HNLMS O 21
Design and description
The O 21-class submarines were slightly smaller versions of the preceding since they lacked that class's minelaying capability. The boats had a length of overall, a beam of and a draft of. They displaced on the surface and submerged. The submarines had a crew of 60 officers and enlisted men.For surface running, the boats were powered by two Sulzer diesel engines, each driving one propeller shaft. When submerged each propeller was driven by a electric motor. They could reach on the surface and underwater. On the surface, the boats had a range of at and at 9 knots submerged. The submarines had a diving depth of.
The O 21 class was armed with eight torpedo tubes. Four of these were in the bow and two tubes were in the stern. The other pair were on an external rotating mount amidships. A reload was provided for each internal torpedo tube. They were also armed with two Bofors AA guns; these were on single watertight mounts that retracted into the conning tower when submerged.
Construction and career
O 21 was ordered on 19 June 1937 and laid down on 20 November 1937 at the shipyard of Koninklijke Maatschappij De Schelde in Vlissingen. The boat was launched on 21 October 1939. Following the German invasion of 10 May 1940, O 21 was hastily commissioned that afternoon, still incomplete, and sailed for England together with her sister and the tugboat B.V. 37, to be finally completed at Rosyth Dockyard.During the war she operated around England, the Mediterranean Sea, in the Indian Ocean and Fremantle off the west coast of Australia. O 21 sank U-95 in the western Mediterranean on 28 November 1941. She survived the war and was decommissioned on 2 November 1957 and sold for scrap the following year to the firm v. Beekum in Alkmaar.