to Cherbourg to be scrapped, the tow line parted and UB-21 collided with the wreck of a steamer that was aground on the Seven Sisters. After some salvage in situ the hull was refloated and taken under tow to be scrapped. Once again she broke her tow and this time foundered in the Solent. The remains of UB-21 lay they until 1921 when the wreck was dispersed using explosives because it was seen to be a navigation hazard. In the early 1970s the wreck was sold to new owners and dived on until finally disappearing in the mud and silt of the Solent.She now lies buried in the silt 2 meter proud.There are armor plates scattered around the wreck.