In the “worst-case scenario”, Russian president Vladimir Putin could deploy low yield tactical nuclear weapons if his forces failed to make a breakthrough in their invasion of Ukraine.
That’s according to Commons Defence Committee chairman Tobias Ellwood, who said Western allies needed to think now what their response would be if Putin were to use unconventional forces.
And Foreign Secretary Liz Truss has said Putin may be prepared to use “the most unsavoury means” to secure victory in Ukraine.
After the Russian leader said he was putting Moscow’s nuclear forces on a “special regime of combat duty” on Sunday (27 February) in response to “aggressive statements” from Western powers, fears of a nuclear war have been ratcheted up.
But just how likely is one?
Here is everything you need to know.
What does ‘high alert’ mean?
Putin put Russia’s strategic nuclear deterrent forces on high alert, dramatically ratcheting up the tensions in his stand-off with the West over his invasion of Ukraine.
Russian television footage showed Putin meeting with his defence minister and the chief of the general staff, and instructing them to put the nuclear deterrent on a “special regime of combat duty”.
He cited “aggressive statements” coming from Western powers and hard-hitting economic sanctions, which include the exclusion of Russian banks from the Swift global payments system, as reasons for the action.
But some experts have claimed that putting the deterrent on “high alert” is simply a formality, one that the Kremlin has chosen to make public as a way to gain a tactical advantage.
Pavel Podvig, one of the world’s leading experts on Russian nuclear forces, told The Guardian: “As I understand the way the system works, in peacetime it cannot physically transmit a launch order, as if the circuits were ‘disconnected’.
“Putin’s order could involve connecting the wires, so a launch order can go through if issued.”
In theory, the nuclear deterrents of allied countries - and even our own - could also have been placed on ‘high alert’, but since we’re not looking to threaten a perceived aggressor, it just may not have been made public.
How has the West responded?
The United States immediately denounced the latest escalation by the Russian president as “completely unacceptable”.
White House press secretary Jen Psaki accused Putin of resorting to the tactics he used running up to invasion, “which is to manufacture threats that don’t exist in order to justify further aggression”.
Boris Johnson has dismissed Putin’s announcement that he is putting Russia’s strategic nuclear deterrent on high alert as a “distraction” from the struggle his troops are facing in Ukraine.
How could ‘nukes’ be used?
Despite the alarming rhetoric, it is not believed that an all-out nuclear war is all that likely.
When Putin warned countries against involvement in Russia’s invasion for fear of consequences they have “never seen” in history, many took this to be a threat of nuclear proportions.
But in reality, that could easily apply to any number of weapons systems which haven’t been fully tested or that have never been widely used in combat.
Western officials have previously raised the prospect that the Russians could use thermobaric “vacuum bombs” which suck in oxygen to create a devastating, high temperature blast.
And even if Russia were to take the drastic steps to use nuclear weapons in combat for only the third time in human history, there are a few rungs on the ladder of severity.
If Putin did decide to use nuclear bombs, he could first detonate one over some kind of “neutral”, international area as a kind of warning shot.
Moscow-based Pavel Felgenhauer - one of the world’s leading experts on Russia’s political and military leadership - recently told the BBC that Putin finds himself in a “tight spot”.
With invasion plans seemingly not progressing as smoothly as Putin would have liked, coupled with the bite of economic sanctions, Felgenhauer said that one of Putin’s options is to “explode a nuclear weapon somewhere over the North Sea between Britain and Denmark” and “see what happens.”
Then, if fighting were to continue - and let’s be honest, there have been no signs that Nato or the West would be cowed to such aggression - the next step could be to use nuclear weapons in the theatre of war itself.
What are the effects of a nuclear bomb?
Commons Defence Committee chairman Tobias Ellwood has said that in the “worst-case scenario”, Putin could deploy low yield tactical nuclear weapons if his forces failed to make a breakthrough.
He said Russia’s attitude towards such weaponry is vastly different to that of the west, and it sees battlefield nuclear weapons as simply “a bigger bang”.
The Conservative MP told the BBC Radio 4 Today programme: “The Russian military doctrine doesn’t work in the same way as the Nato military doctrine.
“They do assume that they may use battlefield nuclear weapons and they see them as just a, if you’ll excuse the expression, a bigger bang. They don’t treat fallout in the same way we do.”
When we think of nuclear weapons, we think of city-destroying horror bombs wiping out all life for miles around. But, while those bombs do exist, nuclear weapons and devices can really be of any size.
Tactical strikes would still wipe out infrastructure and life within an uncomfortably large radius, but could be used by Russia to claim victory, yet still have a Ukraine to control when all is said and done.
For example, the smallest nuclear weapon ever developed by the US military was the W54, which could carry a yield of anywhere between 10 to 1,000 tons.
Such a weapon would produce a deadly fireball radius of around 70 metres at its lowest yield.
How likely is a nuclear war?
The most drastic level of threat would be an all-out, globe-encompassing thermo-nuclear war, an atomic battle which would render many of Earth’s ecosystems unworkable, regardless of how many lives it claimed in the immediate aftermath.
Such a scenario is unlikely, for even Putin knows that indiscriminately bombing global cities would lead to his own demise.
This “mutually assured destruction” is essentially the strongest deterrent against such a conflict, but even so, its threat is one which must be taken seriously.
In a 2018 documentary, Putin chillingly put forward the question, “Why do we need a world without Russia in it?” and some have speculated the reason for his choosing now to invade Ukraine comes off the back of a fragile mental state brought on by the isolation of the Covid-19 pandemic.
Nuclear armageddon remains unlikely - Russian has frequently threatened nuclear deployments, and experts say humanity is still further from nuclear conflict than it has been in the past - but it is still possible, and concerning.
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