Oerlikon 35 mm twin cannon

The Oerlikon 35 mm twin cannon is a towed anti-aircraft gun made by Oerlikon Contraves (renamed as Rheinmetall Air Defence AG following the merger with Rheinmetall in 2009). The system was originally designated as 2 ZLA/353 ML but this was later changed to GDF-001. It was developed in the late 1950s and is used by around 30 countries.

Design & development
The system uses 35 mm auto cannons, which were originally designated 353 MK and are now designated as the KD series. The same KD series 35 mm cannons are used in the Leopard 1 based Gepard and Type 74 tank based Type 87 SPAAG and T-55 based Marksman self-propelled anti-aircraft guns. The system could be paired with the off-gun Super Fledermaus fire control radar, which in the late 1970s was upgraded to the Skyguard system.

In 1980 an upgraded model, the GDF-002 was produced, which featured an improved sight, and the ability to be directed by an off-gun digital control system. A few years later a third version of the system was being produced, the GDF-003, which was broadly similar to the GDF-002, but included some enhancements like self-lubricating weapons and integrated protective covers.

In 1985 a further upgraded model was produced, the GDF-005, which was introduced, featuring the Gunking 3D computer-controlled sight with an integrated laser range-finder and digital control system.

The guns are usually transported by a 5-tonne 6×6 truck.

KD series cannons
Development of the KD series cannon began around 1952 soon after Oerlikon calculated that 35 mm was the optimum calibre for an anti-aircraft gun. The KD series cannons were a design adapted from the post-war 20 mm KAA 204 Gk cannon. Several designs were developed, including a water cooled design, designated Mk 352, which was tested by the U.S. Navy. The final design was the Mk 323, which was developed in two variants, a belt fed version the KDA, and a linkless version the KDC, fed by five round clips. Both designs are gas operated with a propped lock locking system.

Super Fledermaus
The Super Fledermaus fire control system was designed and built by the then separate Contraves company. It consists of a four-wheeled towed trailer with an E/F band pulse doppler search radar with a range of around 15 km and a pulse doppler tracking radar operating in the J band, also with a range of 15 km. It was also used as the fire control system on the Gepard SPAAG.

Skyguard
The Skyguard system is contained within a towed trailer, mounted on the roof of which is a pulse doppler search radar, a pulse doppler tracking radar and a co-axial television camera. The trailer also houses the crew of two and a small petrol generator. Skyguard is an all-weather air defense system for the control of aircraft at low altitude and at low and medium altitude range up to 3,000 m. The maximum effect distance is given as 4,000 m. The system takes the air surveillance, target acquisition, calculation of the derivative-action values ​​and the control of two Oerlikon 35 mm anti-aircraft guns. Skyguard is served by four people.

It was created by Oerlikon-Buehrle. The weapon was introduced in the sixties in the Swiss Army and get updates in 1975, 1995 and 2010.. They are still in use. It had replaced the system Contraves Super Fledermaus in the Swiss Air Force. The Skyguard radar system was used in the German Air Force for surveillance of low-altitude flight zones. The radar unit is ready very quickly through the hydraulic systems for antenna construction and leveling after installation. A typical fire unit using the Skyguard consists of two twin 35 mm gun platforms with a single Skyguard fire control radar.

History

 * 1982: The system was widely used by Argentine forces during the Falklands War. The Skyguard radar system was employed by the 601 Antiaircraft Artillery Group and the Super Fledermaus by the 1st Group of the Argentinian Air Force. The Skyguard succeeded in shooting down a Sea Harrier (XZ450) on 4 May 1982 at Goose Green. This resulted in a shift of tactics, so that British aircraft largely operated outside the weapons system's range. An RAF Harrier (XZ988) was shot down by these cannons again over Goose Green on 27 May. The system was also employed in direct fire mode against British paratroopers during the Battle of Goose Green, killing two and wounding 11 and stopping the advance of two companies. The guns were involved in two deadly friendly fire incidents during the campaign. The first took place on 1 May 1982, when a GADA 601 battery fired three burst of 35 mm rounds at an Argentine  Mirage III attempting to make an emergency landing at Stanley, after the aircraft had been already targeted by Argentine Marine Hispano-Suiza HS-831 30mm guns deployed along the town. The aircraft fell in flames north of the airport, killing the pilot. The other friendly shootdown occurred at Goose-Green, when one A4 Skyhawk flew by mistake over a banned zone, and was shot down with the loss of the pilot. The Argentine Air Force conceded that this time the incident was triggered by the pilot's navigation error. The Skyguard radars were targeted by the RAF during Operation Black Buck on May 31 and June 3. One Skyguard radar was destroyed by shrapnel from a Shrike missile strike and four operators died as a result. Another Harrier (XW919) was presumably hit by 35 mm splinters over Sapper Hill on June 12 and sustained heavy damage.  The aircraft was later declared out of service. There was a further direct-fire mission conducted against British troops on Wireless Ridge, just hours before the Argentinian surrender. After being disabled by their operators the guns were captured by British forces. 15 guns and five Skyguard units were captured and later refurbished by BMARC in Britain. 12 guns and 4 Skyguard radars were put into British service operated by the Royal Auxiliary Air Force 2729 Squadron, based at RAF Waddington. The RAuxAF used these guns and radar for about 10 years but defence cuts forced disbanding of the very popular and reliable system.


 * 12 October 2007: Nine South African National Defence Force (SANDF) soldiers were killed and 14 injured by the system during a training exercise at the SANDF Battle School at Lohatla in the Northern Cape province. A line of 8 cannons were engaging a tank hulk in manual ground fire with the guns at low elevation and the maximum traverse of the barrels secured by safety poles and tethers. The rightmost gun jammed while firing and had to be repaired by technicians. Shortly after the gun was cleared to fire again, the gun malfunctioned, entered automatic mode, broke through the traversal-restriction safety mechanisms and began firing, striking the other guns along the firing line. Initial reports suggested that the malfunction was caused when the gun underwent an unexplained hang fire of the explosive 35mm ammunition in the magazines, causing the turret to swing uncontrolled through 360-degrees firing wildly until it exhausted its remaining ammo. A statement issued by the South African Defense Minister Mosiuoa Lekota, however, stated that the gun had inexplicably traversed 90-degrees to the left, breaking through the safety mechanisms, and fired only a 1/8 second long burst, striking all of the soldiers located on the right hand side of their guns.  The accident report published by the SANDF in January 2008 blamed "undetected mechanical failure—which the manufacturers of an anti-aircraft gun allegedly kept secret". The report says the gun malfunctioned because a spring pin, which is the size of a matchstick, sheared.  Other sources blamed poor training and safety procedures in the SANDF.

Ammunition

 * Designation:
 * HEI: High Explosive Incendiary (-T—Tracer)
 * SAPHEI: Semi-Armour Piercing High Explosive Incendiary
 * FAPDS: Frangible Armour Piercing Discarding Sabot
 * AHEAD: Anti-missile rounds, that fire "152 heavy tungsten metal sub-projectiles".
 * TP: Target Practice (-T—Tracer)

Versions

 * GDF-001 / '2 ZLA/353 MK: XABA sight
 * GDF-002: Introduced in 1980. Improved Ferranti sight and digital data bus. The gun has 112 rounds ready and 126 in reserve (238 rounds total)
 * GDF-003: Minor enhancements including protective covers and automatic weapon lubrication.
 * GDF-005: Introduced in 1985. Fitted with Gunking 3D computer controlled sight with a laser range finder and digital fire control system. Integrated power supply and diagnostics. 280 rounds on the gun and an automatic re-loading system.
 * GDF-006: GDF-001/002/003 upgraded with AHEAD system.
 * GDF-007: GDF-005 upgraded with AHEAD system.
 * AHEAD: An upgrade for the GDF series guns built around a special projectile which explodes at a pre-calculated point in front of the target sending a cone of 152 tungsten sub-projectiles at the target. Used by Canada, Pakistan, Greece, Oman, Spain, Taiwan and Chile (unconfirmed).
 * Gepard: Self-propelled version of the system based around the Leopard 1.
 * Marksman: Self-propelled version of the system based around the Marksman turret, which could be fitted on numerous tank chassies. The only model that went into production was a version based on the T-55 chassis for Finland, 7 systems in war reserve.
 * Type 87: Japanese SPAAG using the system.
 * PZA Loara: Polish SPAAG based on the PT-91 tank
 * Type 90 (PG99): Chinese licensed copy of GDF-002. The PG99 is a towed anti-aircraft gun suitable for point and coastal air defence. It is usually deployed near military bases, airfields, tunnels, islands, and along the coast to defend Sea Land of Communication (SLOC), ports, bridges and other important assets.
 * PG99 (CS/SA1): Chinese upgrade of GDF-002. Mounted on the 6 x 6 SX2190 truck, the PG99 (CS/SA1) is a self-propelled variant of the Type 90 35 mm AA system, previously available only as a towed AA piece.


 * Samavat: Iranian version of these guns with night vision sight and Used with Skyguard & Super Fledermaus FC radars.
 * Amoun: Egyptian version of Skyguard & Sparrow SAM.

Operators



 * 🇦🇷: 50+ GDF-002 units, XABA sight used
 * 🇦🇹: 74 GDF-005 Army, Air Force 18 GDF-005
 * 🇧🇭: 12 GDF-005 units
 * 🇧🇷: 38 GDF-001 with updated Super Fledermaus and Brazilian made Skyguard FC radars
 * 🇨🇲: 18+ GDF-002 units
 * 🇨🇦: 20 GDF-005 units and 10 Skyguard FC radars, to be phased out. AHEAD modified.
 * 24 GDF-005/007 units. gdf-007 FACH
 * 🇨🇳: licensed copy of GDF-002 as the Type 90, 150+ units with Skyguard FC radar
 * 🇨🇴: 75 GDF-005 units in reserve
 * 🇨🇾: 30 GDF-005 units used with Skyguard and Aspide SAM
 * 🇪🇨: 30 GDF-003 units
 * 🇪🇬: 72 Amoun units used with Skyguard and Sparrow SAM
 * 🇫🇮: 16 units. Known as 35 ITK 88
 * 🇩🇪: On the Flugabwehrkanonenpanzer Gepard (self-propelled anti-aircraft gun)
 * 44 GDF-002 units upgraded to GDF-006 AHEAD, used with upgraded Skyguard and Sparrow SAM
 * 🇮🇷: 92 GDF-002 units. Iran claims it is producing/refurbishing these guns. Used with Skyguard & Super Fledermaus FC radars.
 * 🇯🇵: some 70 GDF-001 units, used with updated Super Fledermaus FC radars. Made under a joint venture with Japan Steel Works for the 35mm gun and Mitsubishi Electric Corporation for the rest of the system 52 On the Type 87 (self-propelled anti-aircraft gun)
 * 🇰🇷: 36 GDF-003 units
 * 12 GDF-005 (Amoun) units, used with Skyguard and Sparrow SAM
 * 🇲🇾: 28 GDF-003 units
 * 🇳🇬: GDF-002 Type 90
 * 10 GDF-005 units AHEAD modified
 * 🇵🇰: estimated 200 GDF-005 units, 60 units AHEAD modified
 * 🇷🇴: 43 Flugabwehrkanonenpanzer Gepard systems and 72 GDF-003 units
 * 🇸🇦: 128 GDF-005 modified units. Used with Skyguard FC radars.
 * 34× GDF-001 + 24× GDF-002 units
 * some 100 GDF-002 + 48 modified GDF-005 units
 * 🇪🇸: 92 GDF-005 units, being upgraded to 007 standard. Skydor and Skyguard FC radars.
 * 45 GDF-007 modified units (from Total of 264 GDF-001/002 units)
 * 🇹🇼: 24 Skyguard “Sky Sentinel” Fire Control radars linked to some 50 GDF-003 35 mm twin guns. Upgraded to GDF-006 to fire AHEAD rounds since 2009.
 * 🇹🇷: some 120 GDF-002 units.118 upgraded to GDF-006 AHEAD.
 * 30 GDF-005 units
 * Total of 15 GDF-002 35mm twin guns were captured during the Falklands War along with 6 Skyguard and one Super Fledermaus FC Radars. One of the Skyguard radars was destroyed from a Shrike missile strike during the conflict. Currently four Skyguard fire control systems for these guns are being used to catch UK military aircraft exceeding flight restrictions over residential areas. GDF-002 guns now in storage and a few military museums in the U.K.
 * Total of 15 GDF-002 35mm twin guns were captured during the Falklands War along with 6 Skyguard and one Super Fledermaus FC Radars. One of the Skyguard radars was destroyed from a Shrike missile strike during the conflict. Currently four Skyguard fire control systems for these guns are being used to catch UK military aircraft exceeding flight restrictions over residential areas. GDF-002 guns now in storage and a few military museums in the U.K.