On the day of Russia’s full-scale invasion of Ukraine in February 2022, Anton says the nuclear weapons base he was serving at was put on full combat alert.

“Before that, we had only exercises. But on the day the war started, the weapons were fully in place,” says the former officer in the Russian nuclear forces. “We were ready to launch the forces into the sea and air and, in theory, carry out a nuclear strike.”

I met Anton in a secret location outside Russia. For his own protection, the BBC will not reveal where. We have also changed his name and are not showing his face.

Anton was an officer at a top-secret nuclear weapons facility in Russia.

He has shown us documents confirming his unit, rank and base.

Our source for this story,the BBC is unable to independently verify all the events he described, although they do chime with Russian statements at the time.