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 surrenderTo give up or stop resisting. .

Instead, the Ukrainian army is winning battles with Russian troops along the entire front. Last month they gained 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.

Russia is already creaking beneath Putin. Many Russians are furious. If he loses the war, he might be toppled. He needs something that will let him win the war quickly and save his skin.

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 destroying Russia with their own nuclear weapons. 

But Ukraine would be an easier target. It does not have nuclear bombs of its own, and the West will not use their bombs to defend it.

Russia has around 2,000 "small" nuclear weapons that it could use in Ukraine. The name is misleading - a bomb of this size would burn 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 stop the Ukrainian advance.

However, the front is now located in regions of Ukraine that Russia claims for itself. It would be using nuclear weapons on what it insists is its own land.

Using a nuclear weapon would also horrify other countries. Some might be persuaded to join US sanctionsEconomic measures designed to punish a country, for instance by excluding it from trade. against Putin.

Yes: Nuclear weapons are a red line for the entire world. A tactical nuclear strike might win Russia the war but it would become an 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.

Surrender - To give up or stop resisting.

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.

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

Sanctions - Economic measures designed to punish a country, for instance by excluding it from trade.