It is easy to forget how confidently, back in February, most observers predicted that Russia would steamroll Ukrainian forces. The country was given months, if not weeks, before surrender.

Instead, the Ukrainian army is defeating Russian troops along the entire front. Last month they wrestled more than 2,300 square miles of their country back from the invaders.¹

Russia is thought to have lost one-third of its invasion force. It is making up the numbers by rushing unwilling conscriptsSomeone who is called up to join the army without a choice., many with only a day's training, to face Ukraine's well-trained soldiers and American military technology.

If Putin loses this war, his time may be up. Russia is already creaking beneath him. Opposition is flaring up. If his country is humiliated by its neighbour, he might be toppled.

That is why some think Ukraine's success has now opened up the most dangerous phase of the war: the nuclear phase.

Alarm bells started ringing this week as footage emerged of a train of nuclear equipment moving through central Russia towards the front.

Putin is certainly not thinking of launching anything at his NatoThe North Atlantic Treaty Organisation was founded in 1949 to unite Western democracies in Europe and North America against the perceived growing threat of the USSR. It now has 31 members. enemies. If he attacks London or Washington DC, they will respond by obliteratingCompletely destroying. Russia with their own nuclear weapons. 

Ukraine, however, has no nuclear capacity of its own, so it would be unable to respond to a strike. And its Western allies would not risk an all-out nuclear war by attacking Russia on its behalf.

Russia has around 2,000 "small" nuclear weapons that it could use in Ukraine.² The name is misleading - a bomb of this size would incinerate everything within 1.6km, and scatter radioactive falloutRadioactive particles that fall to Earth after a nuclear explosion. over a much wider area.

A single blast on an important military base or city could halt the Ukrainian advance. And if Ukraine believes that Russia is prepared to obliterate it rather than lose the war, it might be persuaded to negotiate a peace deal that favours Russia.

Putin is certainly keen for the West to believe he is ready to go nuclear. In a furious speech last week, he claimed the US bombings in Japan in 1945 had set a precedent for such a move.³

However, the front is now located in regions of Ukraine that Russia claims to have annexedTake possession of an area of land without permission or by force.. It would be using nuclear weapons on what it insists is its own territory.

Moreover, prevailing windsThe most common direction the wind blows in a certain geographical area. in Europe blow from west to east: towards Russia. Nuclear fallout released in Ukraine could quickly make its way on to Russian soil.

Using a nuclear weapon would also mean crossing a line that most other countries regard as sacrosanctInviolable or beyond criticism. It derives from two Latin words, "sacro" and "sanctus", that both have religious connotations.. States that are currently friendlier towards Russia, like China and India, would likely conclude that it is an unreliable ally and sever ties. Others might be persuaded to join US sanctions against Putin.

So Putin stands to lose a great deal from actually using a nuclear weapon, but he gains from the threat of using one. It prevents the world from provoking Russia too much, and keeps the Ukrainians in a state of terror. It might be that nuclear weapons are most useful for him if he does not use them at all.

Yes: Nuclear weapons are a red line for the entire world. A tactical nuclear strike might win Russia the war but it would become a pariahAn outcast. . No other country would ever have dealings with it again.

No: The USA used nuclear weapons to win a war in 1945, and other countries simply accepted it. China and India will keep supporting Russia if it is in their interests. There is no downside for Putin.

Or... Using a nuclear weapon is too big a risk even for Putin. But the threat of using one gives him vital leverage, so he will do all he can to make others believe he might.

Conscripts - Someone who is called up to join the army without a choice.

Nato - The North Atlantic Treaty Organisation was founded in 1949 to unite Western democracies in Europe and North America against the perceived growing threat of the USSR. It now has 31 members.

Obliterating - Completely destroying.

Radioactive fallout - Radioactive particles that fall to Earth after a nuclear explosion.

Annexed - Take possession of an area of land without permission or by force.

Prevailing winds - The most common direction the wind blows in a certain geographical area.

Sacrosanct - Inviolable or beyond criticism. It derives from two Latin words, "sacro" and "sanctus", that both have religious connotations.

Pariah - An outcast.