A confidential briefing to UK defence chiefs has concluded that the proposed US ‘Golden Dome’ missile defence system, a $1.2 trillion programme championed by former President Donald Trump, would be unable to defeat a large-scale, co-ordinated attack from a near-peer adversary. The assessment, prepared by the Defence Intelligence Staff and shared with the Ministry of Defence, warns that the system’s architecture is optimised against limited or rogue-state launches rather than the saturation salvos that Russia or China could employ.

The finding has alarmed senior British officials who had been counting on the shield to protect NATO’s European flank as part of a broader deterrence posture. The Golden Dome concept, first publicly floated by Trump in 2023, envisions a layered network of space-based interceptors, ground-based radars and terminal-phase batteries across the continental United States. Proponents argued it would render obsolete the logic of mutually assured destruction by guaranteeing the destruction of any incoming warheads.

However, the British analysis, based on classified test data and modelling conducted by the US Missile Defence Agency, indicates that even optimistic scenarios envision significant leakage: under a salvo of more than 200 warheads and decoys, the system’s kill rate drops below 70 per cent. In an all-out exchange involving several thousand warheads, the fleet of interceptors would be rapidly exhausted, leaving major population centres vulnerable. The document notes that the US has not committed to sharing the technology or integrating it with European early-warning networks.

British defence chiefs are now pressing Washington for a revised architecture that emphasises resilience and allied interoperability. A Ministry of Defence spokesman declined to comment on the contents of the briefing but stressed that the UK remains committed to working with the US on missile defence. The assessment is likely to reignite debate over the wisdom of massive investment in missile defence at a time when peers are expanding their arsenals.

Critics have long argued that such systems fuel arms races; proponents retort that they are a necessary hedge against accidental or unauthorised launches. For now, the Golden Dome remains a conceptual programme without full congressional funding. But the British analysis suggests that even if built, it would not deliver the absolute protection its name implies.