Defence power

developments of the decade

Tim Ripley explains why top-of-the-range ship defence systems are essential to navies worldwide.

On February 25, 1991, British Type 42 destroyer HMS Gloucester detected two Chinese-made Silkworm anti-ship missiles being launched from Iraqi-occupied Kuwait. Their target was the American battleship USS Missouri that was bombarding Iraqi positions during the first hours of the coalition land offensive to liberate Kuwait.

Within two minutes the Gloucester detected the launch, identified it as hostile and launched a Sea Dart missile to successfully intercept the Iraqi Silkworm that exploded above the British warship. This engagement was a text book example of successful ship defence and con-trasted with the British experience nine years before during the Falklands War when French- made Exocet missiles put three British ships out of action and severely hampered the Royal Navy's operations to recapture the Argentine- occupied islands.

Tests have demonstrated the vulnerability of modern weapon systems

The Gloucester incident identified all the main elements of a successful ship defence engage-ment: surveillance, identification, authorisation to engage and final engagement. The capability to carry out these functions applies to the three main naval threats; air, surface and sub-surface.

The Aerospatiale Aster 15 being tested for inner zone air defence

Air defence

Since World War Two, navies have taken the threat of air attack very seriously and devoted considerable efforts to protecting their ships. Radar is the main detection system used by warships to provide early warning of air attack, although some navies are assessing the potential of thermal-imaging systems to defeat enemy electronic counter measures. However, the success of a ship defence engagement largely is dependent on how well its combat informa-tion centre (CIC) is able to assess, analyse and respond to threats. Given the supersonic speed of modern attack aircraft and missiles with speeds up to 800 metres a second, reaction times must be measured in seconds rather than minutes. CICs have to respond to threats, select and launch weapons and differentiate between friendly and hostile contacts. There is also a requirement to co-ordinate with nearby friendly forces so the ship with the optimum solution engages the threat.

Warships bristle with electronic sensors and radars that feed information into ships' defensive systems

NATO and allied navies place great stress on compatibility of CIC systems to allow air defence data to flow freely between surface units and alliance aircraft. The primary NATO data links, Link 11 and Link 16 JTIDS (joint tactical infor-mation distribution systems), are well proven and widely installed on western warships. These systems allow for the creation of what is called a recognised air picture in a theatre of opera-tion, so every air and surface unit has full situ-ational awareness about what is happening in the air defence battle. The recognised air picture also can be used to pass engagement orders to individual ships.

The trusty old Browning .50 cal machine guns are used on US Navy sides for close defence against air and surface threats

While CIC systems are the brain of a ship's defensive systems, its weapon systems have to be equally advanced to stand a chance of defeating the current generation of smart anti-ship missiles. Passive defensive systems are designed to defeat the sensors that guide enemy missiles and most modern warships are fitted with radar jammers to interfere with enemy missiles' radar guidance systems, radio jammers to block signals guiding missiles and decoys to spoof enemy missiles into attacking the wrong target. Decoys come in three main types. Chaff consists of small strips of aluminium that is fired from rockets and creates a false radar image. Active decoys are towed behind ships or heli-copters and consist of reflective panels that magnify radar signals. Thermal decoys are flares that are fired to provide alternative heat sources for infra-red guided missiles.

Active weapon systems, guns and missiles are deployed in layers to provide added security in case the first line of defence does not succeed in neutralising the threat. Missiles provide the outer layer of defence and inner layers are pro-vided by a combination of guns and missiles. Often long-range or area defence is carried out by specialist anti-air warfare destroyers or cruisers such as the British Type 42s or the American Aegis that fire the British Aerospace Sea Dart and the General Dynamics Standard Two (SM-2) respectively. The latest Block IV versions of the Standard are claimed to be able to hit targets at 400kms (SM-2ERs currently in service have a 137km-range) and the Sea Dart has a range up to 40km. The French-developed Aero-spatiale Aster-15 missile has been selected to be the principal anti-aircraft missile system (PAAMS) for the new tri-national European Horizon common new generation frigate.

Missiles provide most of the next layer of defence, out to 15km or so, and include the agile British Aerospace Sea Wolf, Raytheon RIM-7 Sea Sparrow and Aerospatiale Crotale. These use a variety of sensors and guidance systems, including radar, electro-optical and infra-red. Originally air defence missiles were fired from on-deck launchers and re-loaded by complicated mechanical systems from internal magazines. This system proved unwieldy in combat scenarios requiring rapid re-loading so many navies are opting for vertical launch sys-tems that have fewer moving parts.

Helicopters such as the Sikorsky SH-60 Sea Hawk extend the range of a ship's surface and sub-surface defence

Point or close-in defence primarily is the pre-serve of gun systems that aim to take down targets up to 5km from the target ship. Highly automated and radar-guided close-in weapon systems (CIWS) such as the American Phalanx and Dutch Signaal Goalkeeper use 30mm rotary gatling guns that are designed to fill the air in front of in-coming missiles or aircraft with a wall of lead. The Swiss Contraves company has been leading the way in the development of anti-aircraft systems that use radar fused shells that explode in the path of oncoming threats and spray them with flacettes. As a last resort the majority of warships have manually operated machine guns and 20mm light anti-aircraft cannon on their decks.

Sub-surface threats

Enemy submarines pose a major threat to sur-face ships and considerable effort is spent pro-viding warships with effective defence against them. The most significant advance in anti-submarine warfare (ASW) over the past 20 years has been the widespread fielding of tower sonar arrays that allow underwater sound to be picked up at unprecedented ranges. On-board sonar sensors suffer greatly from noise interference caused by ships. As detection is possible at long ranges, ships can employ their own ASW weapon systems to better effect. On-board ASW weapons consist primarily of homing torpedoes such as the US Mk46 fired from launch tubes or Asroc missiles. Most navies also field depth charges that are dropped from ships directly above a submarine contact.

Raytheon Sea Sparrow missiles are used by NATO navies for inner zone air defence

To extend the reach of ASW coverage, almost all frigates boast a light helicopter of the West-land Lynx or Sikorsky Sea Hawk class, armed with ASW homing torpedoes. The addition of dunking sonar significantly increases the ability of helicopters to detect and launch weapons against submarines.

To provide passive defence against in-bound enemy-homing torpedoes many warships now have been fitted with acoustic counter measures that provide alternative sound sources to mimic the signature of the target. These either can be towed or fired from dispensers.

Surface defence

The fielding of long-range surface-to-surface missiles such as the Exocet and Harpoon in the 1970s led many navies to consider that the gun was redundant as a defensive weapon against surface threats.

In the 1990s naval guns have been making something of a come-back as defensive systems, not just against air threats. This is for a number of reasons. First, politically sensitive crisis man-agement scenarios often are conducted under tight rules of engagement that require visual identification. Missiles, particularly radar-guided weapons, tend to be indiscriminate once launched, making them uneffective weapons in such circumstances. The increasing number of littoral campaigns in confined coastal waters have changed the nature of many naval threats. In such circumstances small craft, fast patrol boats and rigid raiders are able to sneak past radar cover and close to short range (under 5km) before being detected. The most effective way to deal with this type of threat is air-burst high-explosive shells that kill their crews and fill the boat with shrapnel.

The US Navy's Phalanx is designed to be a ship's last line of defence against aircraft and missiles

Guns now are beginning to be more cost effec-tive than missiles. They are re-usable and the relatively low cost of rounds means it is possible to afford to spend money on training rounds for crews, whereas missile crews often get to fire only one missile every year in most western navies. In less-developed navies, crews never get the chance to fire a single round.

The economic case for guns versus missiles also has been advanced by the large surplus of 155mm artillery ammunition available in the arsenals of western ground forces. By adopting common calibre with ground forces, navies can achieve even greater savings.

The USS Stark's defensive systems in 1987 were not capable of detecting and defeating Iraqi Exocet anti-ship missiles

New technology also has made guns more effective than in the past, giving them longer range and throw weight. The so-called thermal gun that uses an electrical charge rather than conventional means to ignite shells offers oppor-tunities as does the use of liquid propellant.

Ship defence systems are essential features of any modern warship, in spite of their expensive installation. The high cost of hulls means they are prized equipment that few navies can afford to lose or damage. Navies can no longer afford not to install top-of-the-range defensive systems.