Earlier quoted context omitted.
Thankfully the answer is "If we are fighting another nuclear power such that they are trying to shootdown a Bomber that didn't invade their airspace or sink an aircraft carrier something has already gone horribly wrong." Pax Atomica is in effect and there is a very reason why all of the wars were proxy wars. Everybody knows that it can only end in everyone losing.
Let's hope it stays that way but I am not too optimistic.
I think partisans are the only ones who would dare and the only way that would be remotely deniable for intelligence agencies is if they don't have major unexplained resources - including training. Which I suppose is where cyber attacks could be useful in the sense of "remote chance of working without being utterly atomic suicidal" - if sensors go down long enough for low budget explosive attacks or their own weapons decide they must sink is their own ship. The later /really/ shouldn't happen if people are doing their jobs given the sheer number of at all given the munitions handling and design sins that would require to be possible makes juggling loaded guns look like the peak of caution.