Close-in weapon system
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Image:Close-In Weapon System.jpg
A Close-in weapon system (CIWS) is a naval shipboard weapon system for detecting and destroying incoming anti-ship missiles and enemy aircraft at short range (the threat(s) having penetrated the ship's available outer defences). Typically, the acronym is pronounced "Sea-whiz."
A CIWS usually consists of a combination of radars, computers, and multiple rapid-fire medium calibre guns placed on a rotating gun mount. One of the more well-known CIWS products in operation is the US Navy's Phalanx system. Another well-known CIWS is the Dutch-built Goalkeeper. Several others, such as the Turkish Sea Zenith, the Spanish MEROKA, the Russian AK-630 or Kashtan, the Italian DARDO or Myriad, and the Chinese Type 730.
Nearly all classes of modern warship are equipped with some kind of CIWS system. Smaller CIWS-like defenses are currently being developed for main battle tanks in the USA, China and Russia ("Drozd" and "Arena" grenade launchers in the case of Russia).
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How does it work?
The CIWS was made as a last line of defence, so its mission is not to shoot all missiles down. Instead it shoots the warhead of the missile so that it will not cause serious damage to the ship. If it fails at that it will shoot from front to back, putting holes in the missile, attempting to either throw it off course or prematurely detonate it.
Missile systems
The current trend in CIWS is to use missile systems instead of guns, because guns have certain limitations:
- Short range: The maximum effective range of 30 mm gun systems is about 2000 m; systems with lighter projectiles have even shorter range. The expected real-world kill-distance of an incoming anti-ship missile is about 500 m or less, still close enough to possibly cause damage on the ship's sensor or communication arrays. Also the timeframe for interception is relatively short; for supersonic missiles moving at 1500m/s it is approximately one third of a second.
- Limited kill probability: Even if the missile is hit and damaged, it may not be enough to destroy it or change its course enough, to prevent it or fragments of it from hitting its intended target (short interception distance, see above). This is especially true if the gun fires kinetic-energy-only projectiles (e.g. Phalanx with DU-rounds).
- They are only able to engage one target at a time and switching targets needs up to one second for training the gun. A coordinated salvo of missiles can easily overwhelm a gun-based CIWS.
- For a gun hitting a target travelling at high speed it has to predict its course and point ahead of it since mid-course corrections of projectiles are not possible. Modern anti-ship missiles make erratic moves before impact, reducing the probability of being hit.
Because of their greater range, a missile-CIWS can also be dual-used as a short-ranged area-defence anti-air weapon, eliminating the need of a second mount for this role. Image:RIM-116 Rolling Airframe Missile Launcher 1.jpg After an inertial guidance phase CIWS missile rely on infra-red, passive radar/ESM or semi-active radar terminal guidance or a combination of these. The ESM-mode is particular useful since most long-range anti-ship missiles use radar to home in on their targets. Some systems allow the launch platform to send course-correction commands to the missile in the inertial guidance phase.
Examples include:
- Crotale-NG
- RAM - Sea-RAM is a version planned as a direct replacement for Phalanx, using Phalanx' sensors and mounts
- Sadral, using a version of the Mistral missile
- Sea-Sprint, using the ADATS missile
- modern Sea Wolf
- Sea Sparrow Block 1, Missile used by the Nimitz class carriers, and other USN ships, as a short to medium range anti-aircraft weapon.
CIWS trivia
- Because of the inefficiency and bulkiness of the original CIWS units, the acronym received the derisive backronym of "Christ! It Won't Shoot!" (the word "Christ" may be exchanged with "Captain" for a milder version).
- The original CIWS units are sometimes referred to as "R2-D2s" due to the cylindrical radome's physical resemblance to the Star Wars character.
- The movie version of Tom Clancy's The Sum of All Fears features a brief scene where Russian fighters fire missiles at a US aircraft carrier, whose CIWSs open fire to try and stop the incoming missiles. One or two missiles are destroyed but the rest hit and damage the carrier.
- Several of the warships in Mobile Suit Gundam SEED feature automatic CIWS systems along their hull.