Feature: UK considering second nuclear system to bolster European deterrence

A Vanguard-class SSBN, seen here returning to HMNB Clyde naval base in Scotland on 31 August 2024. (MoD/Crown Copyright)

The returning salience of nuclear weapons in international security has been illustrated starkly in the broad context of the Russia-Ukraine conflict, with Russia making thinly veiled remarks regarding potential nuclear use to either deter external actor involvement or help deliver battlefield victory.

For the United Kingdom – a nuclear power and NATO member – the war and wider deterioration in Euro-Atlantic security have prompted a fundamental rethink of its nuclear deterrent posture and force structure.

The UK possesses nuclear weapons to provide minimum, credible, independent deterrence and defence against the most extreme threats to the country and its interests, including deterrence reassurance for its European NATO allies. Since retiring its WE177 air-dropped freefall bomb in the late 1990s, the UK has delivered its deterrent via a single nuclear system – nuclear-armed Trident D5 submarine-launched ballistic missiles (SLBMs) carried onboard its Vanguard-class nuclear-powered ballistic missile submarines (SSBNs), with one of the four boats permanently on patrol in a continuous at-sea deterrent (CASD) posture.

The UK's nuclear deterrence logic is that a submarine-based capability – out of sight, but not out of mind – generates strategic-level deterrence through an assured second-strike capability. Yet, security shifts caused by the conflict in Ukraine prompted the UK to reassess its national and NATO deterrence commitments. This included considering returning to a nuclear ‘dyad' by adding an air-based nuclear weapons capability, to provide non-strategic deterrence lower down the nuclear use and escalation ladder to reinforce deterrence and security assurance for the UK's European NATO allies.

Some of the thinking around this reassessment was revealed in the UK's 2025 Strategic Defence Review (SDR),