ZRK-23-4 / ZSU-23-4 Shilka 23MM Antiaircraft Gun
The Shilka ZSU-23-4 [ZSU = Zenitnaya Samokhodnaya Ustanovka - Anti-aircraft Self-Propelled Gun] is a Self-Propelled Anti-Aircraft Gun (SPAAG) featuring a prominent radar dish that can be folded down mounted on a modified PT-76 chassis. ZSU 23-4 Shilka, is capable of acquiring, tracking and engaging low-flying aircraft (as well as mobile ground targets while either in place or on the move). Employed in pairs 200 meters apart, 400 meters behind battalion leading elements, it is commonly used to suppress ATGM launch sites, such as TOW vehicles. The armament consists of four 23mm cannon with a maximum slant range of 3,000 meters. Ammunition is normally loaded with a ratio of three HE rounds to one AP round. Resupply vehicles carry an estimated additional 3,000 rounds for each of the four ZSUs in a typical battery. Recent (October 1997) information details ZSU-23-4 updates/modernization being offered by the Ukrainians that include: a new radar system replacing the GUN DISH radar, plus a sensor pod believed to include day/night camera, and a laser rangefinder; and mounted above radar/sensor pod is a layer of six fire-and-forget SAMs, believed to be Russian SA-18/GROUSE.
The ZSU-23-4 is a fully integrated, self-propelled antiaircraft system with four liquid-cooled 23-mm automatic cannons mounted on the front of a large, flat, armored turret. The chassis has many components borrowed from other Soviet armored vehicles, and the suspension system resembles that of the PT-76 and ASU 85 (six road wheels and no track support rollers). The driver sits in the left front of the hull, and the rest of the crew (commander, gunner, and radar operator) are located in the turret. The GUN DISH fire control radar mounted on the rear of the turret can be folded down during travel.
A number of different ZSU-23-4 models have been produced. These are primarily distinguishable externally by the types of stowage boxes on the turret and minor modifications in the mounting of the guns.
Inherent weaknesses like the limited effective firing range against aerial targets, insufficient ammunition power and the radar’s shortcomings were eliminated in three upgrades over half a century. By 2014 the Shilka was still in service with 39 countries. It was also used in the 1980s to develop the Tunguska air defense system, the forerunner of the contemporary Pantsir-S1, which is armed with short- to medium-range surface-to-air missiles and an anti-aircraft artillery system.
A platoon of four ZSU-23-4s is assigned, along with four SA-9/GASKIN SAM systems, to the antiaircraft battery of motorized rifle and tank regiments to cover the deadspace of the SA-6/GAINFUL in the division air defense umbrella. Two ZSU-23-4s usually will be in support of each of the two first-echelon battalions, each weapon normally separated by 200 meters, typically traveling 400 meters behind the battalion's leading elements.
The ZSU-23-4 is not amphibious, but has a fording capability of just over one meter. During river assault operations, the ZSU-23-4s would be ferried to the far bank immediately after the leading companies.
Firing 4,000 rounds a minute, the Shilka can hit aerial targets flying at 450 meters per second at an angled range of 2,500 meters or 2,000 meters vertically. Its guns can be sighted visually or by its radar, which automatically tracks targets and feeds data to its computer to generate pre-emptive firing coordinates. The tilt angle of the gun is also automatically set to compensate for any pitching of the vehicle when in motion.
The ZSU-23-4 has the capability to both acquire and track low-flying aircraft targets, with an effective AA range of 2,500 meters. It also is capable of firing on the move because of its integrated radar/gun stabilization system. The high frequency operation of the GUN DISH radar emits a very narrow beam that provides for excellent aircraft tracking while being difficult to detect or evade. However, such a frequency also dictates a limited range, which can be compensated for by linking the system to other long-range acquisition radar in the area. The ZSU-23-4 also can be used against lightly armored ground vehicles.
The four guns are water cooled and have a cyclic rate of fire of 800 to 1,000 rounds per minute each. However, the guns are normally fired in bursts (2-3 rounds per barrel) to reduce ammunition expenditure and prolong barrel life. Each ZSU-23-4 carries about 2,000 rounds onboard. Supply trucks, which follow the ZSUs at a distance of 1.5 to 2.5 km, carry an estimated additional 3,000 rounds for each of the four ZSUs. Electronic target acquisition, tracking, and ranging are automated, and an onboard computer determines super elevation and azimuth lead. Conventional optical sights also are available. Two types of ammunition normally are mixed at a ratio of three Frag-HE-T rounds per one API-T round. An HEI-T round also may be fired.
The ZSU-23-4 can be airlifted by the AN-22 or IL-76. The crew of the ZSU-23-4 is afforded a degree of protection by the thin armor (maximum thickness 9.4 mm in the hull, 8.9 in the turret). Collective NBC protection is provided by a radiation detection and warning system and an air filtration and overpressure system.
Heavy machine gun fire can penetrate the hull and turret. Tread and road wheels are vulnerable to artillery fire. HE fragmentation can penetrate the armor, destroy the radar dish, or rupture the liquid coolant sleeves of the 23-mm cannons. The system also is vulnerable to ECM.
Anti-aircraft weapons available in the 1950s were not guaranteed to hit fast-flying targets, and rather laid down a screen of fire to ward off enemy planes from ground assets. Land cruisers of the Revolution: Meanwhile, building on German know-how captured in 1945, both the United States and the Soviet Union were busy developing the first anti-aircraft missiles. Designed to hit targets at medium and high altitudes, these still allowed enemy aircraft to fly below 300 meters with relative impunity. A new mobile artillery system capable of firing on the move was needed. The U.S. military was still using the M42A1 Duster, a tank-based anti-aircraft system with a twin-barrelled 40 mm gun. Work was also underway on the 20 mm M163 Vulcan system, which would be mounted on an armored personnel carrier.
The Soviet Union also had two systems under simultaneous development, a 23 mm four-barrelled model and a 37 mm twin-barrelled rival, named the Shilka and Yenisei after Siberian rivers. The Shilka ZRK-23-4 won the race but still had some drawbacks. The caliber of ammunition it used was rare in the Soviet forces, and the 28-ton mass of the combined gun and carrier meant it had to be used with tank units. The deciding factor in its favor was its efficiency against low-altitude and close-range targets. The ZRK-23-4 went into service in 1962, five years before the U.S. Vulcan, and was a “real revolution", retired Soviet Army colonel Anatoly Dyakov wrote in his memoirs: “While today’s officers take such autonomous units for granted, it was the pinnacle of engineering design in the 1960s."
While well shielded from interference, the radar has a low range of only 6-12 miles, depending on weather conditions. This shortcoming was revealed during the Arab-Israeli wars of the 1960s and 1973. But although under-trained Syrian crews often preferred to sight the weapon visually, the Shilka is still credited with downing 16 of 117 aircraft shot down by Syrian air defense forces in 1973-1974.
In 1975, the weapon saw action in Angola, when a handful of Cubans used it to halt the combined advance of fighters of FLEC (Front for the Liberation of the Enclave of Cabinda) and regular Zaire Army units. After mining the roadside, they opened fire from pre-prepared positions and wiped out an entire enemy convoy.
The Soviets used a similar weapon to deal with ambushes in Afghanistan. Unlike tank and armored car guns, the Shilka’s barrels could be elevated vertically to target mujahedin fighters on cliff tops. This yielded a special “Afghan variant" of the ZSU-23-4 that had no radar equipment so as to increase ammunition storage and firing capacity to 4000 rounds per minute.
Despite already being obsolete by 1990, the Shilka caused the loss of Western coalition aircraft during the First Gulf War by forcing pilots to act cautiously at low altitudes and make mistakes. But it did not only make its mark against airborne targets. The sheer intensity of fire produced by the towed version of the gun was valued by guerrilla forces around the world.
The Shilka also fought with devastating effect in the wars in Chechnya. The former head of the North Caucasus military district, Lieutenant-General Vladimir Potapov, noted its high efficiency against enemy strongholds and firing points. Perfected in street fighting, the tactic of using the Shilka when facing strong enemy resistance is to drive the vehicle out from behind cover, give long bursts of fire and immediately pull back," Potapov wrote in an assessment of combat results.
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