A secret military convoy was sighted travelling along the motorway near Glasgow on Friday.
The vehicles could have been carrying up to six deadly nuclear warheads.
They were believed to be headed to the Royal Naval Armaments Depot Coulport on Loch Long.
Spotted by an organisation that tracks and monitors the convoys that transport the UK's Trident nuclear warheads, NukeWatch, the convoy was around a mile from Glasgow.
A spokeswoman for the campaign group said: “'I think there were four warhead carriers I believe. Our reckoning is that each of those trucks can carry two but one of the trucks is empty as a spare in case breaks down”.
“There hasn't been one since October last year which is a bit strange. But there was a bit of a flurry in the end…There must be some reasoning in their madness but they'd never enlighten us [as to] what that is.”
Nuke Watch
It is understood the purpose of the warhead movement was likely for the purposes of refurbishment, rather than attempts to arm warheads ahead of a potential attack by Russia.
Since 1969, the UK’s nuclear deterrent has been delivered by the Royal Navy, with at least one nuclear-armed ballistic missile submarine patrolling the seas undetected at all times. Their purpose is to preserve peace, prevent coercion, and deter aggression.
HMS Vanguard collided with a French submarine in 2009, damaging both vessels, though no leaks of radioactive material were detected.
There have been seven accidents involving British nuclear weapons in total since 1966. None have yet resulted in radioactive leaks.
Prime Minister Boris Johnson, in a phone call with the Ukrainian president on Sunday afternoon, told Volodymyr Zelenskyy the UK was “committed to stepping up military, economic and diplomatic support” in a bid to bring about an end to the war.