ZSU - 23 - 4 Shilka The ZSU - 23 - 4 " Shilka " is a lightly armored , self - propelled , radar guided anti - aircraft weapon system ( SPAAG ) . ZSU stands for Zenitnaya Samokhodnaya Ustanovka ( Russian : Зенитная Самоходная Установка ) , meaning " anti - aircraft self - propelled mount " . The " 23 " signifies the bore diameter in millimeters . The " 4 " signifies the number of gun barrels . It is named after the Russian Shilka River . Polish soldiers nicknamed it " maszyna do szycia " ( sewing machine ) due to the sound of firing guns and because the similarity of name " Shilka " and Polish word " szyć " ( to sew ) . It is also referred to by its nickname of " Zeus " Description . 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 surpress 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 . Capabilities . 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 . 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 on board . 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 superelevation 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 . TheZSU - 23 - 4can be airlifted bytheAN - 22 or II - 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 . Limitations . 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