The 20mm Hispano-Suiza HS.820 is a Swiss 20x139mm autocannon developed by Hispano-Suiza and later sold as the Oerlikon KAD after the armaments line moved to Oerlikon-Contraves. Sources document the family through anti-aircraft mounts, 20x139mm ammunition, and the U.S. M139 designation carried by the M114A2 reconnaissance carrier, but this entry stays relationship-only until exact conflict-use sourcing for the cannon is stronger.
The HS.820 family appears in source material as a cannon used across single guns, twin anti-aircraft mounts, vehicle cupolas, and related 20x139mm ammunition programs. The strongest current evidence supports those system relationships rather than a standalone conflict-use row for the exact cannon.
Hispano-Suiza HS.820 became Oerlikon KAD after the armaments line moved to Oerlikon-Contraves; M139 is listed as the U.S. service designation.
Weaponsystems.net identifies the HS.666A / GAI-D01 twin mount, HS-30, M3 VDAA, and VAB VDAA as applications using HS.820 or KAD cannon.
A U.S. Army image shows an M114A2 Command and Reconnaissance Carrier with an M139 20 mm cannon, while AFV Database identifies M139 as the U.S. designation for the Hispano-Suiza HS.820.
The 1962 Rheinmetall booklet lists practice tracer, high-explosive incendiary tracer, and armor-piercing tracer ammunition for MK 20mm HS 820 automatic guns; Chinn separately treats M139/HS.820 ammunition as part of the U.S. rapid-fire vehicle-weapon context.
Sources: Weaponsystems.net 20mm Hispano-Suiza HS.820; MK 20mm HS 820 Ammunition; The Machine Gun Volume V; File:M114A2 Command and Reconnaissance Carrier.jpg; AFV Database M114.
The HS.820 designation covers the original Hispano-Suiza gun, later Oerlikon KAD naming, U.S. M139 service designation, and several single, twin, and vehicle mount applications.
| Variant | Configuration | Designation notes |
|---|---|---|
| HS.820 | Original Hispano-Suiza autocannon | Weaponsystems.net identifies the HS.820 as a Swiss 20x139mm autocannon developed in the late 1940s and entering service in the early 1950s. |
| Oerlikon KAD | Post-acquisition Oerlikon designation | The same source lists KAD as the Oerlikon product-line designation after acquisition, with Oerlikon-Contraves production from 1970. |
| M139 | U.S. service designation | Weaponsystems.net lists M139 as the U.S. service designation, and a U.S. Army image identifies an M114A2 Command and Reconnaissance Carrier with an M139 20 mm cannon. Sources: Weaponsystems.net 20mm Hispano-Suiza HS.820, File:M114A2 Command and Reconnaissance Carrier.jpg |
| HS.666A / GAI-D01 | Twin anti-aircraft mount | Weaponsystems.net describes the Hispano-Suiza HS.666A twin mount as armed with two HS.820 cannon and later renamed GAI-D01 with KAD cannon after the Oerlikon-Contraves acquisition. |
Source-backed carrier relationships show how the HS.820/KAD family moved from the cannon designation into vehicle and air-defense installations.
| Carrier | Carrier type | Carriage evidence |
|---|---|---|
 | Tracked reconnaissance carrier | AFV Database identifies the M139 20 mm automatic gun as the U.S. designation for the Hispano-Suiza HS.820 and says it armed the M114A1E1/M114A2 configuration. Sources: AFV Database M114, File:M114A2 Command and Reconnaissance Carrier.jpg |
 | 4x4 air-defense vehicle branch | Weaponsystems.net identifies the M3 VDAA as using a TA-20 turret with two HS.820 or KAD cannon on a Panhard M3 chassis. Sources: VDAA |
 | 4x4 armored carrier air-defense branch | Weaponsystems.net identifies the VAB VDAA as a VAB-based application using the same TA-20 turret and two HS.820 or KAD cannon. Sources: VDAA |
Weaponsystems.net places HS.820 production from 1949 onward, with Hispano-Suiza production before the 1970 Oerlikon-Contraves period.
Sources: Weaponsystems.net 20mm Hispano-Suiza HS.820
Weaponsystems.net lists early-1950s service entry for the 20 mm HS.820 / KAD autocannon family.
Sources: Weaponsystems.net 20mm Hispano-Suiza HS.820
A March 1962 Rheinmetall ammunition booklet lists MK 20mm HS 820 practice, high-explosive incendiary tracer, and armor-piercing tracer cartridge types for AA and infantry use.
Sources: MK 20mm HS 820 Ammunition
Weaponsystems.net separates Hispano-Suiza production up to 1970 from Oerlikon-Contraves production after 1970 and lists Oerlikon KAD as the post-acquisition product-line name.
Sources: Weaponsystems.net 20mm Hispano-Suiza HS.820
A public-domain U.S. Army image reproduced on Wikimedia Commons identifies a Hispano-Suiza 820L 20 mm gun in a towed system presentation from the Fiscal Year 1974 authorization material.
Sources: File:Hispano-Suiza & Vulan 20mm towed systems.png
