20 mm/70 Oerlikon Mk.II (20 mm)

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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

Vehicles equipped with this weapon
SPAA  AEC AA · Crusader AA Mk II
Motor torpedo boats  PT-103 · PT-109 · PT-174 · PT-314 · Thunderbolt (PT-556) · PT-565 · PT-71 · PT-200 · PT-658
  MTB Vosper(2) · MTB-422
Motor gun boats  Kim Qui · LCS(L)(3) · PTF-7 · USS Candid
  Fairmile B (ML345) · Fairmile C (332) · ML 1383 · SGB Grey Fox · SGB Grey Goose
Armoured gun boats  LCM(6) Zippo
Gunboats  HMS Spey
Sub-chasers  SC-497 · PC-451 · Carmi (PC-466)
  HMCS Brantford · HMS Liscomb
Frigates  USS Hoquiam
Destroyers  USS Barker · USS Aylwin · USS Fletcher · USS Bennion · USS Cowell
  USS Moffett · USS Phelps · USS Sumner · USS Gearing · USS Frank Knox · USS Mitscher · USS Davis
  HMS Churchill · HMS Vega · HMS Verdun
  ORP Garland · HMS Calpe · HMS Jervis · HMS Nepal · HMS Eskimo
Light cruisers  USS Cleveland · USS Detroit · USS Helena
  USS Raleigh · HMNZS Leander · HMS Arethusa · HMS Dido · HMS Enterprise
Heavy cruisers  USS Portland · USS Baltimore
  HMS Hawkins · HMS London · HMS Norfolk · HMS York
Battlecruisers  USS Alaska
Battleships  USS Nevada

General info

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

  • Universal: HEF-T · HEF-I · AP-T
  • 20 mm HE: HEF-T · HEF-I · AP-T · HEF-I
  • 20 mm AP: AP-T · AP-T · AP-T · HEF-I
Penetration statistics
Ammunition Penetration @ 0° Angle of Attack (mm)
10 m 100 m 500 m 1,000 m 1,500 m 2,000 m
HEF-T 2 2 2 2 2 2
AP-T 34 32 24 17 12 8
HEF-I 2 2 2 2 2 2
Shell details
Ammunition Velocity
mass (kg)
Fuse delay
Fuse sensitivity
Explosive mass
(TNT equivalent) (g)
0% 50% 100%
HEF-T 830 0.12 0 0.1 6.57 79° 80° 81°
AP-T 830 0.12 N/A N/A N/A 47° 60° 65°
HEF-I 830 0.12 0 0.1 11.17 79° 80° 81°

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.




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 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) 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.


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

See also

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

External links

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  • other literature.

Britain and USA anti-aircraft guns
7.92 mm  BESA
12.7 mm  M2HB
20 mm  GAI C01 · M168 · Oerlikon Mk.II · Polsten
25 mm  GAU-12U
30 mm  HSS 831L
35 mm  GA-35 · Oerlikon KDA
37 mm  M1A2
40 mm  Bofors L/60 · Dual Automatic Gun M2 · M266

USA naval cannons
20 mm  20 mm/70 Oerlikon Mk.II · 20 mm/70 Oerlikon Mark V · 20 mm/70 Oerlikon Mark 24
25 mm  25 mm/87 Mk.38
28 mm  1.1 inch/75 Mk.1
37 mm  AN-M4
40 mm  Bofors L/60 Mark 1 · Bofors L/60 Mark 2 · Bofors L/60 Mark 3
76 mm  3 inch/23 Mk.4 · 3-inch/50 Mk.10 · 3-inch/70 Mk.37 · 3-inch Mark 10 · 3 inch Mk.33 · 3-inch Mk.34
102 mm  4 inch/50 Mk.9
127 mm  5 inch/25 Mk.11 · 5 inch/25 Mk.13 AA · 5 inch/38 Mk.12 · 5-inch/50 Mk.5 · 5 inch/51 Mk.7 · 127 mm/54 Mark 18
152 mm  6 inch/47 Mk.16 · 6 inch/53 Mk.12
203 mm  8 inch/55 Mark 9 · 8 inch/55 Mark 12 · 8 inch/55 Mark 14 · 8 inch/55 Mark 16
305 mm  12-inch/45 Mk.5 · 12 inch/50 Mk.7 · 12 inch/50 Mk.8
356 mm  14 inch/45 Mk.8 · 14 inch/45 Mk.12

Britain naval cannons
20 mm  20 mm/70 Oerlikon Mk.II · 20 mm/70 Oerlikon Mark V · 20 mm/70 Oerlikon Mark 24
40 mm  2pdr QF Mk.IIc · 2pdr QF Mk.VIII · 2pdr Rolls Royce · QF Mark V · QF Mark VII · QF STAAG Mark II
47 mm  3 pdr QF Hotchkiss
57 mm  6pdr 7cwt QF Mk IIA · 6pdr QF Mk.V
76 mm  3 inch 12pdr 12 cwt QF Mk.V · 3 inch/70 Mark 6 · 76 mm/45 QF 3in 20cwt HA Mark I · 76 mm/50 12pdr 18cwt QF Mark I · OQF 3in 20cwt
102 mm  4 inch/40 QF mark III · 4 in QF Mark V · 4 inch/45 Mark XVI · 4 inch/50 BL Mark VII · BL Mark IX
114 mm  4.5 inch/45 QF Mark IV · 4.5 inch/45 QF Mark V · 8cwt QF Mk I
120 mm  4.7 inch/45 Mk.XII
133 mm  5.25 inch/50 QF Mark I
152 mm  6 inch/45 BL Mark VII · 6 inch/45 BL Mark XII · 6 inch/50 BL Mark XXIII · 6 inch/50 QF Mark N5
190 mm  7.5 inch/45 BL Mk.VI
203 mm  8 inch/50 Mark VIII
305 mm  305 mm/45 Mark X · 12 inch/50 Mark XI
343 mm  13.5 inch/45 Mark 5(H)
381 mm  15 inch/42 BL Mark I
20 mm  Rh202 (Germany)
40 mm  Bofors L/60 Mark 2 (USA) · Bofors L/60 Mark 3 (USA)
76 mm  76 mm/62 OTO-Melara Compact (Italy)