physics

Letters of last resort

Letters of last resort is a physics topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Letters of last resort rather than just read about it. In short: The letters of last resort are four identically worded handwritten letters from the prime minister of the United Kingdom to the commanding officers of the four British nuclear-powered ballistic missile submarines. The letters are stored sealed and unread on board each submarine.

Key takeaways

Letters of last resort belongs to physics; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Letters of last resort to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Letters of last resort from memory before moving on to harder problems.

Reference excerpt

The letters of last resort are four identically worded handwritten letters from the prime minister of the United Kingdom to the commanding officers of the four British nuclear-powered ballistic missile submarines. The letters are stored sealed and unread on board each submarine. They contain orders on what action to take if an enemy nuclear strike has destroyed the British government. The letters exist because the UK is the only nuclear power with comparatively little territory and a concentrated population, which make it especially vulnerable to a nuclear attack. The letters are destroyed unopened and replaced upon every change in the office of prime minister, so that their contents remain known only to the issuer.

Process A new prime minister writes a set of letters after taking office and being told by the Chief of the Defence Staff "precisely what damage a Trident missile could cause". The documents are then delivered to the submarines in sealed envelopes, and the previous prime minister's letters are destroyed without being opened. The letters do not have to be written immediately after the briefing on Trident's capabilities, and in any case the previous prime minister's set of letters remains in effect until the new letters have been delivered to each submarine. Letters aboard Polaris submarines were accompanied by a separate letter from the Commander-in-Chief Fleet which was to be opened first as it contained the conditions for opening the prime minister's letter; no such letter from the Commander-in-Chief Fleet (later Fleet Commander) has been referred to in accounts of the last resort procedure for Vanguard-class submarines. In the event of the deaths of both the prime minister and their designated "second person" of responsibility, typically a high-ranking member of the Cabinet such as the deputy prime minister or the first secretary of state, the commanders of the nuclear submarines on patrol at the time would use a series of checks to ascertain whether the letters of last resort must be opened. In 1983, the procedure for Polaris submarine commanders was to first open the Commander-in-Chief Fleet's letter if there had been an evident nuclear attack on the United Kingdom or if all British naval communications transmitted from the UK had ceased for four hours, which would then contain instructions on when to open the prime minister's sealed letter. It has been reported that the process by which a Vanguard submarine commander would determine the continued existence of the British government involves the monitoring of a variety of communication signals, with the ability or inability to receive a BBC Radio 4 broadcast having particular significance.

Options While the contents of the letters are secret, there are four "basic" options given to the prime minister for inclusion. The prime minister might instruct the submarine commander to:

Retaliate; Not retaliate; Place the ship under the command of a surviving allied country such as Australia or the United States; Use their own judgement. The Guardian reported in 2016 that the options are said to include: "Put yourself under the command of the United States, if it is still there", "Go to Australia", "Retaliate", or "Use your own judgement". The actual option chosen remains known only to the writer of the letter, the Prime Minister.

Fiction David Greig's 2012 play The Letter of Last Resort deals with the consequences and paradoxes of the letters. The play was first staged in February 2012 as a part of a cycle of plays on "The Bomb" at the Tricycle Theatre in London, directed by Nicolas Kent, with Belinda Lang playing the role of the incoming prime minister and Simon Chandler, her advisor. The production was also seen at the Traverse Theatre in Edinburgh, for the Edinburgh Fringe later the same year. The following year it was broadcast on BBC Radio 4, with the same cast, first transmitted on 1 June 2013. The KGB's attempts to obtain the contents of the letters of last resort are part of the plot of the BBC Cold War spy drama The Game (2014).

See also Cheget Dead Hand Dead man's switch Fail-deadly Mutual assured destruction Nuclear football Nuclear weapons and the United Kingdom § Nuclear weapons control Operation Looking Glass Samson Option Trident nuclear programme

Footnotes

References

External links "The Human Button". BBC Radio 4. 2 December 2008. Retrieved 10 February 2015. Rosenbaum, Ron (9 January 2009). "The Letter of Last Resort". Slate. Retrieved 10 February 2015. Radio archive: Glass, Ira (22 January 2010). "399: Contents Unknown (Prologue)". This American Life. Retrieved 10 February 2015.

Illustrations

Worked examples

Example 1 — a first encounter with Letters of last resort

Start with the simplest possible case. Write down what Letters of last resort claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In physics, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Letters of last resort before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Letters of last resort ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Letters of last resort

In research: Letters of last resort appears in physics research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Letters of last resort in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Letters of last resort is common in secondary-school and first-year university syllabi. It links to neighbouring topics Cabinet Office (United Kingdom), Emergency management in the United Kingdom, Letters written in English, so understanding it makes those chapters shorter.
In everyday life: Look for Letters of last resort outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Letters of last resort in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Letters of last resort means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Letters of last resort out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Letters of last resort in simple terms?

Why does Letters of last resort matter?

Because it connects several physics ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Letters of last resort?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Letters of last resort.