Part of the O 21class, consisting of the O21-27, preceded by the O19 class. The O23 was first to be named K XXIII indicating that she was to serve in the Dutch East Indies. Laid down by Rotterdamsche Droogdokdok Maatschappij, Rotterdam, Netherlands on 12 October 1937, launched on 5 December 1939, commissioned on 13 May 1940, escaped to Portsmouth, England, completed by the John Thornycroft shipyard, decommissioned on 1 December 1948 and sold to be broken up in April 1949.
Displacement 990 (surfaced)-1.205 (submerged) tons and as dimensions 77,7 x 6,8 x 3,95 metres or 254.11 x 22,4 x 13,0 feet. The machinery consisted of 2x2.500 bhp diesels and 2x500bhp electric motors allowing a speed of 19,5 (surfaced)-9 (submerged) knots. Range 10.000 (surfaced, speed 12knots)-28 (submerged 8,5) nautical miles. Crew numbered 39 men, Armament consisted of 8-53,3cm/21” torpedo tubes (4-bow, 2 stern, 1x2external-traversssing amidships), 1-8,8cm gun, 2x1-cm machineguns and 1-12,7mm/0.,50“ machine gun . Sunk in the Second World War an Italians tanker and sunk or damaged 4 Japanese ships.
