Thread by @pinstripedline

In 1992 the British Government was concerned that the US Administrations move to build links with Russia threatened the credibility of the Trident nuclear deterrent, and the 'Moscow Criterion'.

Thread on espionage, nuclear warheads and UK Trident effectiveness follows!

British nuclear deterrence is built around core idea that the UK can inflict unacceptable harm to Russian regimes core interests (e.g. Moscow). If this can be achieved, then it follows other areas can also be destroyed - 'the bomb must always get through'.

Moscow has for decades been defended by an ABM network of nuclear tipped interceptor missiles that would be fired to wipe out incoming Rentry Vehicles (RV) and keep Moscow safe. The US was relaxed about this as it could fire more warheads than there were interceptors.

For the UK, with only a maximum of 96 warheads available (2 x SSBN each with 16 missiles and 3 warheads), the ABM defences are a real challenge. By 1970s it was clear the UK deterrent wouldn't be effective. This led to the Chevaline project to ensure warheads would still make it.

This project was aided by a Soviet defector (Fedoseyev) who was an expert in the Moscow ABM radar network. After defecting to UK in 1971, he provided valuable intelligence that helped the UK work out how to penetrate Soviet defences during a nuclear attack.

By 1990s the world changed. The Bush Administration wanted to work with Yeltsin to cooperate and build trust. One option was to work on missile defence, sharing early warning data and technology to guard against wider proliferation concerns and review the ABM treaty.

In a meeting, in March 1992 Sir Richard Mottram set out the UK concerns to Richard Hadley from the US about their approach, but warned in a memo to Ministers that things looked far from reassuring. There were real concerns about the US approach here that put UK Trident at risk.

The UK set out to the USA analysis of Trident effectiveness on the UK scenario of 'going it alone'. They highlighted that UK assumptions were that of the 384 RV's that the UK would fire at Moscow, about 40-45 would make it through the defences, including some 'live warheads'.

The UK concern was that the US was too optimistic, assessing the Soviet equipment wouldn't work as well as the UK felt - allowing roughly double the number of warheads to make it through the net. Even an upwards revision as part of the ABM treaty would not be an issue.

The US push was for revision to the ABM treaty, allowing more interceptors in place to provide GPALS cover, as the successor to the SDI programme, to keep the continental US safe from an attack of up to 200 RV's at 95% certainty of interception. This meant changes to ABM treaty.

The UK concern was that if the Treaty was revised, the Russians would be able to focus their limitations on protecting Moscow, not the whole nation. This would potentially remove the ability of the UK to destroy Moscow, without significant Treaty safeguards in place.

The UK was also concerned at the US approach to offer technology transfer to Russia, which could potentially improve their ABM defences, and in turn make it harder to destroy Moscow. This was not seen as a friendly act.

More widely the UK was concerned that US proposals for missile warning data sharing could undermine NATO, calling into question the alliance, and the long term credibility of deterrence. It felt that the US was more interested in an alliance with Russia than NATO.

The UK left the US in no doubt as to its concerns, but in early 1992 there were real fears that the Pentagon would prioritise missile defence over NATO nuclear deterrence credibility. The US was told of the extent of the UK's concerns "at the highest levels in the UK Government"

In mid 1992 the Prime Minister was advised in a SECRET briefing that GPALS posed a risk to UK interests, disrupting NATO, putting the Moscow Criterion at risk, and potentially forcing unwanted commitment to GPALS at cost to UK Taxpayers.

The upshot was that if GPALS proceeded as planned, the PM was advised the UK nuclear forces would need to be expanded to still meet deterrent criteria and a 'Chevaline' type programme needed. In a post Cold War world, this would be a hard sell as defence spending was cut.

Thankfully GPALs was cancelled in early 1993, much to the relief of the British Government. It highlights that for smaller nuclear powers, arms control treaties are critical to ensuring the credibility of deterrence, and that tech transfer can be very dangerous.

The full story of how the USA nearly caused the UK nuclear deterrent to be put at risk can be found at the Pinstripedline blog "The bomber will not always get through'.

thinpinstripedline.blogspot.com/2025/02/the-bo…

Thread on UK nuclear deterrent matters may be of interest to @ColdWarPod @nukestrat @NavyLookout @fightingsailor @shashj @CorbettAndy @ajcboyd @war_student @warmatters @MTSavill @aaronbateman22 @c21st_sailor @CovertShores @cdrsalamander @Aviation_Intel @IBallantyn @MarkUrban01