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The idea of LLM Wiki applied to a year of the Economist. Have an LLM keep a wiki up-to-date about companies, people & countries while reading through all articles of the economist from Q2 2025 until Q2 2026.

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British nuclear deterrent

Britain's nuclear deterrent comprises Trident D5 missiles carried on four Vanguard-class (and soon Dreadnought-class) submarines. It can be fired "completely independently" of America, with no reliance on GPS for navigation. But for everything up to the point of firing, Britain is dependent on America.

Anglo-American nuclear co-operation

The bedrock of the relationship is the Mutual Defence Agreement (MDA) of 1958 and the Polaris Sales Agreement of 1963, which get around America's draconian laws on sharing nuclear technology. No other country enjoys remotely similar arrangements. The MDA was signed only after the Russian Sputnik shock and when Britain had demonstrated its ability to build an H-bomb.

Warheads

In theory Britain designs its own warheads at the Atomic Weapons Establishment (AWE) in Aldermaston. In practice, American and British warheads both have to fit into the same aeroshell that shields them during re-entry. Britain's Holbrook warhead is derived from America's W76; its next-generation Astraea A21 is closely linked to America's new W93. "To my best understanding the UK has never designed a modern thermonuclear weapon on its own," says Jeffrey Lewis of the Centre for Nonproliferation Studies at the Middlebury Institute in Monterey. Under the MDA, 955 non-nuclear parts of nuclear weapons were sent from America to Britain in 2020-23 alone. Britain also relies on America for tritium and for so-called interstage materials—ultralight gels that transport radiation from the fission to the fusion part of the bomb.

Missiles

Trident D5 missiles are stored and refurbished at Kings Bay in the American state of Georgia; Britain leases and picks up its missiles from that common pool. Missile testing is a joint endeavour; when a British test failed spectacularly in 2024, it was because of a problem with the American test kit.

Going it alone

If America were to sever all co-operation, Britain could hang on to one boatload of missiles at sea and another waiting to relieve it, buying a few years. Options for an independent deterrent include:

  • Building new ballistic missiles plus production facilities, which Dominic Cummings, a former adviser in Number 10, claims would cost more than £100bn.
  • Developing an air-launched nuclear-tipped cruise missile, a capability Britain gave up in the 1990s when it retired the WE 177 gravity bomb. A new warhead would need to be designed and validated without explosive testing.
  • Asking France for help. In 1990 France offered to share the design of a nuclear warhead that would fit a French air-launched missile. Britain demurred but contemplated it as "one we might revert to later".

A 2013 government review found it would take 17 years to field a new Trident warhead and 24 years for a cruise-missile warhead.

When you can flatten entire cities at a whim, a tendency towards quiet reflection and seeing-things-from-the-other-fellow's-point- of-view is seldom necessary. -- (Terry Pratchett, Small Gods)