The ZSU-23-4 "Shilka" is a lightly armored Soviet self-propelled, radar guided anti-aircraft weapon system (SPAAG). The acronym "ZSU" stands for Zenitnaya Samokhodnaya Ustanovka, meaning "anti-aircraft self-propelled system"; the "23" signifies the bore diameter in millimeters; the "4" signifies the number of gun barrels. It is named after the Shilka River in Russia. Afghan soldiers nicknamed it the "sewing machine" due to the sound of firing guns. It is also referred to by its nickname of "Zeus", derived from the Russian acronym.
The radar-guided ZSU-23-4 "Shilka" SPAAG, with its four 23 mm autocannons, was a revolutionary SPAAG, proving to be an extremely effective weapon against enemy attack aircraft and helicopters under every weather and light condition. The ZSU-23-4 has a very high density, rate and accuracy of fire, as well as the capability for each of the four autocannons to fire its own type of projectile from separate belts. While it is technically possible that each cannon shoots different type of ammunition, there were two types commonly used in late 1970s: OFZT incendiary fragmentation and BZT armour-piercing tracer, which were to be loaded in 3:1 ratio-three OFZT, then one BZT, every 10th BZT round equipped with so-called "copper remover" and marked. Operators were strongly discouraged from shooting from a single barrel. The appearance of the "Shilka" caused significant changes in NATO tactics in aircraft use at low altitude over the battlefield. Despite its present obsolescence as a modern short-range anti-aircraft weapon, the ZSU-23-4 is still deadly for enemy light armoured vehicles, infantry and firing points as an infantry-support vehicle. With its high rate of accurate fire, the ZSU-23-4 can even neutralize tanks by destroying their gun sights, radio antennas, or other vulnerable parts. ZSU-23-4s, especially late models, have excellent performance and good systems reliability.
Based on the GM-575 tracked vehicle chassis, which used components from the PT-76 light amphibious tank, the ZSU-23-4 mounts an armored turret holding four liquid-cooled 23 mm (0.9") 2A7 autocannons linked to an RPK-2 "Tobol" radar (NATO designator: "Gun Dish"). The vehicle weighs 19 tonnes (late modifications up to 21 tonnes), has a movement range of 450 km (280 mi) and a top speed of 50 km/h (31 mph). Additional firepower of late modifications can be supplied by a roof-mounted pod of six short-range SA-18 SAMs, or side-mounted SA-16s. The crew numbers four: driver, commander, gunner and radar operator. The driver's compartment is located in the nose part of the vehicle. The fighting compartment is in the center, and the engine compartment is in the rear part of the vehicle.