The' 9K505 ZSU-57-3M «Енисе́й» (tr. Yenisey) is one of the modern Soviet Union's principle short-range anti-aircraft platforms. It is a SPAD - a Self-Propelled Air Defense [System] - and is based upon the chassis of the ubiquitous T-110 Main Battle Tank. The name of the vehicle is derived from the configuration of its primary armament, with ZSU («ЗСУ») being an acronym for «Зенитная Самоходная Установка» [tr. Zenitnaya Samokhodnaya Ustanovka], or 'self-propelled anti-aircraft mount / installation', while -57- indicates the calibre of the cannon system (57mm), -3- represents the number of barrels and -M indicates an update (-Модернизированы, tr. '-Modernizirovany - Modernized). 9K505-1 is the GRU [Main Intelligence Directorate] Index designation (i.e. 'catalogue number') for the platform: 9K505 denoting a system designed for the 9S505 Missile with -1 appended to distinguish this particular vehicle from the similar ZSU-37-6, which also uses said missile and has the Index of 9K505-2. The Yenisey is the largest river system feeding into the Arctic Ocean.
Development
The ZSU-57-3 is part of a new generation of Soviet vehicles and self-propelled weapon systems designed around a relatively small set of modern, up-to-date chasses. Thus, it is but one of many derivatives based on the USSR's current Main Battle Tank, the T-110.
This desire to narrow the margin of different base vehicles / chasses in use for logistical purposes, and to extend the service life of the Union's entire vehicle fleet (rather than continuing the practice of incrimental upgrades to older systems), led to the development of the ZSU-57-3 and other designs like it - despite the assessment of the newer (but still relatively old) SPAAG systems in use at the time as "adequate".
Design
Like most of the USSR's late 20th century light AA vehicles, the Yenisey is a dual Autocannon/SAM platform. Unlike these older systems, however, its PRIMARY armament is considered to be its guns; its small missiles lack the electronic / network-warfare capabilities to effectively "run the gauntlet" (defeat the active/passive soft- and hardkill protection systems of modern aircraft) with a high rate of success.
Technically speaking, the main armament of the ZSU-57-3 is not a trio of 57mm autocannons, but three barrels linked around a single triple-feed self-actuating mechanism - a development of the Gast Principle first employed on the old dual Gsh-23L autocannons. In other words, the three chambers/barrels of the gun system are interlinked in such a way that the recoil from the discharge of the first barrel both loads as well as fires the second and so on in an theoretically-endless chain. Unlike older applications of the system, however, the ZSU-57-3 uses three barrels in a more complicated network and accomplishes much of its loading through an electric mechanism. The individual externally-visible guns - i.e. the barrels - are arranged in a triad pattern - that is, two on top and one on bottom.
Ammunition is fed to the triple-chamber/barrel arrangement through three independent belt feeds. The ribbons for the two lower cannons run around the perimeter of the turret while the upper is fed in an arc across the centerline of the roof, all of them connected to individual external ammunition canisters containing the rest of the length of a belt on an electrically-powered drum spool, giving the weapon system uninterrupted access to thousands of individual shells. Due to this arrangement, however, toggling between different types of ammunition is essentially impossible - dual-feed mechanisms for each of the chambers were tested in the initial design phase in an attempt to help remedy this problem, but this was judged too complicated. As such, the Yenisey almost universally fires general purpose high-explosive fragmentary munitions.
Where time / situation warrants, particularly at night, the standard rocket-assisted propulsion shells (which, like most Soviet ammunition, use an integral rocket motor to provide additional velocity development and stability for the round once it leaves the barrel) can be replaced with 'low-signature rounds' using a less effective but much less visible combustionless gas charge (making the weapons' fire much less visible in terms of both eyesight as well as sensory equipment). Also like most modern Soviet guns / cannons, it uses the ETC (Electro-Thermal Chemical) propellants incorporating small electrically-triggered plasma charges to combust the projectile propellants at a precisely-controlled, predictable rate. This improves accuracy and muzzle-velocity, as well as general performance (including more predictable ballistic trajectories less susceptible to external conditions), by maximizing the 'power per unit' during propellant combustion. The rounds for the Yenisey system have their own limited in-flight course correction capability and will automatically adhere to a set 'straight line' trajectory for as long as their rocket motors last (i.e. they self-compensate for muzzle drop, wind interference, barrel wear, etc). They can be slaved to guidance lasers built ino each gun barrel for actual in flight course modification, but this system is not always used as it can cause the rounds to under-shoot their intended target if the tracking information is not up-to-date enough.
The ZSU-57-3's secondary armament, from which its 9K505 sub-designation stims, is six MCA (magnetic coil assisted), cold-launch tubes for 9S505 missiles. These are small, high-speed, Scramjet-powered SAMs with limited onboard computing / networking power which, due to these latter characteristics, must be used with careful discernment to successfully hit a modern aircraft. As such, they are used sparingly, since they are incapable of receiving full in-flight target information / trajectory updates from more powerful computing systems than those onboard their Yenisey launch platforms. The ZSU-57-3 vehicle generally carries one spare missile for each of its launchers, although it has a capacity to hold more, because the launch-assistance coils in the tubes are worn down to the point of degraded effectiveness after two uses (owing to their short length). The tube liners containing the coils must therefore, ideally, be replaced once the initial missile load is exhausted, although if necessary they can be fired safely at least twice more. Each missile comes pre-packaged in a sabot with the carbon-nanotube grid battery holding the necessary charge for the magnetic launcher which propels it.
Other / Contemporary Soviet Short-range SPAD Systems
- '9K505-2 ZSU-37-6M Lena' - a similar system, also built on the T-110 base, which is nearly identical apart from having a gun armament of two triple 37mm cannon systems. This air defense platform has more of a point-defense role, and is more optimized for engaging incoming hostile munitions or helicopters / low-flying VTOL aircraft, but is used in the anti-aircraft role alongside the ZSU-57-3 as well. The two systems generally operate in concert.
- 'ZSU-85-2 Amur' - a newer T-110-based platform which is a pure SPAAG (Self-Propelled Anti-Aircraft Gun) system, lacking secondary SAM armament. The ZSU-85-2 packs dual-linked, rapid-fire 85mm cannons using essentially the same system as the other ZSU- platforms on a larger scale. It is ideal for firing on fixed-wing aircraft, other airborne targets out at longer ranges as well as clusters of incoming munitions.