This article is a collaboration between IEEE Spectrum, the flagship magazine of the Institute of Electrical and Electronics Engineers, and Foreign Policy.
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.
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 U.S. $4.3 billion; an additional five subs will be a special AUKUS-class built in the United Kingdom 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 deterrence mission against China and its nuclear modernization plans, which 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 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, their Chinese counterparts are noisy and easily detected.
But it won’t stay that way for long. The U.S. Department of Defense claims that China plans to modernize and expand its submarine forces significantly by 2035, including by producing more stealthy submarines.
Once built, Australia’s first few nuclear subs will be designed to 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 anti-sub 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?
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, said Scott Minium, a former commander at the U.S. Navy’s Submarine Squadron 15 in Guam who has mentored the commanding officers of seven nuclear-powered subs. The first step, Minium said, 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.
Noise is the most critical signature, 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 coming from 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 a vessel 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 has emerged as a new way to detect submarines via underwater surveillance networks.
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, warned 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 said, 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 (sound surveillance system) 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 co-author 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—said that “the ability to make sense of disparate wisps of data from a variety of sensors with AI systems will enable the detection of targets that could have remained stealthy in the past.”
A report produced by other experts, including Australian National University professor Roger Bradbury and Scott Bainbridge of the Australian Institute of Marine
Science, claim that 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.
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 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 suggested, naval operators could try “making more noise or finding innovative ways to change the acoustic signatures of submarines.” For example, he said, “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 algorithm so that it misidentifies the vessel or misses it entirely. Minium said 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.”
In addition to masking submarine signatures, navies could make greater use of inexpensive underwater drones or uncrewed underwater vehicles (UUVs).
As Clark explained, 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, used both 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 said, can likewise create “more noise elsewhere, allowing submarine signals to go undetected.”
Speculating about the future of undersea warfare, Singer said that 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 said, “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 a report published in August by 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 gave 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.”
A more subtle option, Singer said, exploits the fact that countries can’t afford to deploy their undersea surveillance networks everywhere. Instead, they’re creating “windows of coverage and noncoverage”—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 added, 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 said, 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 said, 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.”
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, suggested that the AUKUS subs will be able to “hold China’s nuclear-armed ballistic missile submarines 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, said Yanliang Pan, a research associate at the California-based James Martin Center for Nonproliferation Studies. “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 said, 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 that 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.
Moreover, China’s overall shipbuilding capabilities and pace of construction far exceed those of the United States, which 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 for fiscal 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, United Kingdom, 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 anti-submarine 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.
However, if they’re leveraging emerging technologies to detect China’s submarines, will AUKUS members even need the exquisite advanced submarines from the United States?
George M. Moore, a scientist-in-residence at the James Martin Center for Nonproliferation Studies, noted that “the Virginia-class SSNs [nuclear-powered general-purpose attack 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 said, 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 expressed 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 said.
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 in order to allow for the rotational deployment of five U.S. and U.K. nuclear attack submarines. That will cost about $5.2 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 farther from the South China Sea than Guam, which the United States favors for its submarine operations, Moore said. Guam is also closer to East Yulin Naval Base, China’s only ballistic-missile submarine base, which is located 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 said. Under AUKUS, this limited fuel stock would presumably be shared by the United States, United Kingdom, and Australia. Building a new enrichment facility, he said, 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 noted that Australia doesn’t have a nuclear energy industry, and thus “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.
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