View source for Engineering:Hispano-Suiza HS.820

{{1r|date=November 2017}}
{{Infobox weapon
|name=HS.820
| image=File:Flab 20 mm IMG 1523.JPG
| image_size = 300
|caption=Swiss HS.820 in the HS.666A configuration.
|origin=Swiss
|type=[[Engineering:Autocannon|Autocannon]]
<!-- Type selection -->
|is_ranged=yes
|is_artillery=yes
<!-- Service history -->
|service=
|used_by=
|wars=
<!-- Production history -->
|designer=
|design_date=
|manufacturer=
|unit_cost=
|production_date=
|number=
|variants=
<!-- General specifications -->
|spec_label=
|weight={{convert|66|kg|lb|abbr=on}} (without ammunition)
|length={{convert|2489|mm|in|abbr=on}}
|part_length= {{convert|1727|mm|in|abbr=on}}
|width=
|height=
|diameter=
|crew=
<!-- Ranged weapon specifications -->
|cartridge=
|caliber=20×139mm
|action=Gas unlocked, delayed blowback
|rate=1000 round/min
|velocity={{convert|1050|m/s|ft/s|abbr=on}}
|range={{convert|1500|m|ft|abbr=on}} against aerial targets
|max_range=
|feed=
|sights=
<!-- Artillery specifications -->
|breech=
|recoil=
|carriage=
|elevation=
|traverse=
}}

The '''HS.820''' was a 20 mm caliber [[Engineering:Autocannon|autocannon]] developed by [[Company:Hispano-Suiza|Hispano-Suiza]] primarily for aircraft use, but more widely used in a series of ground-based anti-aircraft guns. After Oerlikon purchased Hispano's armaments division in 1970, the HS.820 became the '''Oerlikon KAD''', supplanting Oerlikon's own [[Engineering:Oerlikon 20 mm cannon#Gas-operated models|KAA and KAB]] weapons in the process.<ref>[http://www.janes.com/extracts/extract/jah/jah_0114.html 20 x 139 round (Switzerland)], Jane's Ammunition Handbook</ref> A US-built model, the '''M139''', saw some use on vehicles.

== Development ==
thumb|An armored vehicle [[Schützenpanzer SPz 11-2 Kurz equipped with a gun HS.820]]

Developed in the post-World War II era, the HS.820 fired a 20×139&nbsp;mm round developed from the Swiss 20×139 FMK (and FK 38) as a replacement for their earlier 20×110&nbsp;mm design of the widely used [[Engineering:Hispano-Suiza HS.404|HS.404]]. The new round was one of two post-WWII European 20&nbsp;mm designs, the other being the 20×128 developed by Oerlikon for a similar role.<ref>[http://www.quarryhs.co.uk/an_introduction_to_collecting_20.htm "An introduction to collecting 20 mm cannon cartridges"] {{Webarchive|url=https://web.archive.org/web/20210120211110/http://www.quarryhs.co.uk/an_introduction_to_collecting_20.htm |date=2021-01-20 }}, Anthony Williams</ref> The HS.820's high 1100&nbsp;m/s [[Physics:Muzzle velocity|muzzle velocity]] and equally high 1000 round per minute firing rate made it a formidable weapon. Nevertheless, the rapid introduction of even higher performance [[Engineering:Revolver cannon|revolver cannon]]s meant the HS.820 was never as popular in aircraft role as the HS.404 had been.

The weapon was more widely used in a variety of mounts for the anti-aircraft role, especially in naval use. Hispano introduced a number of mountings with a variety of sighting systems, feeds and power traverse. The '''HS.639-B3''' (later known as the '''GAI-CO1''') was a single-gun mounting fed from a 75-round drum, a fairly serious limitation for a gun with such a high rate of fire. Variants included the '''HS.639-B4''' ('''GAI-CO3''') with a 50-round drum mounted on top of the weapon, and the '''HS.639-B5''' ('''GAI-CO6''') that used dual 75-round magazines for longer firing times. The '''HS 665''' was a triple-mount variety using the same drum feeds. The '''HS.666A''' ('''GAI-DO1'''), developed in the mid-70s, featured two HS.820 with new 120-round box magazines mounted on a shared hydraulically powered platform which could be tied into an associated radar-guided fire-control system.<ref>''A Compendium of Armaments and Military Hardware'', Christopher Chant, {{ISBN|0-7102-0720-4}}</ref>

After Oerlikon purchased Hispano-Suiza, they undertook a renaming exercise for all of their weapons. The HS.820 was then known as the KAD, meaning ''Kanone'', A for 20&nbsp;mm{{efn|A for 20, B for 23 or 25, C for 30 and D for 35 mm.}} and D as the fourth model. Oerlikon's own 20×128&nbsp;mm became the KAA in the electrically-fired version, and the KAB in the gas-operated version.

The United States produced a slightly modified version of the HS.820 as the '''M139'''. It saw use on a number of vehicles, including the US Army's M114 and the Marine Corps Amphibious Assault Vehicle and the ill-fated MICV-65 series of armored vehicles, including on a palletised mount in the cabin of a Bell UH-1 helicopter.<ref name="pint">{{cite web|title=Vietnam War|url=https://www.pinterest.co.uk/pin/318911217348815571/?lp=true|website=Pinterest|accessdate=4 May 2018|language=en}}</ref>

The 20×139&nbsp;mm round was also widely used in a variety of other weapons, including the Rheinmetall MK 20 Rh 202 and [[Engineering:20 mm modèle F2 gun|20 mm modèle F2 gun]].

==Original Hispano-Suiza ammunition==
*UIA (HEI): Projectile weight 120 g, explosive filler 10 g
*RIA (APHEI): Projectile weight 120 g, explosive filler 4.5 g
*RINT (APHC): Projectile weight 111 g,  tungsten carbide core weight 70 g

==See also==
* [[Engineering:Hispano-Suiza HS.404|Hispano-Suiza HS.404]]
* [[Engineering:Oerlikon 20 mm cannon|Oerlikon 20 mm cannon]]
* [[Engineering:Rheinmetall Mk 20 Rh-202|Rheinmetall Mk 20 Rh-202]]
* Zastava M55
* [[Engineering:Oerlikon KCB|Oerlikon KCB]]
* [[Engineering:ZPU|ZPU]]
* [[Engineering:ZU-23-2|ZU-23-2]]

==Notes==
{{notelist}}

==References==
{{reflist}}

[[Category:Aircraft guns]]
[[Category:Autocannon]]

{{Sourceattribution|Hispano-Suiza HS.820}}