Currently, Britain’s nuclear arsenal is entirely based on four Vanguard-class submarines, each armed with 16 Trident II multi-warhead nuclear missiles. At any given time, at least one Vanguard is on standby patrolling the Atlantic. What would happen to the Vanguards (and their arsenal) if the Isle of Man were suddenly and utterly destroyed and there was no one left to take orders from the Vanguard?

The UK was the third country in the world to successfully test nuclear weapons (VKHN) and is one of five countries recognized by the Nuclear Non-Proliferation Treaty (NPT) as possessing this type of weapon. Like other nuclear powers, the UK possesses nuclear weapons for deterrence purposes, because everyone understands that a nuclear attack means the total destruction of all parties and possibly the whole world.

Therefore, the UK must of course have strict control procedures to ensure that Trident missiles are not launched by “mistake” or “on a whim”.

A Royal Navy Vanguard submarine. Photo: Royalnavy.mod.uk.

As a constitutional monarchy, the British Prime Minister holds great power, including the right to order the use of nuclear weapons (although the Queen remains commander-in-chief of the armed forces). Under normal circumstances, the Prime Minister gives the order to launch by sending a code to the Royal Navy's Northwood Command. After careful verification, Northwood then relays the order to the Vanguard submarines on standby in the Atlantic. It should also be emphasized that every step in the process of initiating a nuclear attack requires two people (the two-man rule), including the Prime Minister's order.

If there is sufficient reason to believe that the Prime Minister has given an order while in a state of insanity or without a valid reason, the Chief of the General Staff can take necessary measures to nullify the order and avoid a massacre. British Prime Ministers also designate a senior Government official to act as a replacement if the Prime Minister becomes incapacitated, for example by assassination.

Under normal circumstances, yes. But what if Britain were attacked first and the entire government was wiped out? What would happen to the Vanguards still at sea and the dozens of Tridents they carried? This is where the Letters of Last Resort come in.

The Last Letters is the name given to four identical letters, placed on four Vanguard-class submarines. They contain instructions from the British Prime Minister on what to do once the British Government ceases to exist and the Prime Minister (and his designated replacement) is dead. The instructions can fall into one of four categories: respond with nuclear weapons; do not respond; the captain makes his own judgment; or hand over control of the ship to an ally (possibly the United States or Australia).

When a new British Prime Minister takes office, the first thing he or she must do is write four "Last Letters". For many new Prime Ministers, this is when they feel the full power and responsibility of the position they have just sat in. Some are even shocked when they have to make a choice that can affect millions of lives on their first day in office.

The letters were kept on the submarine in two safes. The codes to open the safes were held by two different people. Usually the captain held the outer code, and another commanding officer held the inner code. When the Vanguard was out of contact with the mainland for an extended period of time, the captain would carry out a series of checks before confirming that Britain had suffered a devastating nuclear attack (including confirming that BBC Radio 4 had been off the air for at least four hours). Only then would the “Last Letter” be opened, and this was the final order from the British government.

To date, none of the letters have been revealed, as they were all destroyed as soon as a British Prime Minister left office. The first to speak (indirectly) about their contents was the Prime Minister of the Land of Fog from 1976-1979, Lord Callaghan. He said in an interview with historian Peter Hennesy:

“Having to use nuclear weapons means that the goal of deterrence has failed. This weapon really has no other meaning than deterrence. But, if there is absolutely no other choice, I will use it! I also tell you this, assuming I somehow survive after the order is carried out, I will never forgive myself.”

According to qdnd.vn