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Naval warfare

Since the sea warfare is changing at a rapid pace with the introduction of best of technology into the sea borne underwater operations, most navies are finding it difficult to detect undersea activities of stealth submarines which can defy sometimes most modern technical capability of a well equipped force.

More than 35 countries are currently operating a series of modern submarines, both conventional and nuclear capable, which can operate so silently that one cannot even think about their presence in such deep waters close to coastal waters.

Submarines are equipped to defy heavy under sea current and magnetic response of seabed at times of critical moment but this appears to be a cat and mouse game where movement signature’s of a ship can be a dangerous signal for the enemy to strike.    

Since submarines are becoming easier to obtain all the time, not only by developing countries but by terrorist organizations as well, it will be hard for modern navies to battle them in deep waters where the enemy remains invisible with best of efforts. 

The worldwide submarine threat does not come only from China. The breakup of the Soviet Union helped create a surplus of submarines that became available for sale. Today Iran, North Korea, Libya, Egypt, Pakistan, Israel and Turkey are only a few of the nations that operate submarines.

Although littoral naval warfare involves a great deal of ship-to-shore communications networking, mine detection, and sea-to-shore missiles and gunfire, the coastal shallows represent some of the toughest challenges for ASW operations.

Whereas the open oceans often present a deep, vast area where picking out submarines from a comparatively quiet background is relatively straightforward, the littoral areas represent a whole different ball game.

The shallows represent a sonically diverse environment; these areas team with sea life, many commercial and military vessels operate there, sound waves bounce erratically off the bottom, and shipwrecks or rock formations can be easily mistaken for hostile submarines.

Add the tremendously quiet modern diesel-electric submarine to this mix, and antisubmarine warfare throughout the world becomes much more difficult than it has ever been before. The US which operates most number of subs is getting threatened.

The “asymmetric” nature of modern warfare makes the submarine threat even more urgent. Terrorist networks with ready access to cash are increasingly likely operators of submarines, with which they could wreak havoc on oil-tanker traffic in the Persian Gulf, or perhaps even destroy or disable an unsuspecting US capital ship such as an aircraft carrier.

The current US military emphasis on force transformation and network-centric warfare has broad potential to help improve antisubmarine warfare capabilities.

The application of networking technologies could make information on enemy submarine positions available instantly not only to military forces, but also to homeland-security forces such as the Coast Guard, and to commercial shipping companies.

Optoelectronic technologies such as fiber-optic sonar and laser radar have the potential not only to help cut through the sonic murk of coastal waters, but also to network sonar detectors in real time to yield quick information on enemy submarine speed, depth, and direction of travel.

Yet none of this will happen without a serious commitment of technological expertise, research, and money to the problem of antisubmarine warfare.

There are indications that the nation’s ASW community is waking up to the new ASW challenge. Since there is a growing rivalry between US and China in Asia Pacific region, the Chinese are slowly modernizing their naval fleets.

That has created a new round of concern. For some time, China’s military modernization has been a source of great concern for the US and its allies in the Asia-Pacific region.

American anxiety has been fueled by the double digit defense budget increas over the last decade along with the veil of mystery that covers Chinese defense spending.  

Much of these funds have been devoted to the acquisition of platforms and weapons that will allow China to implement Anti-Access/Area Denial strategies (A2/AD.) Despite the growth of Chinese economic and military power, it is in no position to challenge the United States and in particular the US Navy on equal footing.

Sea control in the face of US maritime power is still beyond the People’s Liberation Army Navy (PLAN) but sea denial is an achievable goal.

Sea denial aims not to eliminate US naval forces but drawing on the same toolkit as insurgents, aims to inflict unacceptable costs on enemy forces and erode their political will to continue fighting.

Such a strategy relies upon an asymmetric approach-confronting US surface forces with PLAN surface forces would serve to play to the strengths of the United States.

Rather, the PLAN aims to inflict unacceptable costs by focusing on the weaknesses of the United States.

Multi-layered Chinese systems, threatening US forces from the land, the surface, the air, and under the waves could threaten to deny access to key strategic areas to the United States.
Submarines, unsurprisingly, can be expected to play a significant role in Chinese asymmetric A2/AD strategies.

The inherent stealth of submarines makes anti-submarine warfare (ASW) one of the most difficult tasks facing a modern navy.

This challenge is complicated further by Chinese acquisition of new nuclear (SSNs) and advanced conventional submarines (SSKs).

When armed with advanced torpedoes, sea mines, and anti-ship missiles, even relatively unsophisticated submarines can pose a significant threat to US surface forces, including the aircraft carriers that are the heart of the US ability to project power into the Western Pacific region.

Chinese threat

China has identified a growing gap in US military capabilities since the end of the Cold War and this paper will identify some of the operational uses and missions of submarine the PLAN will likely use to exploit it.

Modernization and expansion of the submarine fleet has been a high priority for the People’s Liberation Army Navy.

Acquisitions from abroad as well as a number of indigenous development programs have added advanced conventional and nuclear submarines to China’s fleet and aircraft carrier.

In addition to bolstering the number of vessels deployed by China, the acquisition of new weapons systems have made Chinese forces a more potent threat to US and allied forces in the region.

While China has maintained a number of obsolete vessels in service, procurement in recent years has been focused on replacing outmoded vessels and increasing the size of the force.

According to the Congressional Research Service, the PLAN’s annual commissioning rate of 2.6 submarines of all types will eventually result in an undersea force of 53-79 submarines.

The final size of the submarine force will depend upon China’s choice of deploying large numbers of less costly diesel-electric submarines or acquiring a smaller force of nuclear submarines.

Beginning in the 1990s, China undertook an extensive modernization of its submarine force.  Initially, the PLAN focused on acquiring advanced submarines from abroad and purchased 12 Kilo class submarines from Russia in 2002.

In addition to foreign acquisitions, China has indigenously developed four classes of submarines including a nuclear ballistic missile submarine (Type 094/Jin-class), a nuclear attack submarine (Type 093/Shang-class) and two classes of conventional diesel electric submarines the Song and Yuan classes.

The Yuan class is believed by many analysts to be equipped with an Air Independent Propulsion (AIP) system which would significantly improve its stealth capabilities.

In addition to the new submarines that have been fielded, China is developing two additional submarine classes that represent steps towards a sophisticated submarine force.

China seems determined to develop an improved version of its indigenously produced Shang class nuclear attack submarine.

According to the US Office of Naval Intelligence report, this improved attack submarine is expected to enter service in 2015.

Advanced weapons

An improved variant of the Yuan class is also under production.  This variant is reported to be notably different from its predecessors and incorporates a number of features from the Kilo class submarines acquired from Russia.

Procurement of advanced weapons systems is key to making China’s newly acquired submarines an effective fighting force, in addition to boosting the combat capabilities of China’s current forces.

Chinese submarines are equipped with wake-homing-torpedoes which can threaten US surface forces.

Kilo-class submarines are equipped with the SS-N-27 Sizzler anti-ship missile. The Sizzler is a supersonic sea skimming missile designed to defeat the Aegis missile defense system deployed by the US Navy.

The Yuan and Song class submarines are expected to be equipped with the new CH-SS-NX-13 anti-ship missile when it completes development and testing.

As well as being able to threaten US surface vessels, Shang class submarines are capable of firing land attack cruise missiles that would allow it to threaten bases in the region and other infrastructure that support US power projection in the Western Pacific.

Chinese procurement trends suggest a preference for smaller and stealthier submarines rather than long-range endurance platforms.

While China is moving towards a blue water navy, it is capitalizing on advantages conventional submarines present to green water navies.

Conventional submarines, particularly those equipped with AIP systems, can operate with a greater degree of stealth and freedom in the waters near China than larger US nuclear submarines.

Advanced weapons systems deployed on submarines along with land based missile and air forces would serve to deny the waters near the Chinese coast to US and other combat forces.

While US submarines play an important role in ASW activities, Chinese operational planners seem to focus more on the development of anti-surface warfare (ASuW) doctrine enabled by stealthy conventional submarines.

Through the purchase and indigenous production of quiet diesel-electric boats, China intents to create a ‘ghost’ submarine force that would move silently along the Chinese coast looking for possible surface targets while avoiding encounters with the enemy’s submarine force.

The difficult underwater geography of the littoral region as well as the noise from coastal shipping, fishing, and other economic activities make it an ideal operating environment for China’s submarines.

Chinese investments in hydrographic studies enhance its knowledge of the underwater topography,
thermoclines, and other elements of the coastal area and would allow the PLAN to take full advantage of the opportunities offered by the Chinese coastal operation theater.


While Chinese operational plans and possible missions for their submarine force remains opaque to outside analysts, the limitations of their current systems suggest that submarine forces are unlikely to operate independently.

Indeed, Chinese submarine forces would work in coordination with shore based missile systems.  Given that older Chinese submarines would encounter difficulty attempting to penetrate US ASW defences to conduct anti-surface strikes under normal conditions, the PLAN would be more likely to wait until missile strikes launched from the mainland had degraded US missile defences before launching anti-ship missile and torpedo attacks.

The supersonic Sizzler ASCM fired by Kilo class submarines could threaten US surface forces if launched in sufficiently numbers, or if a Kilo managed to surprise its target.

The subsonic missiles and torpedoes carried by the rest of the Chinese submarine fleet would be easier for US forces to defeat but they could still pose a significant threat to US surface vessels after US defences were degraded by other attacks.

Older submarines including the Ming, Romeo, and Han class vessels based on obsolete Soviet designs, can also pose a threat. Such submarines could act as mine layers or as bait, bringing in US submarines and ASW forces into the range of missiles carried by more advanced Chinese submarines.

The technological developments undertaken by the Chinese submarine force have had an impact on the PLAN’s assessment of their own capabilities and roles.

The Kitty Hawk incident, in which a Chinese submarine surfaced in the midst of a US carrier battle group, suggests that Chinese submariners are confident in their ability to avoid detection by US ASW escorts.

Such incidents as well as an increasing number of submarine patrols suggest that China aims at operating its forces further afield in the region and sending the message across that China is a non- negligible maritime power in the Asia Pacific.


In 1914, despite the sinking of three British cruisers in almost the same number of minutes, naval thinking held that this new underwater threat would be short-lived, as countermeasures improved.

With the development of sonar four years later, that prophecy appeared to be coming true, leading the US Naval Institute to conclude in its Proceedings of August 1925 that the submarine would ultimately prove too vulnerable to be used in conflict.           

History, of course, tells a different story, and the cat-and-mouse game between subsea and surface combatants that began with the U-boats and continued through the Cold War era, remains to the present day.

It is an uneasy arms race which has periodically seen one or the other gain temporary advantage, but which neither side has, at least as yet, seemed able to win decisively - and the innovations in both stealth and detection technologies keep on coming.

Many of these developments have been driven by a shift in the expected battle-space. With the end of the Soviet threat, the concept of open-sea conflict between large fleets has largely faded from the West’s strategic planning, to be replaced by the expectation that future naval operations will be in littoral waters, and principally against asymmetric threats.  

This new scenario is an undeniably challenging one for anti-submarine warfare, since shallow coastal seas provide natural underwater concealment.

Moreover, as the US Naval Doctrine Command’s ‘Littoral Anti-Submarine Warfare Concept’ document explains, detection is further hampered by the global trend towards smaller, but more lethal fleets; in effect, fewer needles are scattered through a much less easily sifted haystack.

A very real need for enhanced capabilities to root modern diesel, air-independent, and nuclear submarines out of the ‘mud’ of noisy, contact-dense environments typical of the littoral, and be ready as well to detect, localise, and engage submarines in deep water and Arctic environments.

Achieving better detection principally rests on improving sonar and other sensor systems to provide greater accuracy and wider coverage areas, issues which, for example, the AN/SQR-20 multifunction towed array (MFTA) - the first new surface ship sonar array built for the US Navy in a quarter of a century - has already begun to address.  

An active and passive sonar system, it is intended for use in a variety of roles and aboard a number of different classes of vessels, specifically including those ear-marked for future littoral combat roles.

The system was also developed for use with a remote multi-mission vehicle (RMMV) snorkeling unmanned surface vehicle (USV) and although it was ultimately decided not to take this further in terms of ASW, it does give a strong hint that this may be an avenue for the future.  

Such deployment of unmanned platforms has obvious benefits in extending the mobility and range of anti-submarine detection, with multiple sets of small arrays enabling a warship to effectively control a significantly larger area, either offensively or defensively, as required.

As USV and unmanned underwater vehicle (UUV) technologies mature, adding submarine hunting to their established counter-mine role forms the logical next step in dealing with an elusive foe who currently holds the advantage.

Looking still further ahead, research at Southampton University has begun to challenge the relative security submarines currently enjoy in littoral waters, with the development of a system known as TWIPS - twin inverted pulse sonar - and based on the natural sonar of dolphins.

Scientists there have shown that a dual stream of underwater pulses can penetrate bubbles more effectively than conventional sonar and provide a significantly better detection rate-at least under laboratory conditions.

Although the work is still in its infancy, it could herald the end of easy invisibility for submarines amid turbulent coastal seas.

However, as fast as such new detection solutions are developed to give the fleeting edge to ASW, inevitably, opposing innovations evolve to help submariners elude them.

Acoustic signatures have, for instance, already been cut to unprecedented low levels with the likes of the US Virginia class attack submarines, which employ a novel propulsor design, isolated deck structures and an innovative anechoic hull coating-but even so, they can still be heard.

Future generations of submarines, are gearing up to be quieter still, particularly if the direction taken by Howaldtswerke-Deutsche Werft (part of ThyssenKrupp Marine Systems) with its revolutionary Class 212A, becomes mainstream.  

Powered by hydrogen fuel cells, these vessels offer non-nuclear, air-independent operation, are almost completely silent and radiate virtually no heat.

This, coupled with high-tech energy management, acoustically optimised equipment and non-magnetic construction, is claimed to make these submarines nearly impossible to detect.

The Holy Grail of submarine stealth, however, remains a cloaking device that would render submerged vessels invisible to sonar and, although the research is still in its early stages, it seems that nanotechnology may hold the key to turning this science-fiction staple into reality.

New technology

Naval researchers have long been interested in the ability of micro-particle nano-coatings to help minimise bio-fouling and its associated drag and turbulence, but recent work has begun to demonstrate a major potential acoustic benefit too.

The idea, in the words of Nicholas Fang, professor of mechanical science and engineering at the University of Illinois, is not about dampening noise, but to guide sound waves around structures.

If we have a coating on a submarine that bends acoustic waves before they hit the surface, guiding them around the submarine smoothly, then you won’t be able to detect a submarine using sonar.

His team has already successfully managed to demonstrate a functional acoustic cloak capable of hiding a submerged steel cylinder from a sonar sensor array in the laboratory.

While doing the same for something the size of a Seawolf nuclear submarine may still be some years off, the implications are clear - and there may be more benefits to come.

Researchers at the University of Texas are harnessing energized carbon nano-tubes to generate ultra-low frequency sound, offering the long term promise of a thin coating for subs that could provide noise-cancelling against incoming enemy pings, while additionally helping enhance the submarine’s own sonar system.

The changing nature of the game means that getting the upper hand is hard-and holding on to it, even harder.

For the moment at least, as the sinking of the ROKS Cheonan most recently demonstrated, the advantage lies underwater, but with the wake-up call sounded and the world’s navies readdressing their ASW doctrines, that may be a short-lived thing.

Developments in unmanned platforms and littoral sonar may shortly make detection easier, but all of that could, in turn, amount to nothing if acoustic cloaking becomes a viable reality - and so it goes on.

It is a ceaseless round of measure and counter-measure, but in the end, even if it is a contest that no side can conclusively win, it is one which neither can afford to lose.

While the submarine forces of the PLAN have expanded and improved their technological capabilities, the ASW capabilities of the United States have eroded.

Throughout the Cold War the United States faced a persistent threat from Soviet submarines and ASW was to be a primary mission of the US Navy during a conflict as it attempted to eliminate Soviet sea based nuclear forces and ensure that sea lanes to NATO allies in Europe remained open.

The fall of the Soviet Union eliminated the undersea peer threat to the United States and ASW has not been a major component of US naval operations in recent conflicts.   The US has retained qualitative and technical superiority in the undersea domain but ASW capabilities have suffered in recent decades.

Much of the difficulty faced by US ASW forces stems from the technical challenge posed by the stealth of advanced conventional submarines.


Conventional submarines operating on battery power have a smaller passive sonar signature than nuclear submarines which must keep their reactor machinery operating.

AIP systems serve to extend the period in which SSKs can operate quietly making them more capable and more difficult to detect.

In addition to the technical challenge posed by modern conventional submarines forces, the balance of undersea forces in the Pacific is shifting.

While the PLAN expands its submarine forces, US naval forces are drawing down. The current shipbuilding plan of the US Navy envisions a reduction in submarine forces to a fleet of only 39 nuclear attack submarines in 2030, significantly less than the 48 that the Navy projected as necessary to fulfill future missions.

While US submarines are unmatched technologically, their low numbers will be a significant shortcoming due to the heavy demands that would likely be placed on them to perform both strike and ASW missions during a potential conflict between the US and China.

Other shortfalls in US ASW capabilities can also be expected. Anti- submarine warfare is a planned mission for the Littoral Combat Ship (LCS), a program which has proven to be deeply troubled.

Currently deployed LCSs have developed significant problems with structural damage due to corrosion. The LCS also lacks organic ASW capabilities and is not equipped with the towed sonar array found on previous dedicated ASW combatants.

Rather, the LCS can be equipped with an ASW mission module when necessary that is projected to include unmanned undersea vehicles (UUVs) and unmanned aerial vehicles (UAVs) that can carry out ASW missions.

The LCS mission modules are facing a number of development hurdles and are significantly behind schedule.

US aerial ASW capabilities have similarly eroded. The US retired the S-3 Viking leaving US carriers without a fixed wing ASW capable aircraft.

While the US is replacing its P-3 Orion maritime surveillance and ASW aircraft with the advanced P-8, such aircraft must operate from land bases.

While the P-8 will likely be a highly capable ASW combatant, the bases it operates from would be highly vulnerable to the types of missile and air attacks that would be integral to a Chinese A2/AD strategy.

While the US Navy faces significant challenges in the ASW arena, it has taken a number of steps to cope with the increased threat posed by Chinese and other submarines.

US naval forces in the Pacific have placed a renewed emphasis on ASW training.  As part of an effort to build greater familiarity with conventional submarines equipped with AIP systems the US conducted two years of training with the Gotland, an advanced Swedish diesel submarine.

Such training continues as part of the Diesel Electric Submarine Initiative which involves regular training exercises involving US ASW forces and the conventional submarines of allies.

While this training is a step in the right direction, exercises have demonstrated that advanced diesel submarines are highly capable threats that can threaten major US surface combatants.

PLAN submarines play an important role in Chinese A2/AD strategies. While they are not as novel of a threat as anti-ship ballistic missiles, their numbers and increasing sophistication pose a severe threat to shrinking US submarine and surface forces.

China’s submarine force is likely to expand in the future and develop increasing long-range and blue ocean capabilities that can attempt to push US forces further from Chinese home waters.