If Kyiv has enough in its locker to strike south, Putin could be on the wrong end of a Stalingrad-style trap

‘He could use tactical nuclear weapons but that could easily end his time in power – if, indeed, the order were followed’

‘By its threat to Crimea and denying Mr Putin Odesa, Kyiv could deliver the greatest strategic shock’

UKRAINE’S lightning assault over the weekend means that for the foreseeable future the momentum in this war lies entirely with Kyiv.

Mr Putin could seek to regain the initiative, or at least stymie Ukraine’s advance, by orchestrating an accident at the Zaporizhzhia nuclear power plant; perhaps even resorting to using tactical nuclear weapons. But neither scenario is very likely and the latter could very easily end his time in power – if, indeed, the order were even followed. Either option would be incredibly reckless, though that is no guarantee Mr Putin would not turn to them. Russia’s president has form when it comes to being incredibly reckless.

In terms of battlefield movement therefore, where and when this advance halts will be decided by Volodymyr Zelensky, Ukraine’s president, on the advice of his military leadership. Their decision will largely come down to how much Kyiv has left in its locker.

Every military force should have a reserve; a grouping of uncommitted but highly trained and equipped troops, ready to address a number of tasks as emerging situations dictate.

The past week’s breakthrough, which came to the east of Kharkiv, seems to have been achieved with a force of around three brigades, about 6,000 troops. Kyiv will need at least another brigade in reserve to be able to meaningfully exploit Moscow’s sudden collapse.

Let’s assume Kyiv does have those forces, comprising of tanks, infantry, artillery, engineers, air defenders and all the other parts of the military orchestra, ready to go. How might they be employed?

Much depends on the situation on the ground as Ukrainian troops harry the retreating Russian army. Should they continue to push east into the Donbas?

Having been ignominiously ejected from the north of the country, Mr Putin declared that “liberating the Donbas” had been the main aim for his “special military operation” all along.

That was a lie, of course. Like much else he says, it was all he could grasp for in the face of Russia’s first major defeat of the war.

However, Ukraine does not, for now, have to reclaim further territory in the Donbas in order to deny Mr Putin the ability to declare the campaign a success. Attempting further advances there risks losing men and material for limited additional gain, all while exposing its logistical tail to attack from the flanks. To the south then? Crimea is arguably Russia’s centre of gravity in this war; the single location or entity that must be defended at all costs and without which the whole force crumbles.

Mr Putin has always wanted to snuff out Ukraine’s existence as an independent and economically viable state but to do this Russia has to take the whole of the south, including the port of Odesa. By its threat to Crimea and denying him Odesa, Kyiv could deliver the greatest strategic shock.

To get there a Ukrainian reserve would have to cover great distances, even if logistics support would be in friendly territory.

A Ukrainian strike south to the coast, followed by a swing to the west would deliver a hammer blow to Moscow. For Russian forces in Kherson, with Ukrainian guns in front of and behind them, it would also create a situation similar to that of the German 6th Army trapped in Stalingrad in the Second World War.

And Mr Putin knows very well how that turned out.