Chinese sailors salute on top of a submarine. Photo: Reuters, China Daily
Chinese sailors salute on top of a submarine. Photo: Reuters / China Daily

In their quest for dominance in the South China Sea, displays of power by the US and China capture headlines. But this muscle-flexing is only the more visible part of their sparring. Much takes place out of sight, beneath the waves.

Indeed, submarines and efforts to neutralize them are a common competitive thread in these protagonists’ strategy. The role of submarines should be better understood – and the context better appreciated.

Submarines serve a critical role in battlefield information superiority. They also project power and are a deterrent to conflict. But their operations are not on the front pages unless something unusual happens, like the October 2021 grounding of the US nuclear-powered and nuclear-weapons-capable Connecticut.  

The US currently enjoys superiority in submarine technology. But the South China Sea is a confined and difficult operating environment in China’s near waters, and China’s anti-submarine capabilities are rapidly approaching those of the US there, if only from the quality of quantity. 

Indeed, submarines, both manned and unmanned, are at the frontier of the US-China contest for the South China Sea.

For China, the South China Sea is a historically vulnerable underbelly that must be turned into a “natural shield for its national security.” It hosts its vital sea lanes of communication that it believes the US could and would disrupt in a conflict. It is the focus of its anti-access/area-denial strategy, in which submarines play a prominent role.

But even more important, it provides relative “sanctuary” for its second-strike nuclear submarines that are its insurance against a first strike against it – something the US, unlike China, has not disavowed. 

China’s nuclear-weapons-capable submarines constitute its capability of a second or retaliatory nuclear strike, and any threat to them would be a red line. 

Many of the hundreds of intelligence, surveillance and reconnaissance (ISR) probes the US deploys in the South China Sea each year focus on detecting, tracking and if necessary targeting China’s nuclear submarines. China’s response has been to build up capabilities on some of the features it occupies to detect submarines as well as neutralize US ISR and thus enhance the survivability of its nuclear subs in the early stages of a conflict. 

For China, these installations are critical to its defense. Indeed, the main purpose of China’s military outposts in the South China Sea is to facilitate sustainable, redundant information superiority over the US in a conflict, particularly its submarines. The outposts comprise “an integrated South China Sea system of systems.” 

Submarine proliferation

There are already quite a few submarines already operating in the South China Sea, and their number is growing rapidly.

In 2020, the US military estimated that China had 50 diesel-powered attack submarines, six nuclear-powered attack submarines and four nuclear-powered ballistic-missile submarines. Of course they do not all operate in the South China Sea or at the same time. But in a crisis many might do so.

Of the other claimants to territory in the South China Sea, all but Brunei and the Philippines have submarines, and the latter is contemplating buying some. Russia has supplied eight Kilo-class diesel-electric submarines to China and six to Vietnam. In addition to those of the littoral countries, the US, the UK and France have deployed submarines there. 

Adding to the underwater congestion, both China and the US are increasingly using submarine drones (unmanned underwater vehicles, or UUVs) for intelligence, surveillance and reconnaissance there.  

In 2015, then-US secretary of defense Ashton Carter stated that the US was deploying “new undersea drones in multiple sizes and diverse payloads that can, importantly, operate in shallow water where manned submersibles cannot.” 

UUVs can be used to track “enemy” submarines. Indeed, China thinks the US wants to use them as a mobile “picket line” to detect and track China’s nuclear-powered and -armed submarines coming in and out of their base at Yulin on Hainan. 

Many of the US UUVs seem designed and destined to operate in, over and under foreign exclusive economic zones (EEZs), archipelagic waters and even territorial seas without permission.

Cat-and-mouse game

China is trying to catch up and has made dramatic progress in recent years. This effort is partially attributable to their utility in its “near seas” that it considers critical to its defense and security. It also may be laying an electronic underwater tripwire that can detect US submarines.

There are a least two chokepoints along routes commonly used by submarines to enter the South China Sea from the western Pacific Ocean: the Bashi Channel and the Taiwan Strait.  There they can be detected, tracked and, if necessary, targeted. 

US aircraft-carrier strike groups are often accompanied by submarines that provide advance surveillance along the routes the strike group will take. Apparently this is not always effective. On October 26, a Chinese Song-class submarine surfaced in the middle of the USS Kitty Hawk carrier strike group operating off Okinawa. The Chinese submarine had managed to evade detection by a US submarine and anti-submarine helicopters.

US carrier strike groups entered the South China Sea 10 times in 2021. Two – the Carl Vinson and the Abraham Lincoln – are operating there and practicing anti-submarine warfare right now. 

The Vinson and Lincoln strike groups passed through the Bashi Channel between the Philippines and Taiwan. China’s “massive” incursions of aircraft into the extreme southwest of Taiwan’s air defense identification zone included several varieties of submarine hunters  that monitored the Bashi Channel, likely looking for US submarines accompanying the carrier strike groups. 

In this recent cat-and-mouse game, a Chinese submarine was thought to have been in the area of one carrier strike group “to test US anti-submarine warfare capabilities.” That is why the US “sent a flurry of military planes and vessels to hunt for the submarine.” Indeed, both Chinese and US anti-submarine aircraft were observed simultaneously circling the same area looking for each other’s submarines.

The US even occasionally its uses its nuclear-powered and nuclear-weapons-capable submarines to send strategic signals to China. On January 15, the US Navy published pictures of the nuclear-arms-capable USS Nevada making a port visit to Guam. Since it is rare to publicize the location of such a critical weapon, this publicity may have been a notice to China of its second-strike deterrent operating in the region. 

Recent US strategic military moves in the region are all about improving the US edge in submarine “defense” and detection. 

AUKUS is an agreement for the US and the UK to supply nuclear submarine propulsion and underwater drone technology to Australia. A likely major use of these submarines will be to assist the US in neutralizing China’s nuclear submarines in the South China Sea. 

The agreement also calls for “rotations of US jet fighters and bombers to northern Australia” and for the potential acquisition of “more rotational basing for its submarines in Perth, Western Australia.” So the US will also be increasing its use of Australia as a base for its detection, surveillance and deterrence of China’s submarines in the South China Sea. 

China and the US are parties to the Code for Unplanned Encounters at Sea (CUES). It is a non-binding agreement reached at the 2014 Western Pacific Naval Symposium to reduce the chance of an incident at sea between the countries in the agreement, and, in the event that one occurs, to prevent it from escalating.

Given the proliferation of submarines in the South China Sea and their operations in increasingly close proximity, it is high time for a similar US-China agreement on a code for encounters between subs in that body of water.

Mark Valencia

Mark J Valencia is an internationally recognized maritime policy analyst, political commentator and consultant focused on Asia. Most recently he was a visiting senior scholar at China’s National Institute for South China Sea Studies and continues to be an adjunct senior scholar with the Institute. Valencia has published some 15 books and more than 100 peer-reviewed journal articles.