HNLMS O 23

O 23
History
Netherlands
Name	O 23
Builder	Rotterdamsche Droogdok Maatschappij , Rotterdam
Yard number	RDM-205 [1]
Laid down	12 October 1937
Launched	5 December 1939
Commissioned	13 May 1940
Decommissioned	1 December 1948
Fate	Sold for scrap, April 1949
General characteristics
Class & type	O 21-class submarine
Displacement	987 long tons (1,003  t) (surfaced) 1,488 long tons (1,512 t) (submerged)
Length	255 ft (77.7 m)
Beam	21 ft 6 in (6.6 m)
Draft	13 ft (4.0 m)}
Propulsion	2 × 2,500  bhp (1,864  kW) diesel engines 2 × 500 bhp (373 kW) electric motors
Speed	19.5 knots (36.1 km/h; 22.4 mph) (surfaced) 9 kn (17 km/h; 10 mph) (submerged)
Range	10,000  nmi (19,000 km; 12,000 mi) at 11 knots (20 km/h; 13 mph) (surfaced) 28 nmi (52 km; 32 mi) at 9 kn (17 km/h; 10 mph) (submerged)
Test depth	330 ft (100 m)
Complement	60
Armament	4 × 21 in (533 mm) bow torpedo tubes 2 × 21 in (533 mm) stern torpedo tubes 2 × 21 in (533 mm) external traversing torpedo tubes 2 × single 40 mm (1.6 in) AA guns

O 22 was a O 21-class submarine built for the Royal Netherlands Navy during the 1930s for European service. Completed in 1940, she sank several ships during World War II in the Mediterranean and in the Indian Ocean.

Design and description

The O 21-class submarines were slightly smaller versions of the preceding O 19 class since they lacked that class's minelaying capability. The boats had a length of 255 feet (77.7 m) overall, a beam of 21 feet 6 inches (6.6 m) and a draft of 13 feet (4.0 m). ^[2] They displaced 987 long tons (1,003 t) on the surface and 1,488 long tons (1,512 t) submerged. The submarines had a crew of 60 officers and enlisted men. ^[3]

For surface running, the boats were powered by two 2,500- brake-horsepower (1,864 kW) Sulzer diesel engines, each driving one propeller shaft. When submerged each propeller was driven by a 500-horsepower (373 kW) electric motor. They could reach 19.5 knots (36.1 km/h; 22.4 mph) on the surface and 9 knots (17 km/h; 10 mph) underwater. On the surface, the boats had a range of 10,000 nautical miles (19,000 km; 12,000 mi) at 12 knots (22 km/h; 14 mph) and 28 nmi (52 km; 32 mi) at 9 knots submerged. The submarines had a diving depth of 330 feet (100 m). ^[2]

The O 21 class was armed with eight 21-inch (533 mm) 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 40-millimeter (1.6 in) Bofors AA guns; ^[3] these were on single watertight mounts that retracted into the conning tower when submerged. ^[4]

Construction and career

O 23 in the Bay of Gibraltar in 1941

O 23 was ordered on 19 June 1937 and laid down on 12 October 1937 at the shipyard of Rotterdamsche Droogdok Maatschappij in Rotterdam. The boat was launched on 5 December 1939. Following the German invasion of 10 May 1940, O 23 was hastily commissioned, still incomplete, and sailed for England on 13 May, together with her sister O 24, to be completed at the Thornycroft shipyard at Southampton. ^[5]

During the war she operated in the North Sea, the Mediterranean Sea and the Indian Ocean. O 23 made twenty patrols during the war in the course of which she sank or damaged five ships. She survived the war and was decommissioned on 1 December 1948, being sold for scrap in April of the following year. ^[5]

Summary of raiding history

Ships sunk and damaged by O 23. ^[5]

Date	Ship name	Nationality/Type	Tonnage (GRT)	Fate
30 June 1941	Capacitas	Italian tanker	5371	Sunk
27 July 1942	Shofuku Maru No.2	Japanese merchant ship	729	Damaged
2 August 1942	Zenyo Maru	Japanese army cargo ship	6440	Damaged (burned out and later declared a total loss)
2 August 1942	Ohio Maru	Japanese transport ship	5872	Sunk
25 October 1942	Shinyu Maru	Japanese merchant ship	4622	Damaged

References

1. "Bouwnummer RDM-205, Hr. Ms. "O 23", 1940, onderzeeboot". RDM-archief (in Dutch).
2. Bagnasco, p. 240
3. van Willigenburg, p. 69
4. Bagnasco, p. 238
5. Helgason, Guðmundur (2013). "HNMS O 23". uboat.net. Retrieved 24 June 2025.

Bibliography

• Bagnasco, Erminio (2018) [1977]. Submarines of World War Two: Design, Development and Operations. Naval Institute Press. ISBN   978-1-68247-384-9.
• Lenton, H.T. (1968). Royal Netherlands Navy. Navies of the Second World War. Macdonald & Co.
• Mark, Chris (1997). Schepen van de Koninklijke Marine in W.O. II (in Dutch). Alkmaar: De Alk. ISBN   90-6013-522-9.
• Noppen, Ryan K. (2020). The Royal Netherlands Navy of World War II. New Vanguard. Vol. 285. Osprey Publishing. ISBN   978-1-4728-4191-9.
• van Willigenburg, Henk (2010). Dutch Warships of World War II. Lanasta. ISBN   978-90-8616-318-2.

Further reading

• Drijfhout van Hooff, J.F. (December 1992). "De Meidagen van 1940" (PDF). Klaar Voor Onderwater (in Dutch). No. 41. Den Helder: Onderzeedienst Reünistenvereniging. pp. 4–12.
• Drijfhout van Hooff, J.F. (March 1993). "De Meidagen van 1940 (II)" (PDF). Klaar Voor Onderwater (in Dutch). No. 42. Den Helder: Onderzeedienst Reünistenvereniging. pp. 3–9.