Tracking the untrackable
How neutrino detectors may threaten submarines
Late last year, the United States (US) Defence Advanced Research Projects Agency (DARPA) publicised plans to improve existing neutrino detectors. The goal is to develop a design which is ‘much lighter, enabling mobility and deployment of detector arrays for distributed sensing’.
Neutrino detectors have been explored for monitoring nuclear reactors since the late 1970s, generating interest in their potential to enhance nuclear non-proliferation. DARPA’s miniaturised detector, however, could have implications for nuclear deterrence as well.
DARPA, the primary American body for military research and development, has not disclosed the exact nature of the programme. However, reducing the size of conventional detectors could enable more discreet deployment in shallow waters. This could enhance the detection of vessels utilising nuclear propulsion. In other words, neutrino detection may soon threaten both nuclear-powered attack submarines (SSNs) and ballistic missile submarines (SSBNs), extending beyond the monitoring of land-based reactors.
Neutrino detectors present an intriguing dual-use challenge. While this technology holds promise for both civilian research and non-proliferation, it may also have a granular impact on considerations of strategic stability. These discussions must be contextualised by geographic and operational constraints, as well as enduring deterrence principles, of course. Nevertheless, advancements in sensor and detection technologies like this should beget a more rigorous examination of whether a diversification of strategic assets – or even a shift towards conventional systems – warrants greater consideration.
From science to nuclear safeguards
Neutrinos are subatomic particles produced in vast numbers by nuclear reactors, yet they are notoriously difficult to detect. Their weak interactions have often required large-scale detectors of up to several kilotonnes. Their specific size depends on a number of variables, including monitoring distance, which can currently range from ten metres to over 150 kilometres. In turn, larger designs, including existing arrays in the Mediterranean or South China Sea for example, which leverage natural bodies of water, often remain stationary. Still, sea-based and even handheld mobile solutions already exist, and could be further improved according to intended use cases.
The International Atomic Energy Agency (IAEA) already lists over a hundred techniques for nuclear monitoring. However, these typically rely on physical access, since techniques such as muon detection and gamma ray detection fall short at extended ranges. Additionally, shielding and water submersion need to be considered. Neutrino detectors could theoretically offer remote, near-instantaneous measurement to overcome these constraints. For example, they could enable monitoring enriched materials aboard future Australian SSNs – acquired through the AUKUS agreement with the United Kingdom (UK) and the US – without inspectors having to board these submarines containing sensitive technology. The issue, for now, remains that long-range field deployment is still technologically premature.
The threat to nuclear submarines
Should neutrino detectors become operationally viable, they could pose a novel threat to naval vessels, especially submarines. SSNs typically offer ‘superior speed, range, stealth and endurance’. SSBNs, such as those of the Royal Navy, rely particularly on remaining undetected to serve as a survivable second-strike deterrent. Additionally, Australia, Brazil and Turkey have signalled strong interest in acquiring SSNs. If SSBNs and SSNs become easily detectable by means of an effective neutrino detection system, this could influence procurement and deployment strategies.
However, the actual threat must be placed in context. Depending on the detector’s technological maturity, geographic constraints matter. Near-future miniaturised detectors are unlikely to cover vast and deep oceans. Instead, limited-range systems will more likely monitor chokepoints, or narrow and shallow waters. For the UK, the US, France and India, this would imply delayed consequences, given their easier geographical access to deep waters. By contrast, Russia and the People’s Republic of China are more constrained by the Greenland-Iceland-UK (GIUK) gap and the First Island Chain respectively.
Even advanced neutrino detectors will not suddenly turn the oceans transparent or replace other sensors. Chokepoints can already be monitored by traditional methods, including sonar or satellite imagery analysis. Furthermore, neutrino detectors will not aid in locating conventional submarines. Ultimately, they can only augment a broader array of improving sensor technology. These in turn are likely to generate substantial data streams, requiring sophisticated sorting algorithms, a greater power supply and protection from electronic interference.
Additionally, these sophisticated detection networks must still be accompanied by adequate chase and kill capabilities. During the Cold War, for example, the Soviet Union pooled its strategic submarines in protected zones in reaction to advanced Sound Surveillance System (SOSUS) monitoring by the US. Similarly, Chinese SSBNs are escorted by attack submarines in the South China Sea today. Such operational measures could further mitigate the threat posed by neutrino detectors, depending on strike systems’ capabilities.
Implications for SSBNs and SSNs
Neutrino detection is a dual-use technology without a clear regulatory path ahead. Its potential applications in non-proliferation and science are significant, but this progress could be accompanied by strategic implications. Problematically, the effects of this technology will be experienced differently by states, and verifying the absence of detectors and lack of integration with military networks will be challenging.
Consequently, a formal regime governing neutrino detectors’ military use is unlikely. That said, behavioural norms will likely still shape military decision making. Sea-based deterrence will offer diminished value if and when SSBNs could be pinpointed in the future. However, threatening such strategic assets would still risk nuclear war. Given that the US already induced caution when Ukraine struck Russian early-warning radar systems to avoid miscalculation, similar understandings arguably apply to second-strike systems, such as strategic submarines, as well. Like land-based launch platforms, SSBNs would be left protected by the assumption of deterrence principles, rather than stealth.
For attack submarines, the debate ultimately hinges on foreseen mission requirements. SSNs can still reach higher speeds and rarely demand refuelling, even if they become detectable. Yet, this means the tradeoff – which already involves significantly higher financial costs and potential political controversy – will only get worse. Meanwhile, contemporary air-independent diesel-electric boats, such as Germany’s Type 212, are increasingly becoming better. They can stay submerged for weeks and offer reduced noise and heat signatures, due to the lack of reactor cooling systems. Indeed, conventional attack submarines have already occasionally outperformed their nuclear counterparts. If neutrino detection does indeed become operational, and spreads in the near future, this would further incentivise hedging against greater reliance on SSNs.
Jan Quosdorf is a graduate student at King’s College London and the University of Hamburg, focusing on arms control and Chinese foreign policy. He currently works for the Arms Control Negotiation Academy (ACONA) and the Helmut-Schmidt-University/University of the Bundeswehr Hamburg. He is the National Coordinator of German Student/Young Pugwash (GSYP).
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