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By Martin Edmonds, Director CDISS, |
Anti-submarine warfare: |
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| During the cold war – the 40-year period from 1949 until 1989 – the submarine presented the most formidable threat to the security of both east and west. This stemmed from a number of well-founded reasons: historically, the successes of German submarines during 1917 almost brought the allied cause to an end. Only by adopting the convoy system were they able to be contained.
This experience was almost repeated during World War II when in 1942 and 1943 Kriegsmarine U-boats inflicted unacceptable losses on the logistics lifeline between the US and Britain. The convoy system provided only part of the solution because wolf-pack tactics of German submarine commanders could penetrate the convoy’s defensive screen. It was maritime patrol aircraft (MPA) that effectively neutralised the underwater threat. Nevertheless the submarine posed the threat of cutting off the reinforcement of Europe from the US as their performance improved. After the war, the threat of separating Europe from the US continued, culminating in the large, fast and silent nuclear-powered SSN.
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| Operationally, the modern SSN had a reach limited only by the endurance and logistic supply of the crews. This meant submarines of both sides in the cold war could remain submerged for months and reach territorial waters of the other side with impunity. The chronicles of the period reveal that this was frequently what happened, for clandestine and covert intelligence operations as well as for normal, defensive patrol purposes.
As defence technology developed rapidly during the 1950s and 60s, so did the vulnerability of both side’s nuclear deterrent. The nuclear submarine, equipped with underwater-launched ICBMs, offered the best solution. Although land and air-launched nuclear missiles were retained, the submarine-launched ballistic missile system (SLBM) remained the deterrent system of choice. In Britain’s case, it became the only deterrent system when the Polaris system became operational, replacing the Vulcan strategic bomber. The former Soviet Union introduced its first operational SLBMs in the early 1970s after an accelerated development programme following the Cuban missile crisis. Such was the significance of the submarine threat to both sides that anti-submarine warfare (ASW) became a top research and development priority. But it was also one of the main targets for espionage. Significant progress in underwater sensors, data processing, torpedo and intelligence technologies was made throughout the cold war. By the late 1980s, one US Navy captain even concluded that the death-knell had been tolled for the submarine. In some measure he was right, so long as ASW was confined to the cold, blue waters of the Atlantic and Pacific Oceans. Progress in ASW, however, was paralleled in the development of nuclear-powered and conventional submarines. Both were capable of long periods submerged and both became more difficult to detect as they incorporated stealth characteristics and reduced their noise signature. The requirement of diesel electric-powered submarines (SSK) to snorkel and recharge their batteries at frequent intervals was greatly reduced in the late 1980s after the introduction of air independent propulsion (AIP) systems. The end of the cold war meant that major powers no longer perceived the submarine threat in the same way and reduced their submarine and anti-submarine capabilities. In Britain and the US, the decision was taken to dispense entirely with SSKs and to concentrate on fewer, more capable, SSNs. France, Italy, Spain, Germany, Holland and Sweden remained committed to the SSK. But the Russian Federation, with an ailing economy, elected to concentrate on submarine development, believing it to be the guarantor of Russian safety and security. The western states also cut back on maritime patrol aircraft and so reduced the experience and competence of ASW personnel in what is acknowledged as one of the most demanding areas of military technology. While western states were recasting their defence policies and entertaining such concepts as preventative diplomacy, an increasing number of littoral states throughout the world began to modernise their naval surface fleets, acquiring more modern SSK patrol submarines, such as the Russian kilo class submarine, the German Blohm and Voss Type 209 SSK and the Swedish Sjoorman-class boats. Both France and Spain have been active in the conventional submarine market with their joint Scorpene class of SSK. Indeed, there has been a proliferation of advanced conventional submarines over the past ten years at a time when the art and science of ASW has been in steep decline. Those countries that have made recent submarine acquisitions have looked to the SSK to provide the defence and protection of their territorial waters. The irony here is that it is precisely in these regions where the conventional submarine has not figured prominently in the past. Now these are the regions where western members of the Security Council focus their future defence policies, and where they anticipate performing an interventionary role to stop or help prevent local conflicts escalating. This new focus of UK defence policy was incorporated in the strategic defence review of 1998 and mirrors the US 1997 quadrennial defence review. There are now 43 states in the world operating conventional submarines. Only China, the US, Russia, France and the UK deploy SSNs. In the 1980s, Brazil attempted to do so but had to abandon the scheme for financial and technical reasons. The projection is that the number of states deploying SSKs will increase and those that have them will modernise existing submarines and expand their fleets. Submarine detection Joint combined interventionary forces deployed by major western navies in unstable regions are likely to encounter hostile SSKs operating in coastal or brown and green, waters. This is significant because these environments are where cold-war ASW technologies, developed for operating in the cold, deep-blue oceanic waters, are less effective. Submarine detection in green and brown coastal waters is very difficult for many reasons. First, in green waters, defined as waters of the continental shelf, there is a mixture of drifting water bodies of different temperatures, salinities and velocities that with shallow and turbulent conditions, limit sonar range. To add to these difficulties there are shoals of fish, rocky outcrops and wrecks that generate false contacts. Low-frequency sonars lack the precision needed, and active sonars give any stealthy SSK advance warning. The only development that offers promise of detecting the SSK in these waters is the reliable acoustic path (RAP) system that uses a vertical sonar beam that is less affected by differences in thermal layers or salinity. US experiments have involved a lattice of linked RAP sonars in a fixed distributive system that could detect an SSK passing over it. But these are limited in their coverage. Coastal waters from the shore out to 25 miles, or brown water conditions, are even more difficult. Currents, thermal disturbances and winds cause active sonar transmissions to deflect downward, reducing effectiveness to a few hundred metres. Further problems that make SSK detection difficult include industrial debris found off-shore, and muddy conditions that degrade acoustic signals and make visual sighting impossible. Outflows of cold freshwater from rivers flowing under sea water warmed by the sun create thermal layers that trap sonar signals in sound channels, or ducts. Effective ASW solutions An SSK, operating in these conditions, carefully located near wrecks or rocky pinnacles and kept stationary or moving at less than five knots, is almost impossible to detect by acoustic means. And because coastal waters probably would be within range of shore-based anti-shipping missiles or land-based aircraft, any sea-based ASW operation other than by submarine, could be vulnerable. The high-frequency dipping sonar operated from ASW helicopters is said to give submariners their biggest headaches and may prove to be the most effective solution. There is a range of alternative non-acoustic ASW methods, although these have limitations. Magnetic anomaly detection (MAD) picks up variations in the magnetic field surrounding a submarine, but in shallow waters it is very prone to picking up false alarms. In muddy waters, forward-looking infra-red detectors (FLIR) can identify temperature differences between a submarine’s wake and the surrounding sea, but it cannot differentiate between those and irrelevant heat sources, such as industrial effluent, commercial ship wakes and river outflows. Radar is an important means of SSK detection, although developments in SSK technology have reduced its significance. Synthetic aperture radar (SAR) will pick up an SSK’s periscope and snorkel easily. But for SSKs the development of air independent propulsion (AIP) has reduced the frequency of battery recharges. Fire-control systems have removed the need for an attack periscope and modern periscopes reflect almost no signal. The blue-green laser has yet to penetrate below a depth of 50 metres so research into this technique has some way to go. There is no evidence that Soviet research into fluorimetric devices that detect a submarine by its wake passing through water, have yielded useful results. The same applies to work on bioluminescence, tracking a submarine by the disturbance it causes to micro-organisms. Finally the autolusus, or sniffer system, that uses chemical detectors to pick up combustion products emitted by diesel engines, is hampered by pollution in coastal environments. Once an SSK is detected the next task is to destroy or disable it. The time between detection and firing a weapon is seconds rather than minutes. The tactic of hunting to exhaustion, forcing an SSK to snorkel to recharge its batteries, is less likely to work in coastal waters. The weapon favoured by Swedes in shallow water conditions is anti-submarine mortar, although its range is limited. Depth charges are regarded as a viable alternative. Some argue that the objective in coastal waters is not to destroy the SSK but to deny it the use of areas of sea where interventionary forces wish to operate. In this respect, the underwater mine, such as the UK’s Sea Urchin or Stonefish, may well provide a solution. These can discriminate between targets and reject countermeasures. So submarine denial can be achieved by laying mines either side of a channel that amphibious forces plan to use. Big threat from small subs Invented 125 years ago, the torpedo is the most common anti-submarine weapon although green and brown water conditions have degraded the effectiveness of sophisticated homing torpedoes. The wire-guided version is the best choice, in spite of restricted range and the time needed to reload. The SSK poses a major problem to any naval or maritime forces engaged in interventionary operations. It can be hunted down only by large-scale forces using a range of acoustic and non-acoustic methods. ASW technology has received a low priority while the SSK has become much more stealthy and dangerous and interest is being expressed in small submarines that can take even greater advantage of conditions prevailing in coastal waters. To date the balance between submarine and anti-submarine technologies and tactics would suggest that the former has the edge. © |
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