Russian President Vladimir Putin has triggered considerable concern after placing the country’s nuclear forces in a “special mode of combat duty”, suggesting they were moving up a level on the escalation ladder.
The problem is that there is little understanding about what this means in practice for Russia’s Strategic Rocket Force arsenal of 6,400 nuclear warheads.
In nuclear terminology it is a phrase not previously used by the country, which has the largest nuclear stockpile in the world.
Unlike the US, with its “defence ready condition” running from the lower level of “Defcon Five” to the highest, which suggests impending nuclear attack, of “Defcon One”, Russia does not appear to have a similar structured approach.
During peacetime — to avoid an accidental or rogue firing — the Russian launch process is similar to an electric circuit in that it is disconnected making use impossible.
But it is possible that Mr Putin’s words lead to the wires being connected, so that if he gives the order for a strike then it will be immediately carried out.
Part of the problem, defence experts say, is that, bar an incident in 1983, the world has not previously reached this serious juncture.
What it does mean is that Nato’s intelligence surveillance will intensify to examine whether there are signs of nuclear escalation.
Russia has four different methods of delivering its weapons of mass destruction. Hundreds of InterContinental ballistic missiles and are stationed in silos around the country, making any escalation there difficult to track.
Instead the West’s monitoring systems will be tracking Russia’s nuclear armed Typhoon or Borei SSBN submarines very closely to see if some are being hurried out of port to join at least one already deployed.
Following its “Scud-hunting” experience in Iraq in 1991 and 2003, and with Iran’s worrying missile developments, the US has a greater ability to track mobile rocket launchers.
A key escalation will be whether Russia has gone into a “dispersal” mode whereby its RS-24 Yars missiles carried on massive 18-wheel lorries disappear into forests or urban areas.
Russia has about 180 of the mobile launchers making tracking and targeting difficult for each missile which carries up to 10 warheads and has a range of 12,000 kilometres.
Intelligence analysts will also examine near-real time footage of Russia’s airfields to see if nuclear convoys from ammunition dumps are arriving to “bomb-up” the air force’s nuclear capable strategic bombers such as the Tu-160 Blackjack.
A sign of serious nuclear intent would be observing the painstaking task of getting nuclear bombs on board the aircraft.
“The problem is we've not really come this far in the nuclear scenario,” said Russia military expert Sam Cranny-Evans of the Rusi think tank. “We've not got to that next level of escalation before, so anything after that is enormously risky, therefore the Russians have to be very certain that this move is going to provide some sort of return.”
In 2010 Russian updated its military doctrine stating nuclear weapons would be launched “in response to the use of nuclear weapons” or WMDs.
But more pertinent to the Ukraine conflict is the suggestion that the warheads would be fired “in case of aggression against Russia with the use of conventional weapons when the very existence of the state is threatened”.
In this line of thinking by the experts Russia would initiate a limited nuclear exchange to make its foes negotiate for peace. Some fear that could be the threat Mr Putin is raising.
“This has to be taken more seriously than in the past,” said Russia expert Keir Giles at the Chatham House think tank. “Because if President Putin realised that on this occasion he's actually dealing with a potential major setback in Ukraine, given his retreat from reality that might give him more of an incentive to do something with incomprehensible deadly consequences.”
Ukraine crisis latest - in pictures
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A monitor displays a projectile striking the regional state administration building in Kharkiv, as the Russian invasion continues. Reuters -
People help a wounded woman in the aftermath of Russian shelling in Kharkiv. EPA -
Ukrainian emergency service personnel carry the body of a victim following shelling in Kharkiv. AP -
Students who fled the conflict rest in a refugee camp in Voluntari, Romania. AP -
Members of an Ukrainian civil defence unit pass new assault rifles to the opposite side of a blown-up bridge on Kiev’s northern front. AFP -
Civilians cross a river on Kiev's northern front. AFP -
A woman takes photos of a destroyed accommodation building near a checkpoint in Brovary, outside Kiev. AP -
The city hall of Kharkiv, damaged by Russian shelling. AFP -
Debris litters the square outside the damaged Kharkiv city hall. AFP -
A Ukrainian woman sleeps on the floor of the railway station in Zahonyi close to the Hungary/Ukraine border. AFP -
A medical worker attends to wounded man at a hospital in Brovary, outside Kiev. AP -
Refugees from Ukraine in a tent at the Medyka border crossing, Poland. AP -
Debris outside the regional administration building, which city officials said was hit by a missile, in Kharkiv. Reuters -
A student evacuated from Ukraine is embraced by her family after arriving at Tunis-Carthage International Airport in Tunisia. AFP -
Rescuers in a building damaged by a missile in central Kharkiv. Reuters -
An ambulance is visible through the damaged window of a vehicle hit by bullets in Kiev, Ukraine. Reuters -
Territorial defence members prepare to head out on patrol in Kiev. EPA -
UN Secretary General Antonio Guterres delivers a speech on screen during the opening of the 49th session of the UN Human Rights Council in Geneva, Switzerland. AP -
A policeman detains a young demonstrator during a protest against Russia's attack on Ukraine in St Petersburg, Russia. AP -
Local residents in Zhytomyr, Ukraine, prepare Molotov cocktails. Reuters -
Residents clean a bomb shelter under an out-of-service cinema in central Zhytomyr. Reuters -
Ukrainian volunteers tear cloth into strips to make camouflage nets in Lviv, western Ukraine. AP -
Part of the military convoy north-west of Invankiv, Ukraine. AP -
Mark Goncharuk, a young boy from Kiev, leaves his father behind as he travels with the rest of his family towards the border. Reuters -
People hold an anti-war protest outside the Russian Embassy in Mexico City, Mexico. Reuters -
A crater caused by shelling on the outskirts of Kiev. AFP -
People queue outside a grocery store in the Ukrainian capital. EPA -
Ukrainian soldiers stand at Maidan Nezalezhnosti, or Independence Square, in Kiev. EPA -
Vladimir Medinsky, the head of the Russian delegation, second left, and Davyd Arakhamia, faction leader of the Servant of the People party in the Ukrainian Parliament, third right, attend the peace talks in the Gomel region of Belarus. AP -
People who have fled the Russian invasion in Ukraine, clamour to board a bus bound for a refugee centre established in Przemysl, Poland. Reuters -
Hanna Pavlovna Lukasz, from Mirhord, Ukraine, said her sons, aged 12 and 8, and her 66-year-old mother had been waiting on the Ukrainian side of the border crossing with Medyka, Poland, for four days. AP -
A volunteer from Kiev prepares a rear post with trenches in the city. AFP -
A child being treated for cancer rests in the bomb shelter of the oncology ward at a hospital in Kiev. Getty -
Police officers check occupants of a suspicious car in Kiev, as Russia's invasion of Ukraine continues. Reuters -
A woman from Ukraine uses a phone to listen to a speech by President Volodymyr Zelenskyy at a refugee shelter in Beregsurany, Hungary. Reuters -
Shelves empty of bread after a curfew was lifted as Russia's invasion of Ukraine continues, in Kiev. Reuters -
Ukrainian Defence Minister Oleksii Reznikov, left, and President Zelenskyy. AFP -
Snow-covered shoes donated for those fleeing the Russian invasion of Ukraine at the border crossing in Medyka, Poland. Reuters -
People who have fled Ukraine wait for a bus to transport them away from the border crossing in Medyka. Reuters -
Norwegian soldiers of the Nato-enhanced forward presence battalion pose at a military plane as they arrive at an airport in Kaunas, Lithuania. AP -
A person fleeing Ukraine sits during snowfall at a temporary camp in Przemysl, Poland. Reuters -
Footage reportedly of Russian Buk missile system vehicles on a road before a drone strike near Malyn, Ukraine. Reuters -
An explosion after what are said to be Russian Buk missile system vehicles on a road are struck by a drone. Reuters -
The monument to Russian troops from the Second World War, after the figures’ hands were painted red, at the Red Army memorial in Sofia, Bulgaria. EPA -
The Peace Tower on Parliament Hill in Ottawa, Canada, is lit up with the colours of Ukraine’s national flag in a show of support. AP -
Russian President Vladimir Putin visits the construction site of the National Space Agency on the premises of the Khrunichev State Research and Production Space Centre, in Moscow. EPA -
A man looks out from a train, at the railway station in Lviv, Ukraine. The UN has estimated the conflict could produce as many as four million refugees. AP -
A Ukrainian boy waits for his mother after passing the border crossing point in Siret, northern Romania. EPA -
Russian policemen detain a demonstrator in St Petersburg, during a protest against the country's military actions in Ukraine. EPA -
Ukrainian soldiers at a check point in the city of Zhytomyr. Reuters -
Residents prepare petrol bombs to defend the city, in Uzhhorod, Ukraine. Reuters -
A pro-Russian fighter sits inside a tank in the separatist self-proclaimed Luhansk People's Republic, in the Luhansk region, Ukraine. Reuters -
Russian President Vladimir Putin, right, speaks to Defence Minister Sergei Shoigu, second left, and Head of the General Staff of the Armed Forces and First Deputy Defence Minister Valery Gerasimov, left, during their meeting in Moscow. AP -
Ukrainians and supporters gather during a demonstration in front of the Greek Parliament in Athens against the Russian military's operation in Ukraine. AFP -
Ukrainian Territorial Defence fighters test an automatic grenade launcher taken from a destroyed Russian infantry mobility vehicla after a battle in Kharkiv. AFP
