(CNN) With his forces retreating in Ukraine, international allies expressing concern and citizens at home fleeing partial mobilization, Russian President Vladimir Putin has reached for the threat of nuclear weapons -- and revived Western fears of atomic apocalypse.
"The territorial integrity of our homeland, our independence and freedom will be ensured, I will emphasize this again, with all the means at our disposal," Putin said in a speech last week. He added that "those who try to blackmail us with nuclear weapons should know that the prevailing winds can turn in their direction."
So, how worried should we be? Here, former British army officer and former commander of the UK & NATO Chemical, Biological, Radiological and Nuclear (CBRN) Forces, Hamish de Bretton-Gordon, explains the crucial differences between "tactical" and "strategic" weapons and why all-out nuclear war probably isn't on the cards anytime soon.
The views expressed in this commentary are his own.
CNN: What's the difference between a 'strategic' and 'tactical' nuclear weapon?
De Bretton-Gordon: It is all about scale -- strategic nuclear weapons are basically Armageddon. Russia and the West (including the United States, Britain and France) both have almost 6,000 warheads each, according to the Federation of Nuclear Scientists, which is pretty much enough to change the planet as we know it. This is called Mutually Assured Destruction, with the rather ironic acronym MAD.
These warheads are fitted to Intercontinental Ballistic Missiles (ICBMs) which can travel thousands of miles and are aimed at key sites and cities in the US, UK, France and Russia.
Tactical nuclear weapons meanwhile are much smaller warheads with a yield, or explosive power, of up to 100 kilotons of dynamite -- rather than roughly 1,000 kilotons for strategic warheads.
That said, tactical nuclear weapons could still create huge amounts of damage, and if fired at a nuclear power station -- for example Zaporizhzhia in southern Ukraine -- could create a chain reaction and contamination on a scale with a nuclear strike.
CNN: What shape are Russia's nuclear weapons in?
De Bretton-Gordon: This is difficult to tell for certain, but my assumption is that Russia's strategic weapons and ICBMs are probably in good condition and always ready. It is only Russia's strategic nuclear weapons which now give it parity with the US and NATO militarily, so I expect them to be well looked after.
But this is likely not the case for the tactical weapons. The warheads and missiles are probably in reasonable condition but the vehicles they are mounted on are, I believe and have on good authority, in poor condition. Judging by the state of the rest of the Russian Army equipment on show in Ukraine, this is a fair assumption.
It is likely that these launchers would need to travel hundreds of miles to get into a position where they could attack Ukraine, as they only have a range of up to 500 kilometers (310 miles). But from a mechanical perspective it's unlikely, in my opinion, that they would get that far.
Also, it is likely these weapons rely on microprocessors and other high-tech components which are in very short supply in Russia -- given international sanctions and the heavy use of precision guide missiles by Russia, which also use these parts.
CNN: What about strikes on nuclear stations?
De Bretton-Gordon: As Putin's conventional warfare is struggling in Ukraine, I expect the Russians to increasingly turn to unconventional warfare.
At the heart of this move is attacking civilians rather than opposition forces. This manifests itself with attacks on hospitals, schools and 'hazardous' infrastructure, like chemical plants and nuclear power stations. If these are attacked, they can become improvised chemical or nuclear weapons.
The Russians hope that if the Ukrainian people give up, the military will quickly follow, which, in my opinion, is a highly flawed assumption -- both are showing a lot more mettle than the Russians.
We have seen several occasions in Ukraine where Russian forces appear to deliberately bomb chemical factories to cause toxic contamination.
Though blowing up these power stations would not create a nuclear explosion similar to a weapon detonation, it could spread radioactive debris and contaminate local water supplies.
Meteorological conditions at the moment indicate that all this contamination would also head west across Europe. This could be seen as an attack on NATO and trigger Article 5 -- where an attack on one ally is considered an attack on all allies -- which would allow NATO to strike directly back at Russia.
Hopefully, this possibility is something the Russian high command fully recognizes.
CNN: What's the likelihood of these nuclear scenarios?
De Bretton-Gordon: The use of strategic nuclear weapons is extremely unlikely in my opinion. This is a war nobody can win, and at the moment it does not seem likely that this regional conflict in Europe would lead to a global nuclear war which could destroy the planet for many generations.
I am sure the checks and balances are in place in the Kremlin, as they are at the White House and 10 Downing Street to make sure we are not plunged into global nuclear conflict on a whim.
I believe Putin's tactical nuclear weapons are unusable. Even if their vehicles do work, the minute they turn their engines on to move they will be picked up by US and NATO intelligence.
I hope the private discussions the Biden and Putin administrations have apparently been having are along the lines of, 'you move your tactical nukes and NATO will take them out with long range precision guided missiles'. It would appear this is the case from what Jake Sullivan, the US National Security Advisor to the White House, disclosed over the weekend.
The most likely nuclear scenario is, I believe, an attack by Russia on a nuclear power station in Ukraine. This could have a similar effect to a tactical nuclear explosion but would be easier to deny for the Russians, who accuse Ukraine of deliberately bombing their own power stations.
It is only Russia that has tactical nuclear weapons in this conflict, so it would be undeniable if they're used that Russia is responsible, and hence trigger NATO action. So degraded are Russian conventional forces, that they would likely be quickly overcome by NATO forces if it came to that, which even with Putin's other failings, presumably he realizes.
CNN: What can we learn from Russia's weapons playbook in Syria?
De Bretton-Gordon: I believe the Russians developed their unconventional warfare tactics in Syria. (Russian forces entered Syria's long civil war in 2015, bolstering ally President Bashar al-Assad's regime). I do not believe Assad would still be in power had he not used chemical weapons.
The massive nerve agent attack on August 21, 2013 on Ghouta stopped the rebels overrunning Damascus. The four-year conventional siege of Aleppo was ended by multiple chlorine attacks.
And it does not appear that Putin has any morals or scruples. Russia attacked hospitals and schools in Syria which it is repeating again in Ukraine. Unconventional warfare aims to break the will of civilians to resist, and Putin appears to be happy to use any means and weapons to achieve this.
CNN: How much does this come down to Putin's call?
De Bretton-Gordon: These weapons are doctrinally controlled at the highest levels and would require Putin to make the decision on a strategic strike.
However Soviet doctrine, which the Russians still seem to be following, allows local commanders to use tactical nuclear weapons to stave off defeat, or loss of Russian territory.
The attempted annexation of four districts through the current sham referendums makes the likelihood of tactical use very high, if these places are attacked. Though one still expects that local commanders would defer to Putin first before pressing their own equivalent of a red button.
Western military sources say that Putin is getting involved in the close battle and seems to be giving fairly low-level commanders their orders. This is extraordinary -- it appears that only now Putin has lost faith in his generals after Ukraine recaptured large swathes of the north-east earlier this year -- and suggests a broken command and control system, and a president who doesn't trust his generals.
(That said, while Russian military command on the ground appears to be failing, there is no suggestion Putin's control in the Kremlin is wavering).
Even in an attack on a power station one assumes Putin would be involved, as the West would likely construe it as an improvised nuclear weapon and act accordingly.
CNN: How should the West respond now -- and in the event of a nuclear strike?
De Bretton-Gordon: The West must make it absolutely clear to Putin that any use of nuclear, or chemical or biological weapons is a real redline issue. That said, I don't think all-out nuclear war is at all likely.
NATO must direct that it will take out Russia's tactical nuclear weapons if they move out of their current locations to a position where they could threaten Ukraine, and must also make clear that any deliberate attacks on nuclear power stations will exact an equal and greater response from NATO.
This is the time to call Putin's bluff. He's hanging on by his fingertips, and we must give him no chances to regain his hold. Russia's forces are now so degraded that they are no match for NATO and we should now negotiate, with this in mind, from this position of strength.