|Ordered||2 Feb 1935|
|Laid down||4 Mar 1936||F. Krupp Germaniawerft AG, Kiel (werk 551)|
|Launched||31 Jul 1936|
|Commissioned||3 Aug 1936|
|Successes||5 ships sunk, total tonnage 10,706 GRT|
1 auxiliary warship sunk, total tonnage 605 GRT
1 warship damaged, total tonnage 11,500 tons
Decommissioned on 5 August 1944 at Pillau and cannibalized for spare parts. The hulk was captured by Soviet forces in Pillau on 25 April 1945 and probably broken up.
Ran aground at 2330hrs on 26 March 1940 on Oddknuppen Island, south-east of Mandal, Norway, in position 57.57,5N, 07.34,5E, due to a navigational error. On 28 March 1940 refloated and interned by Norway, first at Mandal and later at Kristiansand-Marviken. Recaptured by Germany on 9 April 1940 and returned to service after being repaired in Kiel.
Attacks on this boat and other events
9 Sep 1939
HMS Ursula (N 59) (Lt.Cdr. G.C. Philips, RN) fired the first British submarine torpedoes of the war in unsuccessfully attacking U-35 and U-21 with a spread of five torpedoes some 23 miles (37 km) north of the Dutch island of Schiermonnikoog. (Sources: Dr. Jürgen Rohwer)
6 Nov 1939
HMS Sealion (Lt.Cdr. B. Bryant, RN) fired six torpedoes at U-21, all of which missed their target.
2 recorded attacks on this boat.
Men lost from U-boats
Unlike many other U-boats, which during their service lost men due to accidents and various other causes, U-21 did not suffer any casualties (we know of) until the time of her loss.
There was another U-21 in World War One
That boat was launched from its shipyard on 8 Feb 1913 and commissioned into the Imperial Navy on 22 Oct 1913. The Naval war in WWI was brought to an end with the Armistice signed on 11 Nov, 1918. Read about SM U 21 during WWI.