View source for Vickers 40 mm Class S gun

{{Short description|40 mm ground attack aircraft cannon}}
{{More citations needed|date=December 2007}}
{{Use dmy dates|date=May 2017}}
{{Use British English|date=May 2017}}
{{Infobox weapon
|name=Vickers 40 mm Class S
|image=Pilot 6 Sqn RAF with Hurricane IID at Shandur c1942.jpg
|caption= 1942. A [[Hawker Hurricane]] fitted with two Vickers S, at Shandur, Egypt.
|origin=
|type= 
|is_ranged=yes
|is_UK=yes
|design_date=
|production_date=1942
|service=1942-
|used_by=Royal Air Force
|wars=Second World War
|spec_type=
|caliber={{convert|40|mm|in|abbr=on}}
|part_length={{convert|1.7|m|ftin|abbr=on|disp=flip}}
|cartridge_weight={{convert|4|lb|kg|abbr=on}} 
|cartridge=40x158R
|feed=12-round drum<br/>later 15 rounds
|action=
|rate=100 rounds/min
|velocity=1,870 ft/s (570 m/s)<br>with {{cvt|3|lb|kg}} shot 
|weight={{convert|320 |lb|kg|abbr=on}}
|length=9 ft 9 inches (2.97 m)
|variants=Mk 1, Mk 2
|number=
}}

The '''Vickers 40&nbsp;mm Class S gun''',<ref>{{cite web |title=Vickers Class S |url=http://www.airwar.ru/weapon/guns/class_s.html |website=airwar.ru |access-date=2022-12-20}}</ref>{{efn|The name of the gun is spelled differently throughout sources. Compare with the [[QF 6pdr Class M Mark I with Auto Loader Mk III]].<ref>{{Cite web |title=The 6 pdr 7 cwt and the Molins Gun |first=Anthony G |last=Williams |date=7 January 2016 |url=https://www.quarryhs.co.uk/Molins.htm |url-status=dead |access-date=2021-08-14 |website=quarryhs.co.uk |archive-date=21 February 2021 |archive-url=https://web.archive.org/web/20210221185618/https://www.quarryhs.co.uk/Molins.htm }}</ref>|group=Note}} also known simply as the '''Vickers S''' or '''S gun''',<ref name=Goodrum>{{cite book |first= Alastair |last=Goodrum |title= They Spread Their Wings: Six Courageous Airmen in Combat in the Second World War |url=https://books.google.com/books?id=Ps8TDQAAQBAJ&pg=PT23 |page=23 |publisher= The History Press |date=2013|isbn=9780752492179 }}</ref> was a 40&nbsp;mm (1.57&nbsp;in) airborne [[autocannon]] designed by [[Vickers-Armstrongs]] for use as aircraft armament.

It was primarily used during [[World War II]] by British aircraft to attack ground targets.<ref>{{Cite web|first=Anthony G|last=Williams|title=The Vickers 40 mm Class S Gun With Littlejohn Adaptor|url=https://www.quarryhs.co.uk/sgun.htm|access-date=2021-08-14|website=quarryhs.co.uk|archive-date=21 October 2021|archive-url=https://web.archive.org/web/20211021234819/https://www.quarryhs.co.uk/sgun.htm|url-status=dead}}</ref> It was largely replaced by the [[RP-3]] rocket from 1943 on.

== Development ==
The Vickers 40&nbsp;mm Class S gun was developed in the late 1930s as defensive weapon for bomber aircraft. The [[ammunition]] was based on the 40x158R cartridge case of the 40 mm [[QF 2-pounder naval gun|naval QF 2-pounder anti-aircraft gun]] (known as the "pom-pom"). The gun itself was derived from the [[COW 37 mm gun|Coventry Ordnance Works 37 mm gun]] which used a [[Long recoil#Long recoil operation|long-recoil operation]] to fire a {{convert|1.5|lb|abbr=on}} projectile.

The gun was the planned armament of the Vickers Type 414 twin-engined fighter proposed to the [[Air Ministry]] in response to [[List of Air Ministry specifications|specification F6/39]] for a two-seat fighter with 20mm cannon and the option of upgrading to 40mm guns. The Type 414 design placed the gun in a flexible mount in the nose, the gun linked to a range-finding predictor gunsight for the aircraft's gunner sat next to the pilot. The Air Ministry raised specification F22/39 for the design with two prototypes planned to test the gun and gunsight. The [[Vickers Wellington]] II prototype (serial ''L4250'') was converted with the gun and gunsight in a dorsal turret. The armament was first flown on 25 October 1940 and test fired against a target (towed by a [[Hawker Henley]] target tug) on 8 November. The estimate was 50% of shells were within 4 ft of the target. {{Sfn|Buttler|2004|p=p43}}  

In March 1941, researchers with the [[Fighter Interception Unit]] at [[RAF Tangmere]] fitted the fourth prototype Mk I [[Bristol Beaufighter]] night fighter{{efn|military serial number ''R2055''}} with the Vickers&nbsp;S, installed asymmetrically, in the place of one of the standard 20&nbsp;mm cannon. In August, the [[Rolls-Royce 40 mm cannon]] ("R" model) was also trialled in the same Beaufighter. Both cannons were assessed when fired in the air and on the ground. In October, the Vickers&nbsp;S was recommended for any future service use, although it was never incorporated into production Beaufighters. The reasons for this have remained unclear, although it may have reflected the perception that a single 40&nbsp;mm cannon lacked advantages over the 4x20&nbsp;mm configuration.

[[Hawker Hurricane]]s, fitted with two Vickers&nbsp;S were trialled though not initially adopted in [[North African campaign|North Africa campaign]] as anti-tank armament.

The gun was considered for improving the armament of [[RAF Coastal Command|Coastal Command]] aircraft which were being lost to surfaced submarines from 1943. The [[Short Sunderland]] aircraft had only a few machine guns to the front which were outranged by the submarines [[2 cm Flak 30, Flak 38 and Flakvierling 38|20 mm]] and 37 mm cannon. Coastal Command [[Boeing B-17 Flying Fortress|Boeing B-17 Fortress]] IIA ''FK185'' was modified with an all-electric B.16 mounting built by [[Bristol Aeroplane Company|Bristol]] installed in the nose.  In tests against an old ship in June 1944, armour-piercing ammunition went through two 0.5 inch and a 0.375 plates. By this point of the war the submarine threat had been reduced and RP-3 rockets were proven to be more effective against submarines.{{sfn|Clarke|1993|pp=43–44}}

== Combat history ==
Early operations by the [[Desert Air Force]] in the North Africa campaign demonstrated that existing weapons were ineffective against newer German vehicles like the [[Panzer III]] medium tank. In April 1941 a group formed to study the issue, considered a series of 37 and 40&nbsp;mm weapons including the "S", the Rolls-Royce cannon (belt fed variant), and the US-built [[M4 autocannon]], all firing [[armour-piercing]] ammunition.<ref name="Wallace,1972">{{cite book|last=Wallace|first=G.F.|title=The Guns of the Royal Air Force 1939-1945|publisher=William Kimber|location=London|year=1972|isbn=0-7183-0362-8|chapter=10, The 40mm Guns}}</ref>{{page needed|date=October 2022}} The Rolls-Royce "BF" was initially selected, although it used drum-fed ammunition rather than the "S" belt system that was considered more reliable. About 200 BF guns were produced, but after a series of misfires and ammunition explosions,<ref name=Goodrum/>{{page needed|date=October 2022}} the decision was made to introduce [[ground attack]] variants of the Hawker Hurricane (designated [[Hawker Hurricane variants#Hurricane IID|Mark IID]]) with the "S". This had the added advantage that it carried 15 rounds of ammunition, compared to the "BF"'s 12.

Mark IID and Mark IV Hurricanes could mount one "S" under each wing, in conformal [[gun pod]]s. The weight of the guns and ammunition, along with the dust filters and other equipment needed for desert operations, slowed the aircraft by a significant {{convert|40|mph|abbr=on}}. By October 1941 it was decided that the autocannon would not be suitable in the future, and the same research group turned their attention to rockets, eventually leading to the introduction of the [[RP-3]] in 1943.

The weapon was cleared for service on the Hurricane in April 1942 and formed up with [[No. 6 Squadron RAF]] at RAF [[Heliopolis, Cairo|Shandur]] in [[Egypt]] in May. The weapon's champion, Wing Commander Stephen 'Dru' Drury, trained the pilots on using the weapon, as it had so much recoil that the aircraft slowed significantly when fired. This caused the nose to drop, and while flying at a typical altitude of {{convert|50|ft|abbr=on}} during the approach, firing without first re-adjusting the flight path was dangerous. The pilots eventually concluded that the guns could be fired twice before the aircraft flew past the target, although on rare occasions a third shot was possible.<ref name=Goodrum/>{{page needed|date=October 2022}}

Claims by pilots using the Vickers S included 47 tanks destroyed (of 148 tanks hit), as well as nearly 200 other vehicles. However, the Hurricane IID was poorly protected for the ground attack role and ground fire caused heavy losses. Mark IV Hurricanes - operational from 1943 - had improved armour around their engine, cockpit and fuel tanks. In addition, 40&nbsp;mm ammunition was seldom effective against vehicles as well-armoured as the [[Tiger I]] heavy tank.

From 1944, Hurricanes armed with the Vickers S served in the [[South-East Asian theatre of World War II|South East Asian theatre]]. In most cases [[High explosive|HE]] ammunition was used against road vehicles and rivercraft.

Assessments carried out in South East Asia showed a relatively high level of accuracy: an average of 25% of shots fired at tanks hit their target. By comparison, "60 lb" RP-3 rocket projectiles only hit 5% against tank-sized targets. However, 40&nbsp;mm HE rounds were twice as accurate as AP rounds, possibly because the lower weight and higher velocity of the HE round gave it ballistics similar to that of the .303 in (7.7 mm) [[M1919 Browning machine gun|Browning machine gun]]s that were used for sighting.

== Comparable weapons ==
Comparable contemporary aircraft weapons:

;Germany
* [[MK 101 cannon|30&nbsp;mm MK 101]]
* [[MK 103 cannon|30&nbsp;mm MK 103]]
* [[BK 3,7|37&nbsp;mm BK 3,7]]
* [[Rheinmetall BK-5|50&nbsp;mm BK 5]]
* [[MK 214A cannon|50&nbsp;mm MK 214A]] (experimental)

;Japan
* [[Ho-203 cannon|37&nbsp;mm Ho-203]]
* [[Ho-204 cannon|37&nbsp;mm Ho-204]]
* [[Ho-401 cannon|57&nbsp;mm Ho-401]]

;Soviet Union
* [[Nudelman-Suranov NS-37|37&nbsp;mm NS-37]]
* [[Nudelman-Suranov NS-45|45&nbsp;mm NS-45]]

;Sweden
* [[Bofors 57 mm m/47 aircraft gun|57 mm akan m/47]]

;United Kingdom
* [[Rolls-Royce 40 mm cannon|40&nbsp;mm Class BH gun]] (experimental)
* [[Vickers 47 mm Class P gun|47&nbsp;mm Class P gun]] (experimental)
* [[Ordnance QF 6-pounder|57&nbsp;mm QF 6-pounder Class M gun]]

== Footnotes ==
{{notelist}}

== References ==

=== Citations ===
{{reflist}}
* {{Cite book |last=Buttler |first=Tony |title=Fighters and Bombers 1935-1950 |date=2004 |publisher=Midland Publishing |isbn=9781857801798 |series=British Secret Projects 3}}
* {{cite book |last=Clarke |first=R. Wallace |title=British Aircraft Armament |date=1993 |publisher=Patrick Stephens}}

== External links ==
{{Commons category|Vickers S}}
* [http://www.quarryhs.co.uk/37-40mm.htm 37 mm and 40 mm guns in British Service by Anthony G Williams] {{Webarchive|url=https://web.archive.org/web/20200203213225/http://quarryhs.co.uk/37-40mm.htm |date=3 February 2020}}

[[Category:40 mm artillery]]
[[Category:Aircraft artillery]]
[[Category:Vickers]]
[[Category:Autocannon]]
[[Category:Anti-tank weapons]]
[[Category:Weapons and ammunition introduced in 1942]]