O 21-class submarine

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.Jalhay (1982), p. 118.von Münching (1978), p. 38. They were similar to the submarines of the {{sclass|O 19|submarine|4}}, except the boats had no minelaying capability.van Willigenburg (2010), p. 68. The omission of the minelaying capability resulted in a smaller and more streamlined hull which made it possible to reach a higher surface speed.Gardiner and Chesneau (1980), p. 392. Visually the boats showed many similarities to the German Type VII submarine.Bosscher and Busssemaker (2007), p. 26. The submarines of the O 21 class had a length of {{convert|77.70|m|ftin}}, a beam of {{convert|6.80|m|ftin}} and a draught of {{convert|3.95|m|ftin}}.Bosscher and Busssemaker (2007), p. 86. Above water they had a displacement of 990 tons and submerged they had displacement of 1,205 tons.Jalhay (1982), p. 127. There was enough space aboard for a crew of 39 to 60 persons.Bosscher and Busssemaker (2007), p. 27.von Münching (1978), pp. 37-38.

One of the requirements the RNN set for the O 21 class was that it had to be able to dive {{convert|20|m|abbr=on}} deeper than the previous class, which was the O 19 class.Gerretse and Wijn (1993), p. 9.

The primary armament of the O 21-class submarines consisted of eight {{convert|53.3|cm|adj=on}} torpedo tubes; four were located at the bow, two at the stern and two external amidships.Lenton (1968), p. 43. There was room for a total of fourteen torpedoes, with eight being in the torpedo tubes and six for reloads.van Willigenburg (2010), p. 69. Besides the eight torpedo tubes the O 21 class was also equipped with an {{cvt|8.8|cm}} deck gun, two single-mounted {{cvt|40|mm}} anti-aircraft guns and a single {{cvt|12.7|mm}} machine gun. 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.

The O 21-class submarines were equipped with two seven-cylinder two-stroke Sulzer 7 QD 42/50 diesel engines that each could produce {{convert|1000|shp|lk=in}} and drive the two screws of the submarine to a maximum surface speed of {{convert|19.5|kn|lk=in}}.van den Pol (1990), p. 288. Besides the two diesel engines, the submarines also had two electric motors that each could produce {{convert|500|bhp|bhp|lk=in}} and two banks of 96 cells batteries with a capacity of 5,350 Ah.Jalhay (1982), p. 127. This allowed the submarine to operate solely on electric power for five hours. The maximum underwater speed was {{convert|9|kn}}.

File:De 0.23 weer in ons land-519268.ogv

The boats were built by three different shipyards. O 21 and O 22 were built by the Koninklijke Maatschappij De Schelde.Mark (1997), pp. 85-86.

O 23, O 24, O 26 and O 27 by RDM and O 25 at the Wilton-Fijenoord shipyard.

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{{reflist}}

• {{cite book |last1=Bosscher |first1=Ph.M. |last2=Bussemaker |first2=H.O. |date=2007 |title=Gelouterd door strijd: De Nederlandse Onderzeedienst tot de val van Java, 1942 |language=Dutch |edition= |url= |location=Amsterdam |publisher=De Bataafsche Leeuw |page= |isbn=978-90-6707-614-2}}
• {{cite book |editor-last1=Gardiner |editor-first1=Robert |editor-last2=Chesneau |editor-first2=Roger |date=1980 |title= Conway's All the World's Fighting Ships 1922–1946 |location=London |publisher=Conway Maritime Press |isbn=0-85177-146-7}}
• {{cite book|last1=Gerretse|first1=K.H.L.|first2=J.J.A.|last2=Wijn|title=Drie-cylinders duiken dieper: de onderzeeboten van de dolfijn-klasse van de Koninklijke Marine|year=1993|publisher=Van Soeren|location=Amsterdam|isbn=9068810278}}
• {{cite book |last=Jalhay |first=P.C. |date=1982 |title=Nederlandse Onderzeedienst 75 jaar |language=Dutch |edition= |url= |location=Bussum |publisher=De Boer Maritiem |page= |isbn=90-228-1864-0}}
• {{cite book |last=Lenton |first=H.T. |date=1968 |title=Royal Netherlands Navy |location=London |publisher=Macdonald & Co. |series=Navies of the Second World War}}
• {{cite book |last=Mark |first=Chris |date=1997 |title=Schepen van de Koninklijke Marine in W.O. II |language=Dutch|edition= |url= |location=Alkmaar |publisher=De Alk |page= |isbn=90-6013-522-9}}
• {{cite book |editor-last=Raven |editor-first=G.J.A. |date=1988 |title=De kroon op het anker: 175 jaar Koninklijke Marine |language=Dutch|edition= |url= |location=Amsterdam |publisher=De Bataafsche Leeuw |page= |isbn=90-6707-200-1}}
• {{cite magazine |last=van den Pol |first=E. |date=1989 |title=Aspects of submarines - Part I: Some notes on development|magazine=Schip en Werf|location=Rotterdam |publisher=Wyt & Zonen |volume=56|issue=10|issn= 0036-6099|pages=352-358}}
• {{cite magazine |last=van den Pol |first=E. |date=1990 |title=Aspects of submarines - Part IV: The submarine and the diesel engine|magazine=Schip en Werf|location=Rotterdam |publisher=Wyt & Zonen |volume=57|issue=5|issn= 0036-6099|pages=285-293}}
• {{cite book |last=van Willigenburg |first=Henk |date=2010 |title=Dutch Warships of World War II |location=Emmen |publisher=Lanasta |isbn=978-90-8616-318-2}}
• {{cite book |last=von Münching |first=L.L. |date=1978 |title=Schepen van de Koninklijke Marine in de Tweede Wereldoorlog |language=Dutch|edition= |url= |location=Alkmaar |publisher=Alk |page= |isbn=90-6013-903-8}}

• {{cite book|last1=Jalhay|first1=P.C.|last2=Wijn|first2=J.J.A.|title=Ik nader ongezien! De onderzeeboten van de Koninklijke Marine|year=1997|publisher=De Bataafsche Leeuw|location=Amsterdam|isbn=9067074624}}
• {{cite magazine |last=van Herwijnen |first=C. |url=https://www.klaarvooronderwater.nl/kvo/Kvo-064.pdf|date=June 1998|title=De snuiver (deel I)|magazine=Klaar Voor Onderwater |issue=64|location=Den Helder |publisher=Onderzeedienst Reünistenvereniging |pages=8-9 |language=Dutch}}

• [http://www.dutchsubmarines.com/classes/class_o21.htm Description of class]

{{O 21 class submarine}}

{{WWII Dutch ships}}

Category:Submarines of the Netherlands