View source for HMS M21

{{Use dmy dates|date=December 2016}}
{{Use British English|date=December 2016}}
{|{{Infobox ship begin}}
{{Infobox ship image
|Ship image=HMS M21 WWI IWM SP 2030.jpg
|Ship caption=
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{{Infobox ship career
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|Ship country=United Kingdom
|Ship flag={{shipboxflag|United Kingdom|naval}}
|Ship name=HMS ''M21''
|Ship namesake=
|Ship ordered=
|Ship builder=Sir Raylton Dixon & Co.
|Ship laid down=1 March 1915
|Ship launched=27 May 1915
|Ship acquired=
|Ship commissioned=
|Ship decommissioned=
|Ship in service=
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|Ship struck=
|Ship reinstated=
|Ship honours=
|Ship fate=Sunk 20 October 1918 off Dover
|Ship notes=
}}
{{Infobox ship characteristics
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|Header caption= 
|Ship class=[[M15 class monitor|''M15'' class]] [[monitor (warship)|monitor]]
|Ship tonnage=
|Ship displacement=540 tons
|Ship length={{convert|177|ft|3|in|m|abbr=on}}
|Ship beam={{convert|31|ft|m|abbr=on}}
|Ship height=
|Ship draught={{convert|6|ft|9|in|m|abbr=on}}
|Ship depth=
|Ship power=
|Ship propulsion=*2 shaft
*Triple Expansion steam engines
*600 ihp
|Ship sail plan=
|Ship speed=11 [[Knot (unit)|knots]]
|Ship range=
|Ship endurance=
|Ship boats=
|Ship capacity=
|Ship troops=
|Ship complement=69
|Ship crew=
|Ship time to activate=
|Ship sensors=
|Ship EW=
|Ship armament=
*''As built''
*1 × [[BL 9.2 inch gun Mk III - VII|BL 9.2 inch Mk VI gun]]
*1 × [[QF 12 pounder 12 cwt naval gun|12-pdr (76&nbsp;mm) QF Mk 1 gun]]
*1 × [[QF 6 pounder Hotchkiss|6-pdr (57&nbsp;mm) QF MK 1 AA gun]]
*''1918''
*1 × [[BL 7.5 inch Mk II - V naval gun|BL {{convert|7.5|in|mm|adj=on|sigfig=4}} Mk III 50-caliber gun]]
*1 × [[QF 3 inch 20 cwt|QF {{convert|3|in|mm|adj=on|sigfig=4}} AA gun]]
*1 × [[QF 12 pounder 12 cwt naval gun|12-pdr (76&nbsp;mm) QF Mk 1 gun]]
|Ship armour=
|Ship notes=
}}
|}
'''HMS ''M21'' ''' was a [[World War I|First World War]] [[Royal Navy]] [[M15 class monitor|''M15''-class]] [[Monitor (ship)|monitor]]. After service in the [[Mediterranean]] and the [[Dover Patrol]], she struck a mine off [[Ostend]] in January 1918 and sank off [[Dover]].

==Design==
Intended as a shore bombardment vessel, ''M21''{{'}}s primary armament was a single [[BL 9.2 inch gun Mk I - VII|9.2 inch Mk VI gun]] removed from the {{sclass|Edgar|cruiser}} [[HMS Theseus (1892)|HMS ''Theseus'']].<ref>{{cite book | title = Conway's All the World's Fighting Ships 1906-1921 | editor = Randal Gray | year = 1985 | isbn = 0-85177-245-5 | publisher= Conway Maritime Press | page = 48}}</ref> In addition to her 9.2 inch gun, she also possessed one [[QF 12 pounder 12 cwt naval gun|12 pounder]] and one [[QF 6 pounder Hotchkiss|six pound anti-aircraft gun]]. Due to the shortage of Bolinder diesel engines that equipped her sisters, she was fitted with 2 shaft triple expansion steam engines that allowed a top speed of eleven knots. The monitor's crew consisted of sixty nine officers and men.

==Construction==
HMS ''M21'' ordered in March, 1915, as part of the [[War Emergency Programme destroyers|War Emergency Programme]] of ship construction. She was laid down at the [[Sir Raylton Dixon|Sir Raylton Dixon & Co.]] Ltd shipyard at [[Govan]] in March 1915, launched on 27 May 1915, and completed in July 1915.

==World War I==
''M21'' served initially in the [[Mediterranean]] from September 1915. On her return from the Mediterranean in September 1917, ''M21'' had her main 9.2&nbsp;in gun removed, as it was required for artillery use on the [[Western Front (World War I)|Western Front]], and a [[BL 7.5 inch Mk II - V naval gun|BL {{convert|7.5|in|mm|adj=on|sigfig=4}} Mk III 50-caliber gun]] was fitted in lieu.

''M21'' then served with the [[Dover Patrol]] from October 1917.

==Loss==
''M21'' struck a mine off Ostend on 20 October 1918.  She was taken in tow to Dover, but sank off West Pier.

==Citations==
{{Reflist}}

==References==
*{{Cite Colledge2006}}
*Dittmar, F. J. & Colledge, J. J., "British Warships 1914-1919", (Ian Allan, London, 1972), {{ISBN|0-7110-0380-7}}

{{M15 class monitors}}
{{October 1918 shipwrecks}}
{{clear}}

{{coord missing|English Channel}}

{{DEFAULTSORT:M21}}
[[Category:M15-class monitors]]
[[Category:1915 ships]]
[[Category:World War I monitors of the United Kingdom]]
[[Category:Ships sunk by mines]]
[[Category:Maritime incidents in 1918]]
[[Category:World War I shipwrecks in the English Channel]]
[[Category:Royal Navy ship names]]