Radardirected antiaircraft

and anti-missile guns

The problem of hitting fast-moving aerial

Targets is so difficult for manually aimed weapons that this task is now given to missile systems or remotely controlled guns which are automatically directed by radar. All the gunner has to do is specify the target and command the system to open fire. These are generally known as close-in weapon systems (CIWS). Many of these mountings also carry electro-optical back-up sights to provide an alternative control mode.

Sea-skimming anti-ship missiles are even harder targets than aircraft and there is usually very little warning of attack. Systems to combat them are therefore normally fitted with fire controls which automatically detect and engage incoming missiles without the intervention of a gunner, who merely has to make sure that the system is switched on.

There are two different philosophies in the design of anti-missile gun systems. One relies on large-calibre cannon (35mm and upwards) firing explosive projectiles which are detonated close to the target by a proximity fuze (or in the case of the 35mm Oerlikon AHEAD system, by a time fuze). The other fires intense bursts of small-calibre solid projectiles from fast-firing cannon of 20-30mm which are intended to score direct hits on the target, penetrating and detonating the warhead.

There is much debate about the merits of each approach. Large-calibre cannon systems permit engagement at a longer range and are inherently more versatile, being well suited to anti-aircraft and possibly anti-surface vessel applications. On the other hand the most advanced small-calibre systems, such as Phalanx and Goalkeeper, are very accurate because they have a 'closed loop* fire control system which monitors via the on-mount radar the trajectory of the gun's projectiles as they speed towards the target, calculates the probability of hitting and adjusts the aim accordingly.

There is considerable overlap between anti-aircraft and anti-missile gun systems. Many of the former, even at gun calibres as large as 100mm, are claimed to be effective in the anti-missile role when used with an appropriate fire control system, and the latter are all capable of acting in the anti-aircraft role, although in some cases only at short range.

Large-calibre weapons usually have their radar directors sited many metres away from the gun mountings, which can cause accuracy problems if there is the slightest flexing of the ships hull in rough seas. A further problem with very large-calibre AA guns in the anti-missile role is that their proximity fuzes are usually set to detonate the shell some distance from the target because of the large lethal radius of the shell. However, many modern anti-ship missiles fly so low that large shells might be detonated by the proximity of the sea before they reach the target. Advanced fuzing systems

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