View source for 20 mm/70 Oerlikon Mk.II (20 mm)

[[File:20 mm 70 Oerlikon Mk.II (20 mm).jpg|thumb|x250px|One of the two 20 mm/70 Oerlikon Mk.II on the stern of [[HMAS Nepal]]]]
== Description ==
<!-- ''Write an introduction to the article in 2-3 small paragraphs. Briefly tell us about the history of the development and combat using the weaponry and also about its features. Compile a list of air, ground, or naval vehicles that feature this weapon system in the game.'' -->
The '''20 mm/70 Oerlikon Mk.II''' is a rapid-firing anti-aircraft cannon that played a crucial role in World War II and beyond. Developed by the Swiss company Oerlikon in the 1930s, this weapon system quickly gained popularity due to its high rate of fire, reliability, and versatility. It was widely used by the Allied forces during World War II and continued to serve in many navies around the world well into the 21st century.

=== Vehicles equipped with this weapon ===
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{{Navigation-Start|Vehicles equipped with this weapon}}

{{Navigation-First-Line|'''SPAA'''}}{{Specs-Link|uk_armored_car_mk_2_aa}}{{-}}{{Specs-Link|uk_crusader_aa_mk_2}}

{{Navigation-First-Line|'''Motor torpedo boats'''}}{{Specs-Link|us_elco_80ft_pt_boat}}{{-}}{{Specs-Link|us_elco_80ft_pt109_boat}}{{-}}{{Specs-Link|us_elco_80ft_pt174}}{{-}}{{Specs-Link|us_elco_80ft_pt_boat_mod01}}{{-}}{{Specs-Link|us_elco_80ft_pt_boat_thunderbolt}}{{-}}{{Specs-Link|us_elco_80ft_pt_boat_mod02}}{{-}}{{Specs-Link|us_higgins_78ft_pt71}}{{-}}{{Specs-Link|us_higgins_78ft_pt625}}{{-}}{{Specs-Link|us_higgins_78ft_pt658}}
{{Navigation-Line| }}{{Specs-Link|uk_mtb_vosper_2series}}{{-}}{{Specs-Link|uk_higgins_78ft_mtb422}}{{-}}{{Specs-Link|fr_mtb96_vosper}}{{-}}{{Specs-Link|fr_mtb96_vosper}}{{-}}{{Specs-Link|fr_vlt2}}{{-}}{{Specs-Link|fr_type40k_vedette}}

{{Navigation-Line|'''Motor gun boats'''}}{{Specs-Link|us_pgm_59_class}}{{-}}{{Specs-Link|us_lcs_l_3}}{{-}}{{Specs-Link|us_nasty_ptf}}{{-}}{{Specs-Link|us_admirable_class}}
{{Navigation-Line| }}{{Specs-Link|uk_fairmile_b_ml345}}{{-}}{{Specs-Link|uk_fairmile_c_332}}{{-}}{{Specs-Link|uk_hdml_ml1383}}{{-}}{{Specs-Link|uk_sgb_304}}{{-}}{{Specs-Link|uk_sgb_309}}
{{Navigation-Line| }}{{Specs-Link|jp_yuri_class_asagao}}{{-}}{{Specs-Link|it_alano_9851}}

{{Navigation-Line|'''Armoured gun boats'''}}{{Specs-Link|us_lcm_zippo}}

{{Navigation-Line|'''Gunboats'''}}{{Specs-Link|uk_frigate_river}}{{-}}{{Specs-Link|fr_frigate_croix_de_lorraine_class_la_surprise}}

{{Navigation-Line|'''Sub-chasers'''}}{{Specs-Link|us_sc_497}}{{-}}{{Specs-Link|us_pc_451}}{{-}}{{Specs-Link|us_pc_466_carmi}}

{{Navigation-Line| }}{{Specs-Link|uk_flower_class}}{{-}}{{Specs-Link|uk_isles_class_trawler}}

{{Navigation-Line|'''Frigates'''}}{{Specs-Link|us_frigate_tacoma}}{{-}}{{Specs-Link|us_frigate_buckley_class_coolbaugh}}

{{Navigation-First-Line|'''Destroyers'''}}{{Specs-Link|us_destroyer_clemson_barker}}{{-}}{{Specs-Link|us_destroyer_farragut_1942}}{{-}}{{Specs-Link|us_destroyer_porter_1942}}{{-}}{{Specs-Link|us_destroyer_porter_1944}}{{-}}{{Specs-Link|us_destroyer_somers_davis}}
{{Navigation-Line| }}{{Specs-Link|us_destroyer_fletcher}}{{-}}{{Specs-Link|us_destroyer_fletcher_bennion}}{{-}}{{Specs-Link|us_destroyer_fletcher_cowell}}{{-}}{{Specs-Link|us_destroyer_sumner}}{{-}}{{Specs-Link|us_destroyer_gearing}}{{-}}{{Specs-Link|us_destroyer_gearing_frank_knox}}{{-}}{{Specs-Link|us_destroyer_mitscher}}
{{Navigation-Line| }}{{Specs-Link|uk_destroyer_clemson_churchill}}{{-}}{{Specs-Link|uk_destroyer_v_class_verdun}}{{-}}{{Specs-Link|uk_destroyer_v_class_vega}}{{-}}{{Specs-Link|uk_destroyer_g_garland}}{{-}}{{Specs-Link|uk_destroyer_hunt_2series}}{{-}}{{Specs-Link|uk_destroyer_j_class}}{{-}}{{Specs-Link|uk_destroyer_n_class}}{{-}}{{Specs-Link|uk_destroyer_tribal}}
{{Navigation-Line| }}{{Specs-Link|fr_destroyer_hunt_3series}}{{-}}{{Specs-Link|fr_destroyer_jaguar_class_leopard}}{{-}}{{Specs-Link|fr_destroyer_le_fantasque_class_le_malin}}{{-}}{{Specs-Link|fr_destroyer_le_fantasque_class_le_triomphant}}

{{Navigation-Line|'''Light cruisers'''}}{{Specs-Link|us_cruiser_omaha_class_raleigh}}{{-}}{{Specs-Link|us_cruiser_omaha_class_detroit}}{{-}}{{Specs-Link|us_cruiser_brooklyn_class_helena}}{{-}}{{Specs-Link|us_cruiser_cleveland_class_cleveland}}{{-}}{{Specs-Link|us_cruiser_worcester_class_roanoke}}
{{Navigation-Line| }}{{Specs-Link|uk_cruiser_enterprise_d52}}{{-}}{{Specs-Link|uk_cruiser_leander}}{{-}}{{Specs-Link|uk_cruiser_arethusa}}{{-}}{{Specs-Link|uk_cruiser_dido}}
{{Navigation-Line| }}{{Specs-Link|fr_cruiser_dugauy_class_dugauy_trouin}}{{-}}{{Specs-Link|fr_cruiser_jeanne_darc}}

{{Navigation-Line|'''Heavy cruisers'''}}{{Specs-Link|us_cruiser_portland_class}}{{-}}{{Specs-Link|us_cruiser_baltimore_class}}
{{Navigation-Line| }}{{Specs-Link|uk_cruiser_hawkins}}{{-}}{{Specs-Link|uk_cruiser_london}}{{-}}{{Specs-Link|uk_cruiser_norfolk}}{{-}}{{Specs-Link|uk_cruiser_york}}

{{Navigation-Line|'''Battlecruisers'''}}{{Specs-Link|us_battlecruiser_alaska_class}}
{{Navigation-Line| }}{{Specs-Link|uk_battlecruiser_renown}}

{{Navigation-Line|'''Battleships'''}}{{Specs-Link|us_battleship_arkansas}}{{-}}{{Specs-Link|us_battleship_texas}}{{-}}{{Specs-Link|us_battleship_nevada}}
{{Navigation-Line| }}{{Specs-Link|fr_battleship_bretagne_class_lorraine}}
{{Navigation-End}}

== General info ==
<!-- ''Tell us about the tactical and technical characteristics of the cannon or machine gun.'' -->
The 20 mm/70 Oerlikon Mk.II features a belt-fed mechanism that allows for rapid fire rates of up to 450 rounds per minute. Its lightweight and compact design made it ideal for use on various naval vessels, including destroyers, cruisers, and battleships. Its versatility also allowed it to be mounted on ground vehicles, making it a popular choice for anti-aircraft defence.

=== Available ammunition ===
<!-- ''Describe the shells that are available for the weapon and their features and purpose. If it concerns autocannons or machine guns, write about different ammo belts and what is inside (which types of shells).'' -->

; Ground vehicles

* '''Default:''' {{Annotation|AP-T|Armour-piercing tracer}}{{-}}{{Annotation|HEF-I|High-explosive fragmentation incendiary}}{{-}}{{Annotation|AP-T|Armour-piercing tracer}}
* '''HET:''' {{Annotation|HEFI-T|High-explosive fragmentation incendiary tracer}}{{-}}{{Annotation|HEF-I|High-explosive fragmentation incendiary}}{{-}}{{Annotation|HEF-I|High-explosive fragmentation incendiary}}
* '''APT:''' {{Annotation|AP-T|Armour-piercing tracer}}

{{:Oerlikon Mk.II (20 mm)/Ammunition|HEF-I, AP-T, HEFI-T, HET HEF-I}}

; Naval vessels

* '''Universal:''' {{Annotation|HEF-T|High-explosive fragmentation tracer}}{{-}}{{Annotation|HEF-I|High-explosive fragmentation incendiary}}{{-}}{{Annotation|AP-T|Armour-piercing tracer}}
* '''20 mm HE:''' {{Annotation|HEF-T|High-explosive fragmentation tracer}}{{-}}{{Annotation|HEF-I|High-explosive fragmentation incendiary}}{{-}}{{Annotation|AP-T|Armour-piercing tracer}}{{-}}{{Annotation|HEF-I|High-explosive fragmentation incendiary}}
* '''20 mm AP:''' {{Annotation|AP-T|Armour-piercing tracer}}{{-}}{{Annotation|AP-T|Armour-piercing tracer}}{{-}}{{Annotation|AP-T|Armour-piercing tracer}}{{-}}{{Annotation|HEF-I|High-explosive fragmentation incendiary}}

{{:{{PAGENAME}}/Ammunition|HEF-T, AP-T, HEF-I}}

=== Comparison with analogues ===
''Give a comparative description of cannons/machine guns that have firepower equal to this weapon.''

== Usage in battles ==
''Describe the cannon/machine gun in the game - its distinctive features, tactics of usage against notable opponents. Please don't write a "guide" - do not impose a single point of view, but give the reader food for thought.''

=== Pros and cons ===
<!--''Summarise and briefly evaluate the weaponry in terms of its characteristics and combat effectiveness. Mark pros and cons as a list.''-->

'''Pros:''' 

* Fast rate of fire for a 20 mm.
* Will destroy aircraft quickly, even if using armour-piercing rounds.

'''Cons:'''

* Really poor penetration on the armour-piercing rounds for a 20 mm.

== History ==
<!-- ''Examine the history of the creation and combat usage of the weapon in more detail than in the introduction. If the historical reference turns out to be too long, take it to a separate article, taking a link to the article about the weapon and adding a block "/History" (example: <nowiki>https://wiki.warthunder.com/(Weapon-name)/History</nowiki>) and add a link to it here using the <code>main</code> template. Be sure to reference text and sources by using <code><nowiki><ref></ref></nowiki></code>, as well as adding them at the end of the article with <code><nowiki><references /></nowiki></code>.'' -->
The story of the Oerlikon begins in World War I with German industrialist Reinhold Becker who developed the Becker Type 2 20 mm cannon which used an advanced primer ignition blowback action. It saw limited use during World War I, but at the end of the conflict, the Treaty of Versailles forbade further production or development in Germany resulting in the design being sold to the Swiss firm SEMAG in 1919. In 1924, SEMAG went bankrupt and the design and staff was bought out by another Swiss arms company, Oerlikon. In the build-up that preceded World War II, the British Admiralty tested the Oerlikon gun in 1934 but rejected it. In 1937, they recognized that they needed a light anti-aircraft gun for armed merchant cruisers and smaller warships. In 1938, they ordered for a new Oerlikon variant with a better rate of fire and that would be easy to service and maintain for auxiliary crews. The changes were make and resulted in the Oerlikon Mark I getting adopted by the Royal Navy with a production license. The Mark II came about in 1940 when the Fall of France led to them producing the design under license due to loss of access to Switzerland, but the location of the buffer springs was different and changes were made to make it suitable for mass production. The first ship to be commissioned with this model was the HMS Duke of York in November of 1941. About 55,000 guns were in service in the UK and Commonwealth navies by 1945. It was also used by the British on their attempt at an self-propelled anti-aircraft vehicle: the [[Crusader AA Mk II]]. However it didn't see much service due to the Luftwaffe (German Air Force) being almost non-existent by 1944.

This design also saw service in the United States Navy. The first two models were Model 1934s purchased for evaluation in 1937, but like with the Royal Navy, they were initially rejected. However, by 1940, the growing threat of the war led the Navy to reconsider and seek a one-to-one replacement for the [[AN-M2 (12.7 mm)|AN-M2 Browning]] machine gun in the anti-aircraft. The Oerlikon thus entered widespread service by 1942 and would remain the main anti-aircraft gun of the US Navy until the introduction of the [[Bofors (40 mm) (Family)|Bofors (40 mm)]] by late 1943. Loved by its crews for its ease of maintenance and high rate of fire, the Oerlikon Mark 2 in US service claimed 32% of all Japanese aircraft downed by the navy between the United States entry into the war in December 1941, to September of 1944. However, by September, the Japanese began engaging in kamikaze attack and the 20 mm Oerlikon was insufficient to stop these attacks leading to the Bofors being used to replace it. The Oerlikon remains in service today as a weapon for repelling boarders.

== Media ==
''Excellent additions to the article would be video guides, screenshots from the game, and photos.''

== See also ==
''Links to the articles on the War Thunder Wiki that you think will be useful for the reader, for example:''

* ''reference to the article about the variant of the cannon/machine gun;''
* ''references to approximate analogues by other nations and research trees.''

== External links ==
''Paste links to sources and external resources, such as:''

* ''topic on the official game forum;''
* ''other literature.''

{{Britain and USA anti-aircraft guns}}
{{USA naval cannons}}
{{Britain naval cannons}}
{{Japan naval cannons}}
{{Italy naval cannons}}
{{France naval cannons}}

[[Category:Anti-aircraft guns]]
[[Category:Naval cannons]]