Sea Zenith Ciws

have been developed to circumvent this problem.

Some of the guns used in radar-directed systems are also available in locally controlled mountings and have therefore already been described. The main exceptions are at the extremes: larger-calibre guns which are always radar-directed, and very fast-firing cannon used in the specialised CIWS anti-missile mountings.

Dealing with the weapons in calibre order means starting with the CIWS. The American Phalanx was the first in the field in the late 1970s and is now in service with many navies including the RN. The gun used is the six-barrel 20mm M-61 Vulcan cannon firing 20 X 102 ammunition and originally designed for equipping fighter aircraft. In that form, it is capable of firing at 6,000 rpm, although it is derated to between 3,000 and 4,500 rpm (depending on the version) for the Phalanx application.

In common with most other CIWS, Phalanx does not fire the usual full-calibre explosive shells but APDS rounds instead: solid, high-velocity, depleted-uranium projectiles of 12.5mm calibre contained in a light sleeve which falls away as it leaves the muzzle.

The reason for this choice of projectile, which is actually less effective than HE shells against aircraft, is that while larger guns and AA missiles can knock down anti-ship missiles at a distance by blowing away their wings and controls with prox-imity-fuzed explosive warheads, once the missiles get within 600-700m of a ship, their ballistic momentum is likely to carry them to the target even if they are damaged. Phalanx bullets are therefore intended to penetrate and explode the missile s warhead. Even so, a typical 200kg RDX warhead has to be exploded at least 150m from the ship to avoid blast damage.

The Phalanx mounting weighs about 6,000kg and contains ammunition for nearly twenty seconds' firing; this is enough for several engagements as the gun fires in short bursts. The maximum range is about 1.5km. A significant advantage of the mount is that it requires no deck penetration and thus can be bolted in any convenient location, top-weight considerations permitting.

Another mounting which uses a 20mm rotary cannon is the Sea Vulcan 20. This is very different from Phalanx as it is intended for small craft and does not use closed-loop guidance technology. The gun is a three-barrel M197 version (using the same 20 X 102 ammunition) capable of up to 1,500 rpm and the mounting is very small, weighing only 318kg when empty.

An alternative approach to obtaining a high rate of fire is used by the Spanish Meroka. This

M197 Machine Gun MountSea Zenith Ciws

Oerlikon Sea Zenith CIWS with four 25 mm KBB cannon (Courtesy: Oerlikon/lan Hogg)

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