O 21-class submarine

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O 21
Class overview
NameO 21 class
Builders
Operators
Preceded by O 19 class
Succeeded by Dolfijn class
Built1937–1942 [1]
In commission1940–1959 [2]
Completed7
Lost2
Scrapped5
General characteristics [3]
Type Submarine
Displacement
  • 990 tons surfaced
  • 1205 tons submerged
Length77.7 m (254 ft 11 in)
Beam6.8 m (22 ft 4 in)
Draught3.95 m (13 ft 0 in)
Propulsion
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
Complement39
Armament

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).

Contents

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]
NameLaid downLaunchedCommissionedDecommissioned
O 21 13 July 193721 October 193910 May 1940 (uncompleted)2 November 1957
O 22 15 September 193820 January 194010 May 1940 (uncompleted)8 November 1940
O 23 12 October 19375 December 193913 May 1940 (uncompleted)1 December 1948
O 24 12 November 193718 March 194013 May 1940 (uncompleted)22 February 1954
O 25
Commissioned as:
UD-3		10 April 19391 May 19401 March 194213 October 1944
3 May 1945 (scuttled)
O 26
Commissioned as:
UD-4		20 April 193923 November 19401 March 19413 May 1945 (scuttled)
O 27
Commissioned as:
UD-5		3 August 193926 September 19411 November 1941
13 July 1945 (Dutch navy)		14 November 1959

Notes

    Citations

    1. 1 2 Jalhay (1982), pp. 118-120.
    2. 1 2 3 Raven (1988), p. 178.
    3. 1 2 Bosscher and Busssemaker (2007), pp. 86-87.
    4. ↑ van den Pol (1989), p. 352.
    5. ↑ Jalhay (1982), p. 118.
    6. 1 2 von Münching (1978), p. 38.
    7. ↑ van Willigenburg (2010), p. 68.
    8. 1 2 3 Gardiner and Chesneau (1980), p. 392.
    9. ↑ Bosscher and Busssemaker (2007), p. 26.
    10. ↑ Bosscher and Busssemaker (2007), p. 86.
    11. 1 2 Jalhay (1982), p. 127.
    12. ↑ Bosscher and Busssemaker (2007), p. 27.
    13. 1 2 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.

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