RUSI press release

“Supporting the strategic deterrents of Europe’s two nuclear powers by providing the ability to disable the Russian BMD [Ballistic Missile Defence] system represents both a comparatively modest and strategically vital function for prompt strike capabilities.” 

This is according to Conventional Prompt Strike in European Military Power, a new RUSI research report by Dr Sidharth Kaushal, which says enhancing Europe’s long-range precision strike capabilities is becoming critical to safeguarding the credibility of Britain and France’s nuclear deterrents.  

The report says that as Russian missile defence systems, such as the A-235 and S-500, around Moscow improve, the longstanding assumption that a limited number of submarine-launched ballistic missiles from Britain’s and France’s nuclear deterrent will penetrate layered defences may no longer hold.  

The paper says the European ability to defeat or suppress Russian air and missile defences around Moscow through conventional prompt strike (CPS) capabilities, using medium-range ballistic missiles (MRBMs) and hypersonic glide vehicles (HGVs), must therefore be the “irreducible minimum” mission requirement for maintaining Europe’s assured credible nuclear deterrence. 

The report says that unlike the United States, Europe’s nuclear powers lack the scale of forces required to guarantee saturation of a robust, multi-layered BMD network and notes that Israel and the United States intercepted 90% of two Iranian ballistic missile salvoes of approximately 200 missiles each in 2024. 

The research also finds that, beyond this critical function, factors which are driving down the cost of both building and enabling missiles could also allow them to be fielded at a scale which means that a much wider target set can be struck. Noting the growing importance of conventional prompt strike in recent conflicts, the study sets out a series of recommendations, which acknowledge both US concerns of overstretch and a two-peer nuclear challenge, as well as European budgetary constraints.  

Key Findings

• The credibility of European nuclear deterrence depends on defeating Moscow’s missile defences. The report states that supporting Europe nuclear deterrence by degrading Russian BMD is an “irreducible minimum” requirement of Europe’s prompt strike capabilities and “would constitute both the most achievable and the most urgent application of European prompt strike capabilities…European policymakers would thus do well to plan against the irreducible minimum immediately.” 

• Layered missile defence poses a real challenge to smaller arsenals. The report concludes that “a three-tier ballistic missile defence system can be highly effective against a small to medium-sized number of targets.” 

• Prompt strike is uniquely suited to suppress hardened, defended or dynamic targets. The report says: “The qualities of speed and manoeuvrability would serve as a means of maximising probability of effect against a small but very well-defended target set”, such as Moscow’s Ballistic Missile Defences. 

Key Recommendations

• Prioritise the suppression of Russian BMD around Moscow as Europe’s critical prompt strike mission. The report argues that “prioritising this mission to the exclusion of others would be especially reasonable if the costs of missiles and availability of ISR do not substantially change.” It says ensuring that Moscow’s Don-2N radar, A-235 interceptors and S-500 components can be neutralised is essential to sustaining credible nuclear deterrence.  

• Develop complementary capabilities to saturate and suppress layered defences. Ballistic missiles and HGVs should be combined to increase interceptor expenditure and target key elements of the BMD. The report notes: “Ballistic missiles and HGVs should be viewed as mutually reinforcing capabilities rather than alternatives.” 

• Enhance Europe’s prompt strike capabilities incrementally. The report says: “European prompt strike capabilities should be developed incrementally, beginning with the irreducible minimum mission and expanding only as costs, industrial capacity and ISR access permit.”  It warns against trying to achieve “unattainable theatre-wide strike concepts”. 

• Europe can exploit changing economics. “The commercialisation of space-based ISR [Intelligence, Surveillance and Reconnaissance], advances in AI for data processing, and changes in defence industrial practices could substantially reduce the cost of sensing and effectors over the next decade. If missile costs fall and ISR becomes more available (independent of US support), the range of viable European concepts of operations expands significantly.” 

Conclusion

Conventional Prompt Strike in European Military Power reframes the debate on hypersonic missiles and long-range strike in Europe. Rather than presenting CPS as a purely conventional deep-strike tool, it situates the capability within the logic of nuclear deterrence. 

As Russia fields increasingly capable air and missile defence systems around Moscow, the assumption of assured penetration by smaller nuclear forces becomes less certain. In this environment, the ability to degrade or suppress those defences through conventional means becomes central to preserving deterrence stability. Prompt strike thus serves not merely as an operational enabler, but as a guarantor of strategic credibility. 

The report says that without a credible pathway to defeat Moscow’s air and missile defences with prompt strike, Europe’s independent nuclear deterrents risk erosion. With carefully prioritised and incrementally developed prompt strike capabilities, however, they can remain credible even in an era of layered defences and shifting great-power dynamics.