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

One of the two 20 mm/70 Oerlikon Mk.II on the stern of HMAS Nepal

Description

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.

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

Ground vehicles

• Default: AP-T · HEF-I · AP-T
• HET: HEFI-T · HEF-I · HEF-I
• APT: AP-T

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-I	4	4	3	3	3	3
AP-T	38	35	23	14	9	5
HEFI-T	4	4	3	3	3	3

Shell details
Ammunition	Velocity (m/s)	Projectile mass (kg)	Fuse delay (m)	Fuse sensitivity (mm)	Explosive mass (TNT equivalent) (g)	Ricochet
						0%	50%	100%
HEF-I	838	0.12	0	0.1	6	-	-	-
AP-T	830	0.14	-	-	-	47°	60°	65°
HEFI-T	838	0.12	0.1	0.1	5	79°	80°	81°
HEF-I (HET)	838	0.12	0.1	0.1	5	79°	80°	81°

Naval vessels

• 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 (m/s)	Projectile mass (kg)	Fuse delay (m)	Fuse sensitivity (mm)	Explosive mass (TNT equivalent) (g)	Ricochet
						0%	50%	100%
HEF-T	830	0.12	0	0.1	6.57	79°	80°	81°
AP-T	830	0.12	-	-	-	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

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

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.

Media

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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• topic on the official game forum;
• 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
37 mm	M1A2
40 mm	Bofors L/60 · Dual Automatic Gun M2 · M266
	Foreign:
23 mm	ZU-23 (USSR)
35 mm	Oerlikon KDA (Swiss)

Japan naval cannons
20 mm	JM61 · Type 98
25 mm	25 mm/60 Type 96
37 mm	Type 4 · Type 11 pattern 1922
40 mm	40 mm/62 Vickers
57 mm	Type 97
75 mm	Type 88 AA
76 mm	3-inch/40 Type 41 · 8 cm/40 3rd Year Type · 8 cm/60 Type 98
100 mm	100/65 mm Type 98 mod A
120 mm	120 mm/45 3rd Year Type · 120 mm/45 10th year type
127 mm	5 inch/40 Type 89 · 127 mm/50 3rd Year Type
140 mm	140 mm/50 3rd Year Type
152 mm	6-inch/45 Type 41 · 15 cm/50 Type 41
155 mm	155 mm/60 3rd Year Type
200 mm	20 cm 3rd year type No.1
203 mm	20 cm/45 Type 41 · 20 cm/50 3rd year type No.2
356 mm	36 cm/45 Type 41
410 mm	410 mm/45 Type 3
	Foreign:
20 mm	20 mm/70 Oerlikon Mk.II (USA/Britain)
40 mm	Bofors L/60 Mark 1 (USA) · Bofors L/60 Mark 2 (USA) · Bofors L/60 Mark 3 (USA)
47 mm	3 pdr QF Hotchkiss (Britain)
76 mm	3-inch Mark 10 (USA) · 3 inch Mk.33 (USA) · 3-inch Mk.34 (USA)
120 mm	4,7-inch/40 Armstrong (Britain)
127 mm	5 inch/38 Mk.12 (USA)
305 mm	12-inch/45 Vickers (Britain) · 12-inch/50 Vickers (Britain)

France naval cannons
37 mm	37 mm/50 model 1925 · 37 mm/50 model 1933
47 mm	3 pdr QF Hotchkiss
57 mm	57 mm/60 ACAD Mle 1951
75 mm	75 mm/50 Canet model 1891 · 75 mm/50 model 1922
90 mm	90 mm/50 model 1926
130 mm	130 mm/40 model 1919
138.6 mm	138.6 mm/55 model 1910 · 138.6 mm/40 model 1927 · 138.6 mm/50 model 1929 · 138.6 mm/50 model 1934 R1938
152 mm	152 mm/55 model 1930
155 mm	155 mm/50 model 1920
203 mm	203 mm/50 model 1924
305 mm	305 mm/45 model 1906-10
340 mm	340 mm/45 model 1912
	Foreign:
20 mm	2 cm/65 C/38 (Germany) · 2 cm/65 Flakvierling 38 (Germany) · 20 mm/70 Oerlikon Mk.II (USA/Britain)
40 mm	2pdr QF Mk.IIc (Britain) · 2pdr QF Mk.VIII (Britain) · Bofors L/60 Mark 2 (USA) · Bofors L/60 Mark 3 (USA)
87.6 mm	Ordnance QF 25pdr (87.6 mm) (Britain)
102 mm	4 in QF Mark V (Britain) · 4 inch/45 Mark XVI (Britain)
105 mm	SK C/33 AA (Germany)
128 mm	12.8 cm/45 SK C/34 (Germany)
150 mm	15 cm/48 KC/36 (Germany)