Analysis by General Sir Richard Barrons, who led the UK's Joint Forces Command
The point about putting weapons at higher alert is probably more to do with putting more weapons at higher readiness, because there are always some weapons at high readiness all the time.
This is to ensure that neither Russia nor the west have the drop on their opponent.
On the question of whether Mr Putin would use nuclear weapons we need to distinguish between two aspects. First, in Russian military doctrine the idea of using a small tactical nuclear warhead (so perhaps from .03 of a kiloton up to perhaps 10 kiloton) is seen as an option for de-escalating the situation.
In this context they might conceive using a small nuclear weapon in Ukraine, but in the absence of NATO intervening with military force this seems wholly incredible.
NATO does not subscribe to this doctrine and sees the use of nuclear weapons as something separate and escalatory
The second aspect is whether Mr Putin thinks he would consider using nuclear weapons against countries outside Ukraine. He could only possibly imagine doing this if he was prepared to see Russian urban areas incinerated in response.
It seems to me that when Mr Putin raises the spectre of nuclear weapons it betrays his anger and disappointment at the progress on the ground so far, the realisation that the population of Ukraine is mostly set against him, and a real fear that he is about to fail in conditions in which he has turned not just most of the world (less perhaps China) against him but driven huge concerns about him into the lives of his own people.
If he is now crazy enough to think about pushing the nuclear button we’re going to rely on a very small number of hard-liners around him to not comply. Scary thought of the day.