The Enduring Importance of Anti-Submarine Warfare

7 MINS READJul 24, 2012 | 10:36 GMT

Editor's note: Rim of the Pacific (RIMPAC), a multinational maritime exercise conducted every two years around the Hawaiian Islands, is being held June 27-Aug. 7. This year's exercises mark an important step in the projection of power and interoperability between participating nations as the United States begins its strategic shift toward the Pacific region, particularly with regard to China, the region's rising power, which was not among the 21 nations invited by Washington to participate. This series analyzes the naval capabilities displayed during the exercises and weighs them in the context of regional relationships. Click here for parts onetwo, three and four

As the United States allocates additional resources to support its new strategy in the Western Pacific, the U.S. military will need to contend with operational dynamics beyond those pertaining to counterinsurgency, which has been the focus of its efforts for the past decade. Extended sea lanes dominate the maritime geography, requiring air and naval assets to play a major role in the projection of force.

Among the most important of these assets are submarines, which are increasingly crowding the waters of the Western Pacific. Well aware of the regional proliferation of submarines, the U.S. Navy and other navies in the region are developing and focusing on anti-submarine warfare (ASW) capabilities. The United States and Japan maintain the strongest such capabilities in the Western Pacific, but the Chinese have been strengthening their own anti-submarine forces. ASW capabilities are difficult and expensive to develop, but regional navies will remain vulnerable to threats posed by submarines without such investments.

Modern Anti-Submarine Warfare

World War I marked the advent of anti-submarine warfare. Threatened by Germany's unrestricted submarine warfare campaign, the United Kingdom developed an effective means of finding and destroying the boats. Anti-submarine warfare expanded in World War II, when new tactics and equipment such as patrol aircraft, radar and sonar systems and escorted convoys enabled Allied forces to subdue the German submarine threat. Modern anti-submarine warfare is complex and difficult, involving multitudes of disparate sensors and platforms ranging from aircraft to sonobuoys (expendable sonar systems) to other submarines. 

The difficulty of modern anti-submarine warfare is apparent in the Western Pacific, which consists of a mix of shallow, littoral waters and deeper waters. Anti-submarine warfare is far more difficult to wage in the noisy and contact-dense littoral environments typical of the South China Sea and the East China Sea. In these areas, acoustic energy from passive and active sonar propagation is more likely to reflect off the seabed than in deeper waters, such as in the Philippine Sea. Thus, U.S., Japanese and Chinese submarines operating in shallow waters will be better able to operate undetected, but they will also lie within closer range of land-based ASW aircraft. Chokepoints are also a major consideration in a Western Pacific ASW campaign, with the Ryukyu Islands passageway and the Luzon Strait providing the main access points for Chinese vessels into the Philippine Sea.

The United States

The United States improved its anti-submarine capabilities during the Cold War to contend with the large Soviet submarine fleet. Washington developed versatile helicopters that could easily take off from medium and large ships, as well as long-range weapons, such as anti-submarine torpedoes. It also deployed advanced detection sensors in strategic naval chokepoints such as the Greenland-Iceland-United Kingdom gap.

Threats posed by submarines decreased markedly after the end of the Cold War, but the need for ASW capabilities re-emerged recently due to the spread of diesel-electric submarines. The emphasis on supporting land wars in Asia over the past decade has led the U.S. Navy to neglect the continuous development of its ASW skills. According to the Navy, P-3 Orion aircraft, which are well suited to anti-submarine warfare, have spent three to four times as much time conducting intelligence, surveillance and reconnaissance over land since 2001 as practicing ASW operations. Prior to 2001, the Orion fleet spent twice as much time training in anti-submarine warfare than in general intelligence, surveillance and reconnaissance operations.

However, the U.S. nuclear-powered attack submarine fleet remains particularly deadly in an ASW capacity. During the Cold War, U.S. attack submarines were charged primarily with tracking and hunting down Soviet nuclear attack and ballistic missile submarines. Thus, the U.S. navy gained a substantial amount of ASW institutional knowledge and, unlike the P-3 Orion fleet, U.S. attack submarines did not suspend their ASW training over the past decade.

The United States had hoped to deploy littoral combat ships, which are particularly adept at shallow-water operations. The diesel-electric submarines currently produced en masse by China mostly operate in littoral zones. However, there have been developmental delays in the littoral combat ships' ASW module, which is not expected to enter service until 2016.


Still, the United States is in a markedly better position to conduct anti-submarine warfare than China, which has only limited ASW capabilities, particularly against a force like the U.S. Navy. During their attempts to bolster their anti-access/area-denial capabilities, the Chinese have recognized the need for enhanced ASW operations. However, China is merely entering this stage of naval development, and it lacks the assets and institutional knowledge of the United States.

Currently, there are no major surface vessels in the Chinese navy optimized for anti-submarine warfare. China also lacks anti-submarine aviation platforms. Cognizant of these deficiencies, the Chinese have been strengthening their capabilities by intensifying ASW exercises and developing new maritime patrol/ASW aircraft based on the Y-8 platform. But these measures will take years before making a noticeable impact. In the meantime, Beijing will continue to prioritize the use of naval mines to combat submarines. While potentially effective, this approach is cumbersome and inflexible.

The Chinese have made some advances in the construction of maritime enforcement vessels, some of which could be upgraded with anti-submarine equipment. Given the large number of these vessels, such upgrades could provide Beijing with a large, if less-efficient and less-trained, anti-submarine force.

Moreover, China has developed improved sonar array technology for submarine detection. The Chinese have also expanded their investments in sea floor mapping, which will provide them with better situational awareness about the conduct of submarine and anti-submarine operations. But despite these efforts, anti-submarine warfare will continue to be the weakest aspect in China's anti-access/area-denial arsenal for the foreseeable future.


As an island nation, Japan is fully dependent on sea access for its imports and exports. Having suffered heavily from an effective U.S. anti-submarine campaign during World War II, Japan understands the gravity of a submarine threat. Indeed, Tokyo has been prioritizing development of ASW capabilities since before the Chinese and others began expanding their Western Pacific submarine fleets.

As early as 1977, Japan purchased and subsequently produced the P-3 Orion aircraft. Currently, Japan boasts the second largest fleet of maritime patrol/ASW aircraft in the world (behind only the United States), and the bulk of Japan's naval aviation is committed to ASW operations. Japan also possesses several modern ASW surface combatants, such as the Takanami class destroyers, and is developing the Kawasaki P-1 aircraft to replace the slower and older P-3 Orions.

China's advances in fielding modern submarines over the past decade has prompted Japan's Maritime Self-Defense Force to devote much of its training to anti-submarine warfare, particularly in exercises combining surface vessels, aircraft and submarines. Anti-submarine warfare remains one of the core competencies of the Japanese navy. In the future, the Japanese are set to invest even more resources and training in maintaining and enhancing this capability.

Given the large numbers of advanced submarines being developed by most Western Pacific countries, enhancing and developing ASW capabilities is critical — especially for the United States as it bolsters its presence the region. The United States and Japan are particularly concerned with China's growing undersea threat, and China increasingly is seeking to improve its ability to deter threats posed by U.S. submarine in counterintervention scenarios. All sides will ensure that their anti-submarine capabilities endure.

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