German submarine U-21 (1936)

German submarine U-21 was a Type IIB U-boat of Nazi Germany's Kriegsmarine. Her keel was laid down 4 March 1936, by Germaniawerft of Kiel as yard number 551. She was commissioned on 3 August 1936. During World War II, she conducted operations against enemy shipping.

U-21 went on seven war patrols, sinking five merchant ships and damaging one warship.

Design
German Type IIB submarines were enlarged versions of the original Type IIs. U-21 had a displacement of 279 t when at the surface and 328 t while submerged. Officially, the standard tonnage was 250 LT, however. The U-boat had a total length of 42.70 m, a pressure hull length of 28.20 m, a beam of 4.08 m, a height of 8.60 m, and a draught of 3.90 m. The submarine was powered by two MWM RS 127 S four-stroke, six-cylinder diesel engines of 700 PS for cruising, two Siemens-Schuckert PG VV 322/36 double-acting electric motors producing a total of 460 PS for use while submerged. She had two shafts and two 0.85 m propellers. The boat was capable of operating at depths of up to 80 - 150 m.

The submarine had a maximum surface speed of 12 kn and a maximum submerged speed of 7 kn. When submerged, the boat could operate for 35 - 42 nmi at 4 kn; when surfaced, she could travel 3800 nmi at 8 kn. U-21 was fitted with three 53.3 cm torpedo tubes at the bow, five torpedoes or up to twelve Type A torpedo mines, and a 2 cm anti-aircraft gun. The boat had a complement of twentyfive.

First, second and third patrols
U-21's first patrol was relatively uneventful.

On her second foray, the boat was attacked by the British submarine HMS Ursula (N59) which fired six torpedoes at her in the North Sea northeast of Berwick-Upon-Tweed [On the English/Scottish border] on 17 September 1939. These were the first submarine weapons launched by the Royal Navy in the Second World War. They all missed.

On her third patrol, the U-boat also had torpedoes fired at her in the central North Sea by another British submarine, HMS Sealion (72S). The result was inconclusive as well.

Fourth and fifth patrols
The boat's first success with a torpedo came on 1 December 1939 when she sank the Finnish-registered Mercator about 12 nmi southeast of Buchan Ness (near Peterhead). She also damaged the British cruiser HMS Belfast (C35) with a mine.

On her fifth sortie, she sank Mars on 21 December 1939 and Carl Henckel (both from Sweden).

Sixth patrol
Patrol number six saw her sink the Danish Vidar 100 nmi east of the Moray Firth on 31 January 1940.

Seventh patrol
She sank the British Royal Archer with a mine on 26 February 1940, but then it all went horribly wrong on 27 March when she ran aground off Oldknuppen Island after a navigational error. The boat was towed to Mandal in Norway where she was interned. She was then towed to Kristiansand for repairs and released on 9 April after the German occupation of the Nordic country.

Fate
In July she was transferred to the 21st U-boat Flotilla in Kiel as a training boat, with whom she remained for the rest of the war. U-21 was scrapped in February 1945.