Stupid, legacy calculus but calculus none the less. During the Cold war both sides recognized that a direct or near direct hit on a launch site could potentially negate any chance for retribution or follow up attacks in an otherwise limited/not all out scenario. So they counted the delivery mechanism they could identify, did some multiplication to account for misses and defenses and came up with a number. Then the other side noticed the build up, comes up with same general calculus and runs the same general math to decide how many they need. And this the goes back and forth for decades where each side is building up counters to their rivals counters. And the numbers we have now are actually a reduction from the peak of the Cold war build up.

It is mutually-assured destruction. The idea is that there are enough nukes to end all life on earth. Because if there are that many nukes, then nobody would ever use them.

That’s how the US and USSR came up with these figures when they were disarming at the end of the Cold War.

No, and we probably never will. The Russian government certainly doesn’t. When the invasion of Ukraine proper started, a lot of their equipment failed or was missing, and the military wasn’t aware. It had been sold off or just not maintained by the people in charge of it.

I’m certain the same thing has happened with the nuclear arsenal. The only time it will be used is if you already lost, so what’s the point in spending money on keeping it operational over just having the appearance of it being operational. Your enemy can’t know the difference (especially if you don’t) and it’d be bad to bet on it failing, so it serves exactly the same purpose regardless.

i believe (dont know) that civilans will never learn the actuals.

Bulletin of the Atomic Scientists (Nuclear Notebook series) i read/summarize these and have an unfounded belief they have as good a pulse as we’re likely to get.