O 21-class submarine

O 21
Class overview
Name	O 21 class
Builders	Rotterdamsche Droogdok Maatschappij Koninklijke Maatschappij De Schelde Wilton-Fijenoord
Operators	Royal Netherlands Navy   Kriegsmarine
Preceded by	O 19 class
Succeeded by	Dolfijn class
Built	1937–1942 [1]
In commission	1940–1959 [2]
Completed	7
Lost	2
Scrapped	5
General characteristics [3]
Type	Submarine
Displacement	990 tons surfaced 1205 tons submerged
Length	77.7 m (254 ft 11 in)
Beam	6.8 m (22 ft 4 in)
Draught	3.95 m (13 ft 0 in)
Propulsion	2 shafts 2 × Sulzer 7 QD 42/50 diesel engines, 2,500 bhp (1,864 kW) each 2 × 500 bhp (373 kW) electric motors 2 × 96 cells batteries (5350 Ah)
Speed	19.5  kn (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 12 kn (22 km/h; 14 mph) surfaced 28  nmi (52 km; 32 mi) at 8.5 kn (15.7 km/h; 9.8 mph) submerged
Complement	39
Armament	8 × 21 in (530 mm) torpedo tubes (4 bow, 2 stern, 2 traversing amidships ) 1 × 88 mm deck gun 2 × 40 mm AA guns 1 × 12.7 mm machine gun

The O 21 class was a class of seven submarines, built for the Royal Netherlands Navy. ^[2] The boats were still incomplete at the start of the German invasion of the Netherlands, O 21, O 22, O 23 and O 24 were hastily launched and escaped to the United Kingdom. O 25, O 26 and O 27 were not able to escape and were captured by the German forces. The Kriegsmarine ordered the completion of the boats and they entered German service as UD-3, UD-4 and UD-5. The submarines' diving depth was 100 meters (330 ft).

At the start of the Second World War the O 21 class was together with the British U, S and T classes and German Type VII one of the most advanced submarine classes in service at the time. ^[4]

Design

The O 21 class submarines were designed by the Dutch engineer G. de Rooy, chief engineer of the Royal Netherlands Navy (RNN) at the time. ^{[5] [6]} They were similar to the submarines of the O 19 class, except the boats had no minelaying capability. ^[7] The omission of the minelaying capability resulted in a smaller and more streamlined hull which made it possible to reach a higher surface speed. ^[8] Visually the boats showed many similarities to the German Type VII submarine. ^[9] The submarines of the O 21 class had a length of 77.70 metres (254 ft 11 in), a beam of 6.80 metres (22 ft 4 in) and a draught of 3.95 metres (13 ft 0 in). ^[10] Above water they had a displacement of 990 tons and submerged they had displacement of 1,205 tons. ^[11] There was enough space aboard for a crew of 39 to 60 persons. ^{[12] [13]}

One of the requirements the RNN set for the O 21 class was that it had to be able to dive 20 m (66 ft) deeper than the previous class, which was the O 19 class. ^[14]

Armament

The primary armament of the O 21-class submarines consisted of eight 53.3-centimetre (21.0 in) torpedo tubes; four were located at the bow, two at the stern and two external amidships. ^[15] There was room for a total of fourteen torpedoes, with eight being in the torpedo tubes and six for reloads. ^[16] Besides the eight torpedo tubes the O 21 class was also equipped with an 8.8 cm (3.5 in) deck gun, two single-mounted 40 mm (1.6 in) anti-aircraft guns and a single 12.7 mm (0.50 in) machine gun. ^[8] The three unfinished boats (O 25, O 26 and O 27) that were captured and later completed by Nazi Germany during the Second World War had besides the eight torpedo tubes, a single 8.8 cm deck gun, and two 20 mm guns. ^[6]

Propulsion

The O 21-class submarines were equipped with two seven-cylinder two-stroke Sulzer 7 QD 42/50 diesel engines that each could produce 1,000 shaft horsepower (750 kW) and drive the two screws of the submarine to a maximum surface speed of 19.5 knots (36.1 km/h; 22.4 mph). ^{[17] [8]} Besides the two diesel engines, the submarines also had two electric motors that each could produce 500 brake horsepower (500 bhp) and two banks of 96 cells batteries with a capacity of 5,350 Ah. ^[11] This allowed the submarine to operate solely on electric power for five hours. ^[3] The maximum underwater speed was 9 knots (17 km/h; 10 mph). ^[13]

Boats

O 23 returning from patrol in 1946. Dutch newsreel.

The boats were built by three different shipyards. O 21 and O 22 were built by the Koninklijke Maatschappij De Schelde. ^[18] O 23, O 24, O 26 and O 27 by RDM and O 25 at the Wilton-Fijenoord shipyard. ^[2]

O 21 class construction data ^[1]

Name	Laid down	Launched	Commissioned	Decommissioned
O 21	13 July 1937	21 October 1939	10 May 1940 (uncompleted)	2 November 1957
O 22	15 September 1938	20 January 1940	10 May 1940 (uncompleted)	8 November 1940
O 23	12 October 1937	5 December 1939	13 May 1940 (uncompleted)	1 December 1948
O 24	12 November 1937	18 March 1940	13 May 1940 (uncompleted)	22 February 1954
O 25 Commissioned as: UD-3	10 April 1939	1 May 1940	1 March 1942	13 October 1944 3 May 1945 (scuttled)
O 26 Commissioned as: UD-4	20 April 1939	23 November 1940	1 March 1941	3 May 1945 (scuttled)
O 27 Commissioned as: UD-5	3 August 1939	26 September 1941	1 November 1941 13 July 1945 (Dutch navy)	14 November 1959

Notes

Citations

1. Jalhay (1982), pp. 118-120.
2. Raven (1988), p. 178.
3. Bosscher and Busssemaker (2007), pp. 86-87.
4. van den Pol (1989), p. 352.
5. Jalhay (1982), p. 118.
6. von Münching (1978), p. 38.
7. van Willigenburg (2010), p. 68.
8. Gardiner and Chesneau (1980), p. 392.
9. Bosscher and Busssemaker (2007), p. 26.
10. Bosscher and Busssemaker (2007), p. 86.
11. Jalhay (1982), p. 127.
12. Bosscher and Busssemaker (2007), p. 27.
13. von Münching (1978), pp. 37-38.
14. Gerretse and Wijn (1993), p. 9.
15. Lenton (1968), p. 43.
16. van Willigenburg (2010), p. 69.
17. van den Pol (1990), p. 288.
18. Mark (1997), pp. 85-86.

References

• Bosscher, Ph.M.; Bussemaker, H.O. (2007). Gelouterd door strijd: De Nederlandse Onderzeedienst tot de val van Java, 1942 (in Dutch). Amsterdam: De Bataafsche Leeuw. ISBN   978-90-6707-614-2.
• Gardiner, Robert; Chesneau, Roger, eds. (1980). Conway's All the World's Fighting Ships 1922–1946. London: Conway Maritime Press. ISBN   0-85177-146-7.
• Gerretse, K.H.L.; Wijn, J.J.A. (1993). Drie-cylinders duiken dieper: de onderzeeboten van de dolfijn-klasse van de Koninklijke Marine. Amsterdam: Van Soeren. ISBN   9068810278.
• Jalhay, P.C. (1982). Nederlandse Onderzeedienst 75 jaar (in Dutch). Bussum: De Boer Maritiem. ISBN   90-228-1864-0.
• Lenton, H.T. (1968). Royal Netherlands Navy. Navies of the Second World War. London: Macdonald & Co.
• Mark, Chris (1997). Schepen van de Koninklijke Marine in W.O. II (in Dutch). Alkmaar: De Alk. ISBN   90-6013-522-9.
• Raven, G.J.A., ed. (1988). De kroon op het anker: 175 jaar Koninklijke Marine (in Dutch). Amsterdam: De Bataafsche Leeuw. ISBN   90-6707-200-1.
• van den Pol, E. (1989). "Aspects of submarines - Part I: Some notes on development". Schip en Werf. Vol. 56, no. 10. Rotterdam: Wyt & Zonen. pp. 352–358. ISSN   0036-6099.
• van den Pol, E. (1990). "Aspects of submarines - Part IV: The submarine and the diesel engine". Schip en Werf. Vol. 57, no. 5. Rotterdam: Wyt & Zonen. pp. 285–293. ISSN   0036-6099.
• van Willigenburg, Henk (2010). Dutch Warships of World War II. Emmen: Lanasta. ISBN   978-90-8616-318-2.
• von Münching, L.L. (1978). Schepen van de Koninklijke Marine in de Tweede Wereldoorlog (in Dutch). Alkmaar: Alk. ISBN   90-6013-903-8.

Further reading

• Jalhay, P.C.; Wijn, J.J.A. (1997). Ik nader ongezien! De onderzeeboten van de Koninklijke Marine. Amsterdam: De Bataafsche Leeuw. ISBN   9067074624.
• van Herwijnen, C. (June 1998). "De snuiver (deel I)" (PDF). Klaar Voor Onderwater (in Dutch). No. 64. Den Helder: Onderzeedienst Reünistenvereniging. pp. 8–9.

External links

• Description of class