I get that it's better than just sitting there getting vaporized, and could protect from some shrapnel, debris if you're far enough away from the blast.
I also think it had as much to do with keeping the populace calmed down, having them think they could do something to effect their survival, or at least give them something to believe in to prevent mass pandemonium, as it did actually surviving some nuclear blast. All cities of appreciable size were targets, and no school desk was going to keep the people in them from getting vaporized.
Once again, no one is getting "vaporized". People need to stop perpetuating that myth. If you're at ground zero you may get severe burns, your lungs burst, or a building dropped on top of you, but you're not getting vaporized. That is, and always has been, Hollywood nonsense.
And yes, I'm sure panic reduction/avoidance was a component, but it's not just make people "think" they can do something to prevent/reduce injuries, taking those actions do prevent/reduce injuries.
If I had a dollar for everytime someone on this posted about how they live next to a primary, top-10, or first-strike target... well, I'm not saying I'd be rich, but I'd have a damn good time at a strip joint. In reality you may think you know where those nukes are going to land... but you don't. Just like no one knows what tonight's lotto numbers are going to be. Even if you know every number that is available, you don't know which ones will be picked, and in what order. Even the Russian and Chinese targeting geeks don't know. They may know what's in the database, but they certainly have more than one warplan so even they won't know which plan or targets will be selected.
Nothing like wondering if each day is going to be some apocalyptic end of the world where our friends in the cities get instantly erased while we live to die some slow painful radiation poisoning death. Or maybe we make it and just start growing a third arm out the side of our neck and have babies born inside out.
Was a strange time.
Yep, and then all of the sudden, it ended... for a little over a decade. Look man, I get it. I grew up during the tail end of the Cold War, not being able to sleep some nights as a kid because I was worried about nuclear war. But you know what? I eventually grew out of it and came to see that defeatist and fatalistic attitude for what it was. Nuclear weapons are the only natural or manmade disaster where the prevailing attitude in America seems to be "we can't ensure a 100% survival rate so it's pointless to take, or even suggest, protective actions to save anyone." It's like telling people "hey, there's no point in ducking if someone shoots at you because if they hit you point blank with that shotgun... you're dead." Okay, well that's asinine... what if they're not? If it sounds like I'm fired up, it's not your fault... it's just because I know exactly how and why this mentality came about and it pisses me off to no end.
Isn't the case that all the old fallout shelters everywhere are still good for the fallout? The physics of fallout haven't changed. Maybe the shelters need to stocked again with vital supplies, but underground is still underground. I have an extensive list of fallout shelters in my area from 1970. There was a big special supplement to the newspaper listing all the fallout shelters in the Kansas City metro area. Fascinating reading. Many of those buildings are still in existence. Someone here told me (I think it was CONELRAD) that the standard was a protection factor of 40 to be designated a fallout shelter.
Yes, they're still good from a shielding aspect. All that's missing are the government-provided supplies... so bring your own. Also keep in mind that the sign doesn't mean the shelter area is perfect protection. As you mentioned, it simply means the shelter area provides at least PF40 protection (reduces exposure by 40x). There can be unmarked buildings with even better protection.