The Queen was expected to urge Britons to pray and remain united and resolute in the event of the "madness" of nuclear war, papers from 1983 show, informs BBC.
The script for a hypothetical broadcast has the monarch describing the threat to the "brave country" as "greater" than any other in history.
It also mentions the Queen's son Prince Andrew, then in the Royal Navy.
The speech, devised by Whitehall officials at one of the most fraught Cold War periods, was never recorded.
The document, released by the government under the 30-year rule, was drawn up as part of a war-gaming exercise in the spring of 1983, which worked through potential scenarios.