Will Even the Most Advanced Subs Have Nowhere to Hide?

The modern race to build undetectable submarines dates from the 1960s. In that decade, the United States and the Soviet Union began a game of maritime hide-and-seek, deploying ever-quieter submarines as well as more advanced tracking and detection capabilities to spot their adversary's vessels.

That game continues to this day but with a wider field of players. In the coming months, the U.S. Navy plans to homeport the USS Minnesota on Guam. This Virginia-class nuclear-powered attack submarine is among the quietest subs ever made. Advanced nuclear propulsion like the Minnesota's gives the vessel a superior ability to operate covertly. More of its kind will be deployed by the United States, the United Kingdom, and Australia to compete with China for influence and military dominance, especially over the Indo-Pacific region.

This article is a collaboration between Foreign Policy, the global magazine of politics and ideas, and IEEE Spectrum, the flagship magazine of the IEEE.

As part of the landmark deal known as AUKUS (for the initials of its partner states), Australia will acquire, operate, and maintain three to five U.S. Virginia-class subs, each of which will cost about US $4.3 billion; an additional five subs will be a special AUKUS-class built in the U.K. and Australia using U.S. nuclear propulsion technology. In exchange for access to this technological edge, Australia has agreed to make substantial multibillion-dollar investments in the U.S. and U.K. naval shipbuilding industries. The deal could last until at least the 2050s and cost up to $368 billion.

These submarines are expected to assume a nuclear deterrence mission against China, whose nuclear modernization plans include the deployment of submarine-launched ballistic missiles capable of targeting the United States.

The People's Liberation Army Navy is the largest navy in the world, but it currently operates only 12 nuclear-powered submarines, a rather small number compared to the 67 attack subs and ballistic-missile subs of the U.S. Navy. And compared to U.S. submarines, Chinese boats are noisy and easily detected. But it won't stay that way for long. The U.S. Department of Defense claims China plans to modernize and expand its submarine forces significantly by 2035, including more stealthy submarines.

Once built, Australia's first few nuclear subs will operate for 33 years, until the 2060s, or even longer with lifetime extensions. To shore up its intended strategic advantages, the AUKUS deal also seeks to develop advanced antisub technology, consisting of sensor networks and analytics enabled by artificial intelligence (AI). This technology cuts both ways, though, and ocean transparency is increasing as a result. Some experts even think the game of maritime hide-and-seek could end by 2050.

Meanwhile, AUKUS faces more practical concerns, including a looming shortage of the highly enriched uranium needed to fuel the submarines, growing opposition to the deal's extravagant cost, and competing submarine designs that are much cheaper and just as capable for certain missions.

So, is now really the right time for nations to be investing hundreds of billions of dollars in submarine stealth?

What is submarine stealth?

In the quest for stealth, naval engineers first have to consider how their vessel might be spotted. Then they can design their submarines for maximum evasion.

There are two key steps to track a submarine, says Scott Minium, a former commander at Submarine Squadron 15 in Guam who has mentored the commanding officers of seven nuclear-powered subs. The first step, Minium says, is to detect the signature of a potential submarine. The second step is to classify it based on known signatures to determine if a submarine has been detected." Such signatures include the unique noise patterns generated by different submarine classes as well as other identifiers, and they're essential for detecting and tracking submarines.

The growing sophistication of stealth-busting tech casts doubt on continued investment in advanced submarines, each of which costs over $4 billion. Shown here are segments of a sub's hull. Christopher Payne/Esto

Noise is the most critical signature, and so engineers working on stealth technology focus on suppressing the sound waves that submarines give off, rendering their movements nearly silent, especially at slow speeds. The thousands of rubberized anechoic tiles that cover the hull of a Virginia-class submarine absorb or distort sound waves detectable by passive and active sonar, obscuring the sub's whereabouts. Similarly, vibration-damping materials reduce the sounds that the engines and turbines transmit to the surrounding waters.

Submarines have long been designed with certain geometric shapes that minimize their radar cross-section-that is, the areas seen by the radar that enable it to be detected. The addition of radar-absorbing materials on exposed parts of a submarine, such as the periscopes and antenna, also helps, allowing those parts to absorb rather than reflect radar waves.

In recent years, submarine designers have also worked to decrease the vessels' signatures associated with temperature, magnetic fields, and wake patterns. Heat exchangers and cooling systems, for example, reduce the heat generated by submarines, making thermal imaging and infrared detection by commercial satellites more difficult. To remove residual magnetic fields, demagnetization or degaussing" procedures involve driving the submarine between parallel piers and wrapping it with high-voltage cables. While that process sounds elaborate, it's increasingly necessary: Tracing magnetic signatures via underwater surveillance networks has emerged as a new way to detect submarines.

Additional advances in submarine stealth may be possible, but they are cost- and industrial-base prohibitive.

Finally, using pump-jet propulsors, Virginia-class submarines produce less turbulence in the water, making them less detectable by their wakes. Although conventional screw propellers are simpler and cheaper, pump-jet propulsors offer greater speed and agility, better efficiency at high speeds, and less noise.

Despite these innovations, Bryan Clark, a leading naval expert at the Hudson Institute, warns about an inflection point for achieving further reductions in sound and other signals due to the challenges of physics and mechanical systems." Additional advances may be possible, he says, but they are cost and industrial-base prohibitive."

Meanwhile, significant advances in detection technologies have reduced the effectiveness of submarine stealth. Today, increasingly sophisticated and distributed sensor networks collect information across multiple domains, much like the SOSUS hydrophone arrays that the U.S. Navy deployed in the Atlantic and Pacific during the Cold War. The rise of quantum sensors, which can detect delicate perturbations in the environment at the atomic level, promises even greater sensitivity and accuracy. And the AI-enabled systems that analyze sensor data can easily spot subtle anomalies in the ocean, such as changes caused by a passing submarine, which a human analyst would probably miss.

P.W. Singer, a senior fellow at the think tank New America and coauthor of the technothriller Ghost Fleet-in which Russia and China team up against the United States with a new capability to detect and track U.S. nuclear submarines from their radiation emissions-suggests that AI's ability to make sense of disparate wisps of data from a variety of sensors...will enable the detection of targets that could have remained stealthy in the past."

Other experts, including Roger Bradbury and Scott Bainbridge, claim this technological revolution has already produced unprecedented ocean transparency. If the most extreme predictions come true, the stealth of Australia's new fleet of nuclear submarines could be dead in the water less than a decade into their operational lifetimes.

Advanced tactics to preserve submarine stealth

Many experts say they're unconcerned about these incursions on submarine stealth. Naval operators, they claim, still have plenty of ways to protect the stealth of their submarines. These stealth-preserving techniques include 1) countering detection through noise, 2) deploying more underwater drones, and 3) using strategic moves to counter the objectives of the adversary.

The first strategy uses noise as a feature, not a bug. Instead of going quieter, Minium suggests, naval operators could try making more noise or finding innovative ways to change the acoustic signatures of submarines." For example, he says, We could make active sonar waves of submarines sound identical to whales."

This idea exploits the current limitations of AI systems and the ease with which unexpected shifts in the data can trick them. Slight tweaks in a submarine's signature might be enough to confuse an AI algorithm so that it misidentifies the vessel or misses it entirely. Minium says this approach relies on the fact that you need to know what you're looking for to leverage AI for finding submarines. If you can't classify the detected signature, the submarine is safe from detection."

Australia will base its AUKUS submarines at HMAS Stirling, a naval base near Perth. But the U.S. Navy would prefer to base the submarines in Guam, because it's closer to China's naval base on Hainan Island.

In addition to masking submarine signatures, navies could make greater use of inexpensive underwater drones, or uncrewed underwater vehicles. As Clark explains, UUVs are part of the move away from the traditional game of hide-and-seek to a competition of sensing and sense-making." This shift is aided by the sharp increase in civilian UUV traffic, for deploying fiber-optic cables and conducting scientific research. All that activity generates more underwater noise and makes it harder to detect individual signatures. Military UUVs, he says, can likewise create more noise elsewhere, allowing submarine signals to go undetected."

Speculating about the future of undersea warfare, Singer says the rise of smaller and cheaper uncrewed systems will allow these disposable sensors [to] also become killers if armed." Their disposability would enable countries to use them more aggressively, enter contested spaces, and mess with the data" collected by sensor networks. By flooding the zone with false signatures," Singer says, navies can expose the hunters who chase the false targets and possibly even waste away the adversary's expensive weapons systems."

Interestingly, the most recent Virginia-class submarines have been upgraded with the capability to deploy UUVs. According to the Congressional Research Service, this upgrade adds a substantial midsection containing four launch tubes for storing and launching additional Tomahawk missiles or other payloads." However, Clark and Hudson Institute senior fellow Timothy Walton caution against using precious payload space for UUVs. They instead recommend that the submarines carry much smaller, disposable UUVs that can be carried in external countermeasure launchers or lockers inside the submarine."

It's conceivable, too, that as the game of hide-and-seek becomes more difficult for everyone, navies may take offensive measures to protect the stealth of their submarines. This could entail less overt tactics for peacetime and more aggressive operations in a crisis. Clark gives an example: A boat could drag its anchor along the seabed to destroy transmission cables and still maintain plausible deniability" by making it look like an accident. The boat could then monitor the ships and UUVs that arrive to perform infrastructure repairs, gathering vital intelligence about the adversary."

AI's ability to make sense of disparate wisps of data from a variety of sensors...will enable the detection of targets that could have remained stealthy in the past."

A more subtle option, Singer says, exploits the fact that countries can't afford to deploy their undersea surveillance networks everywhere. Instead, they're creating windows of coverage and non-coverage"-for example, focusing on choke points in shallow waters where submarines are more easily detected. Other countries could then target [those] key nodes in the sensor network with cyberattacks, disrupting operation and allowing for covert passage."

To gain further advantage in a conflict, Singer adds, countries could assume control of a network while still making it appear fully operational and deliver false signals to the adversary." Referred to as spoofing, this tactic involves disguising a fake data source as legitimate. GPS spoofing has become a major challenge on the high seas. One high-profile incident in 2021 involved the faking of British warship positions by an unknown actor. In other situations, Singer says, an adversary might decide to simply destroy the sensors and surveillance platforms."

The AI-enabled systems for processing and analyzing massive volumes of data can also become a target. Data poisoning, for example, involves covertly contaminating the data used to train an AI algorithm, which would lead to false results. Of course, to engineer such an attack, Clark says, an adversary would probably need physical access to get around firewalled systems. Another route for data poisoning would be to use radiofrequency transmissions to attack a network and insert bad data at the source."

Opposition to the AUKUS deal

The AUKUS submarine deal represents a targeted strategy to blunt China's influence in the Indo-Pacific region and upset any plans for attacking Taiwan. Jamie Kwong, a fellow at the Carnegie Endowment for International Peace, suggests that the AUKUS subs will be able to hold China's nuclear-armed ballistic missile submarines (SSBNs) at risk."

Chinese officials, for their part, have repeatedly criticized AUKUS, warning that the security pact will increase regional tensions. China has a ways to go to catch up with the West, says Yanliang Pan, a research associate at the James Martin Center for Nonproliferation Studies, in Monterey, Calif. But it seems they're well on their way." That's unsurprising, given the long lead times for building nuclear submarines. According to publicly available reports, Pan says, China's plans include a rapid expansion in its sea-based capabilities with a nuclear-powered carrier fleet and a new prototype nuclear reactor that will be outfitted in its new [nuclear attack and ballistic-missile submarines]."

Current projections suggest China may soon overtake its adversaries in the total number of advanced submarines and come closer in terms of stealth. According to military experts, the new Chinese submarines' designs have benefited from Russian propulsion expertise, and will be much quieter, making it harder for the U.S. Navy to detect and track them.

The USS Vermont Virginia-class submarine undergoes sea trials in 2023. General Dynamics Electric Boat

Moreover, China's overall shipbuilding capabilities and pace of construction far exceed those of the United States, which currently produces an average of 1.2 nuclear-powered boats a year at the Navy's two submarine shipyards. To fulfill the terms of the AUKUS deal, the United States needs to boost the pace of production to at least two per year.

Already, U.S. capacity to implement the first pillar of AUKUS, which involves providing Australia with Virginia-class nuclear attack submarines, hangs in the balance. The U.S. Navy included the procurement of only one Virginia-class submarine in its budget request for fiscal year 2025, although the U.S. House of Representatives later advanced a defense spending bill that restored the number to two. In the immediate aftermath of the U.S. presidential election, it remains unclear how defense funding politics will play out. But it seems unlikely that AUKUS members will be able to outcompete China on nuclear-powered submarine production.

Deploying more advanced submarines won't be enough in any event. The United States, U.K., and Australia will also need to anticipate how China might disrupt their desired outcomes.

AUKUS members may decide to counter China's strategy by investing in more asymmetric means for conducting antisubmarine warfare. Presumably this is the rationale behind the second pillar of AUKUS, which explores deepening collaboration on emerging technologies such as artificial intelligence, quantum computing, cyber capabilities, and hypersonic weapons. It also takes advantage of China's delayed start in developing advanced sensing capabilities.

Using such technologies, AUKUS members could, for example, exploit weaknesses in China's shallow seas and choke points surrounding its shores. The United States and its allies could also counter Chinese submarines' ability to reach deeper waters undetected by deploying quantum-based sensors, jamming, UUV detection, and AI-enabled analytics.

If the most extreme predictions come true, the stealth of Australia's new fleet of nuclear submarines could be dead in the water less than a decade into their operational lifetimes.

However, if they're leveraging emerging technologies to detect China's submarines, will AUKUS members even need the exquisitely advanced submarines from the United States?

George M. Moore, scientist-in-residence at the James Martin Center for Nonproliferation Studies, notes that the Virginia-class submarines do not seem optimized for the shallow waters of the South China Sea. Australia might have been far better off building more conventional diesel submarines, which are quieter than nuclear-powered submarines when running on battery."

Nuclear-powered submarines can stay underwater longer than diesel subs can, so they are considered the stealthier option, as the chances of detection increase every time a submarine surfaces. But, Moore says, submarines that use a newer nonnuclear propulsion, known as air-independent propulsion (AIP), pretty much eliminate that advantage with their capability to stay submerged for up to 30 to 40 days." Unlike conventional diesel submarines, AIP subs operate on battery for long periods, do not require regular access to oxygen, and do not need to surface or use a snorkel as frequently.

Going with AIP submarines rather than Virginia-class nuclear subs would save several billion dollars per vessel. That might offer Australia a more viable alternative for covering the shorter distances in the South China and East China seas, with the other two AUKUS members tracking Chinese submarines in deeper waters.

Moore also has reservations about the nuclear deterrence mission of the AUKUS deal. To execute that mission, an AUKUS submarine would need to trail any Chinese ballistic-missile submarine coming out of port before it goes silent. But we just don't have the numbers to do this anymore," he says.

Is AUKUS a good deal?

Ultimately, the future of AUKUS may hinge on more practical matters than any perceived decline in submarine stealth. In the near term, the Australian government must refurbish its HMAS Stirling submarine base in Western Australia, to allow for the rotational deployment of five U.S. and U.K. nuclear attack submarines. That will cost about AU $8 billion. But the plan may face difficulty due to growing domestic skepticism about the deal and its enormous expense.

The plan may also face opposition within the United States. The naval base in Western Australia is further from the South China Sea than Guam is, which the United States favors for its submarine operations, Moore says. Guam is also closer to China's submarine base on Hainan Island.

Moreover, there's a declining stockpile of the highly enriched uranium (HEU) that Australia's new subs will use for fuel. For many years now, U.S. nuclear-powered submarines have run on the HEU scavenged from old nuclear weapons," Moore says. Under AUKUS, this limited fuel stock would presumably be shared by the United States, U.K., and Australia. Building a new enrichment facility, he says, could take up to 40 years.

Then there's the issue of Australia accepting HEU for its new nuclear-powered submarine fleet. Under AUKUS, Australia will become the first nonnuclear-weapon state to operate submarines with weapons-grade material. However, Kwong of the Carnegie Endowment for International Peace notes that Australia doesn't have a nuclear-energy industry, and so is unprepared for handling spent fuel." Indeed, since 1998, Australian federal legislation has banned the development of nuclear power, including a prohibition against nuclear-fuel-related facilities.

Whatever happens to AUKUS, advances in AI, drones, and sensing technologies are rapidly changing the dynamics of undersea warfare, which will force many nations to rethink their submarine strategies and investments. As the game of hide-and-seek gives way, new strategies may hinge more on asymmetric innovations than on submarine numbers and stealth-regardless of how sophisticated those submarines are.

This article is a collaboration between Foreign Policy, the global magazine of politics and ideas, and IEEE Spectrum.

A correction to this article was made on 19 December 2024 to fix an editing error. Passive sonar does not emit sound waves.

This article appears in the December 2024 print issue as No More Hide-and-Seek."