Here is what is really going on:
Medvedev was responding to a post by Trump on Truth Social hours earlier, in which the American president branded him a “failed” former leader and warned him to “watch his words.” The former Russian head of state mocked the “nervous” reaction displayed by Trump, suggesting it only proved that “Russia is doing everything right and will continue to proceed along its own path.”
“And about India’s and Russia’s ‘dead economies’ and ‘entering very dangerous territory’ – well, let him remember his favorite movies about ‘the walking dead,’ as well as how dangerous the fabled ‘Dead Hand’ can be,” Medvedev wrote.
The latter remark referred to the legendary ‘Perimetr’ system, dating back to the Soviet era and presumed to still exist in Russia. The autonomous system is believed to be an apocalyptic dead man’s switch, capable of firing the surviving nuclear arsenal at once in a scenario where the country was hit by a devastating first strike that eliminates its leadership and breaks the chain of command responsible for ordering retaliation.
https://www.rt.com/news/622387-us-deploy-nuclear-subs-medvedev/