Queen Elizabeth II was prepared with a public broadcast in the eventuality of a nuclear exchange as part of an imaginary war game exercise that envisioned the Soviet Union launching a chemical attack on the UK, at the height of the Cold War back in 1983.
The speech, devised by senior Whitehall officials to announce Britain's involvement in what was feared as the Third World War, was never recorded.
"Not for a single moment did I imagine that this solemn and awful duty would one day fall to me," reads the imaginary broadcast, released here today as part of Britain's 30-year de-classification rule for classified documents.
The speech was written for broadcast at midday on March 4, 1983 and adds: "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 [King George VI] inspiring words on that fateful day in 1939 [at the start of Second World War]."
"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," the speech said.
It was part of an imaginary war game exercise, Wintex-Cimex 83, designed to seem as realistic as possible during which Orange bloc forces - representing the Soviet Union and its Warsaw Pact allies - launch a chemical weapon attack on the UK.
Blue forces - representing NATO - retaliate with a "limited-yield" nuclear strike, forcing Orange to initiate a peace process.
The exercise came in the year that US President Ronald Reagan denounced the Soviet Union as the "evil empire" and deployed US nuclear cruise missiles to Europe.
Striking a personal note, the Queen's imaginary speech went on: "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," it says.
The Soviet Union and the US later negotiated a reduction in the number of nuclear weapons, as the Cold War came to an end and averted the risk of another, potentially apocalyptic World War.