Close-in weapon system
A close-in weapon system (CIWS), often pronounced sea-whiz, is a naval shipboard point-defense weapon for detecting and destroying short range incoming anti-ship missiles and enemy aircraft which have penetrated the outer defenses.
Nearly all classes of modern warship are equipped with some kind of CIWS device.
Gun systems 
A gun based CIWS usually consists of a combination of radars, computers, and multiple barrel rapid-fire medium-calibre guns placed on a rotating gun mount. Examples of gun based CIWS products in operation are:
- Denel 35mm Dual Purpose Gun
- Goalkeeper CIWS
- Kashtan CIWS
- Meroka CIWS
- Myriad CIWS
- Oerlikon Millennium 35 mm Naval Revolver Gun System
- Phalanx CIWS
- Sea Zenith
- Type 730 CIWS
Limitations of gun systems 
- Short range: The maximum effective range of 20-mm gun systems is about 4500 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 to the ship's sensor or communication arrays, or to wound or even kill exposed personnel. This also makes the timeframe for interception relatively short; for supersonic missiles moving at 1500 m/s it is approximately one-third of a second.
- Limited kill probability: even if the missile is hit and damaged, this may not be enough to destroy it entirely or to alter its course enough to prevent the missile, or fragments from it, from hitting its intended target, particularly as the interception distance is short. This is especially true if the gun fires kinetic-energy-only projectiles.
- Guns can only fire at one target at a time; switching targets may take up to one second to re-train the gun.
- A gun must predict the target's course and aim at the predicted position. Modern anti-ship missiles make intentional erratic moves before impact, reducing the probability of being hit by unguided projectiles.
Comparison of some current CIWS 
|AK-630||Phalanx CIWS ||Goalkeeper CIWS||DARDO||Millennium|
|Weight||9,114 kg (20,090 lb)||6,200 kg (14,000 lb)||9,902 kg (21,830 lb)||5,500 kg (12,000 lb)||3,300 kg (7,300 lb)|
|Armament||30 mm (1.2 in) 6 barreled GSh-6-30 Gatling Gun||20 mm (0.79 in) 6 barreled M61 Vulcan Gatling Gun||30 mm (1.2 in) 7 barreled GAU-8 Gatling Gun||40 mm (1.6 in) 2 barreled Bofors 40 mm||35 mm (1.4 in) 1 barreled Oerlikon Millennium 35 mm Naval Revolver Gun System|
|Rate of Fire||5,000 rounds per minute||4,500 rounds per minute||4,200 rounds per minute||600/900 rounds per minute||200/1000 rounds per minute|
|(effective/ flat-trajectory) Range||4,000 m (13,000 ft)||3,600 m (11,800 ft)||2,000 m (6,600 ft)||4,000 m (13,000 ft)||3,500 m (11,500 ft)|
|Ammunition storage||2,000 rounds||1,550 rounds||1,190 rounds||736 rounds||252 rounds|
|Muzzle velocity||900 m (3,000 ft) per second||1,100 m (3,600 ft) per second||1,109 m (3,638 ft) per second||1,000 m (3,300 ft) per second||1,050 m (3,440 ft) per second / 1,175 m (3,855 ft) per second|
|Elevation||-12 to +88 degrees||-25 to +85 degrees||-25 to +85 degrees||-13 to +85 degrees||-15 to +85 degrees|
|Speed in Elevation||50 degrees per second||115 degrees per second||100 degrees per second||60 degrees per second||70 degrees per second|
|Traverse||360 degrees||-150 to +150 degrees||360 degrees||360 degrees||360 degrees|
|Speed in Traverse||70 degrees per second||115 degrees per second||100 degrees per second||90 degrees per second||120 degrees per second|
Missile systems 
|This section does not cite any references or sources. (March 2011)|
||The neutrality of this section is disputed. (March 2011)|
Missile systems do not have the same limitations as gun systems. Because of their greater range, a missile-CIWS can also be dual-used as a short-ranged area-defense anti-air weapon, eliminating the need for a second mount for this role.
After an inertial guidance phase, a CIWS missile relies on infra-red, passive radar/ESM or semi-active radar terminal guidance, or a combination of these. The ESM-mode is particularly 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.
- 9K33 Osa (SA-N-4 Gecko) missile, used by the Russian Navy is stored and fired from TELARs(Transporter erector launcher and radar) on various Russian ships.
- 9K331 (SA-N-9 Gauntlet) missile, used by the Russian Navy, it is stored and fired from Vertical launching systems of various ships. It along with the Tor missile system is the first air-defense system designed from ground up to intercept precision guided munitions like the AGM-86 ALCM
- 9M311 (SA-N-11 Grisom) missile, used by the Russian and Chinese navies as part of the Kashtan CIWS gun-missile system.
- Barak 1, an Israeli point defence missile system also used by Indian Navy.
- HQ-7 missile, a Chinese missile system, standard for all ships.
- RIM-116 Rolling Airframe Missile - jointly developed by the US and Germany it is used extensively on German warships and many American ones - SeaRam is a plan to mate the Phalanx sensor system with an 11 missile RAM launcher
- Sadral, using a version of the Mistral missile
- Sea-Sprint, using the ADATS missile
- Modernized 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.
- Evolved Sea Sparrow missile, used aboard all Sea Sparrow-capable warships, plus other warships of the Netherlands, Canadian, Spanish, Japanese, Turkish and Australian navies.
Land based CIWS 
On a smaller scale, active protection systems are used in some tanks, and several are in development. The Drozd system was deployed on Soviet Naval Infantry tanks in the early 1980s, but later replaced by explosive reactive armour. Other systems are available or under development are the Russian (Arena), Israeli (Trophy), American (Quick Kill) and the South African-Swedish (LEDS-150).
See also 
- Christian Wachsberger, Michael Lucas and Alexander Krstic (June 2004), Limitations of Guns as a Defence against Manoeuvring Air Weapons, DSTO Systems Sciences Laboratory, p. 36
- Dan Petty. "The US Navy - Fact File:". Navy.mil. Retrieved 2013-05-18.
- Tony DiGiulian. "Italy 40 mm/70 (1.57") Breda". Navweaps.com. Retrieved 2013-05-18.
- "Oerlikon Millennium 35 mm Naval Revolver Gun System - Wikipedia, the free encyclopedia". En.wikipedia.org. 2013-04-15. Retrieved 2013-05-18.
- "ЗЕНИТНЫЙ РАКЕТНЫЙ КОМПЛЕКС 9К330 "ТОР" (SA-15 Gauntlet)". Вестника ПВО (in Russian). 2007-08-21. Retrieved 2010-09-01.
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