Queen Elizabeth has a pre-written speech prepared for the outbreak of World War III.
And as tensions between the UK and Russia continue to escalate, some believe the threat of nuclear war is more real than it has been since the Cold War.
The current crisis began on March 4, when former Russian spy Sergei Skripal and his daughter Yulia were found slumped on a bench in Salisbury, England.
UK Prime Minister Theresa May said they had been poisoned by a nerve agent called Novichok, one of the world's deadliest.
While the pair remain in hospital, their prognosis is grim.
Novichok has been made in Russia for many years, and Ms May said it was "highly likely" Russia was involved in the poisoning.
She demanded that Russia explain what happened, but when the country didn't comply, she said: "There is no alternative conclusion other than that the Russian State was culpable for the attempted murder of Mr Skripal and his daughter — and for threatening the lives of other British citizens."
As a result, Britain has ordered 23 Russian diplomats to leave UK soil by next Wednesday, which is the UK's biggest removal of foreign representatives in three decades.
UK government ministers and members of the Royal Family will also not attend the World Cup in Russia in June in a further show of retaliation.
As the dispute grows, UK media have republished Queen Elizabeth's speech, which she will deliver if a nuclear war is ever declared.
The monarch's speech was initially written in 1983 during the peak of the Cold War.
It had previously been kept a strict secret under the National Archives' 30-year rule.
The sombre speech was written as if it was delivered at midday on Friday, March 4, 1983 — and while some aspects are now outdated, such as the reference to Queen Elizabeth's son Prince Andrew serving in the Royal navy, the majority remains relevant.
The speech begins by referencing Queen Elizabeth's recent Christmas message, before detailing her childhood during World War II.
It goes on to encourage British citizens to "fight off the new evil".
The speech was previously published by the BBC and has been reproduced here in full:
"When I spoke to you less than three months ago we were all enjoying the warmth and fellowship of a family Christmas. Our thoughts were concentrated on the strong links that bind each generation to the ones that came before and those that will follow. The horrors of war could not have seemed more remote as my family and I shared our Christmas joy with the growing family of the Commonwealth.
Now this madness of war is once more spreading through the world and our brave country must again prepare itself to survive against great odds.
I have never forgotten the sorrow and the pride I felt as my sister and I huddled around the nursery wireless set listening to my father's inspiring words on that fateful day in 1939. Not for a single moment did I imagine that this solemn and awful duty would one day fall to me.
We all know that the dangers facing us today are greater by far than at any time in our long history. The enemy is not the soldier with his rifle nor even the airman prowling the skies above our cities and towns but the deadly power of abused technology.
But whatever terrors lie in wait for us all, the qualities that have helped to keep our freedom intact twice already during this sad century will once more be our strength. My husband and I share with families up and down the land the fear we feel for sons and daughters, husbands and brothers who have left our side to serve their country. My beloved son Andrew is at this moment in action with his unit and we pray continually for his safety and for the safety of all servicemen and women at home and overseas.
It is this close bond of family life that must be our greatest defence against the unknown. If families remain united and resolute, giving shelter to those living alone and unprotected, our country's will to survive cannot be broken.
My message to you therefore is simple. Help those who cannot help themselves, give comfort to the lonely and the homeless and let your family become the focus of hope and life to those who need it.
As we strive together to fight off the new evil, let us pray for our country and men of goodwill wherever they may be.
God bless you all."