I've never seen anybody prior to the previous decade that has advocated such a patently stupid theory. Obviously as a result, this violates the 30 year rule on here, but let me take a moment to try and historicize this from what I've seen both of the history of nuclear weapons, conspiracy theories, and my interactions (few though they have been, thank goodness) with these modern cranks.

Nuclear weapons were born out of secrecy and kept it shrouded around them. Vacuums of information allow all manner of imaginative speculations to run wild. One of my favorite examples of this from the Manhattan Project was a rumor that Oak Ridge, where uranium was enriched, was actually a secret experiment run by Eleanor Roosevelt of what a perfect Communist utopia would look like. (Though quite wrong, there are shades of truth here: Oak Ridge was a totally government-run, government-planned community. But not by Eleanor, and not for the purpose of Communism.)

Most of the speculative, conspiracy aspects about nuclear weapons in the Cold War concerned things like spies, secret machinations, shadowy motivations, things like that. The closest you can get to "the nukes don't exist" were concerns that "the nukes won't work" — this was because of the limits of truly testing what nuclear war might look like, because you generally cannot do a "full system test" (e.g. a mated missile + warhead + realistic trajectory) without risking said war itself. (Donald MacKenzie has written much on this in his wonderful Inventing Accuracy.)

I have not seen any examples where people, during the Cold War, asserted the weapons couldn't work at all and were just a hoax. Why not? For one thing, it's dumb under any circumstances. What are the odds that every scientist, in every nation in the world is going to be in on this hoax? By itself this makes it pretty dubious. And before you suggest, "but maybe not every scientist..." — atmospheric nuclear testing, which was common before the 1960s, releases detectable fallout particles globally. A trained radiochemist or physicist can easily distinguish between a bomb reaction and a reactor accident (or reactor by-products). What this means is, the monitoring of testing of multi-megaton weapons was something quite easily done by lots of people, even everyday folks. So even if you want to somehow believe that all other forms of evidence (witness testimony, the clouds that reporters were able to photograph, even the blinding light that could be witnessed by millions who lived around the Nevada Test Site) was somehow just all "part of the conspiracy," you'd have to assume that not a single scientist — not one! — looked at the fallout and said, "oh, this is all just made up."

You have to be a special brand of high-grade conspiracy theorist to even think this is a viable way to waste your time. Which brings us to the present. What motivates these people? They ultimately appear to derive from one retired engineer who has fundamentally misunderstood neutron cross-sections (sigh) as implying that fast fission reactions (e.g., those that take place in bombs) cannot occur (he thinks slow fission reactions, the sort that take place in reactors, are OK). From this misunderstanding (which is just technical enough to confuse or fool laymen into thinking it is clever), he decided that rather than his understanding being possibly in the wrong (sigh), everything else must be a lie, and so he and his followers have pulled together a very dumb theory.

Much of it rests on sheer misunderstanding (they like to assert things like "production of pure energy isn't possible" — as if it isn't laid out, very clearly in every technical text on the subject, the ways in which the energy from nuclear reactions is partitioned into heat, blast, radiation). The most interesting (from a historical standpoint) misunderstanding is based on parallels drawn between firebombing and atomic bombing. Emphasizing the similarity between the two has been a major way in which the morality of the atomic bombing has been adjudicated: e.g., often as an argument of, "well if the firebombing was acceptable as a form of warfare, then why couldn't the atomic bombs be?" There's a lot one can unpack there, but it's kind of amusing (if it isn't so stupid) that the conspiracy theorists jump from "there are some moral similarities based on some phenomenological similarities" to "the atomic bombings were really just firebombings." (Never mind that there are major phenomenological differences between the two, as well — they are only superficially similar because they involve mass fires. Never mind that there were hundreds of thousands of survivors to the atomic bombings who could attest that they were not raided by the hundreds of planes required to create that kind of firestorm, or that saw the single plane with its single bomb and its blinding light, or so on. Never mind how this theory treats victims of the bomb as being "in on the conspiracy" in a way that moves beyond the dumb and into the insulting.) It's interesting to me, as a historian, that this moral argument got re-tooled into a conspiracy argument.

Now, I suspect this retired engineer or whatever he is is perhaps just genuinely confused and has worked his way into a cognitive or epistemological corner. (He also thinks the Apollo moon landings were a hoax as an aside.) The real question is: why does anyone listen to this obvious nonsense? I've interacted with a few of them, and read their writings (more than I care to, to be honest), and the basic "profile" I have for most of them is that they're already conspiracy theorists and they are looking to out-conspiracy the other conspiracy theorists (they seem to take pride in the fact that they are considered "out there" by people who think that the moon landings were faked, that 9/11 was an inside job, etc. etc.). They seem to be people who appreciate the theory for its audaciousness and challenge. This strikes me as a very late-20th century/early 21st-century sort of peculiarity, a similar motivation that is sometimes expressed (much less attributed-to) the Flat Earthers (as one of the Flat Earthers explains in a recent Netflix documentary, he saw Flat Earth as "the last conspiracy theory on the shelf" — wait until he stumbles on the nuke one!).

Though they cloak their interest in some kind of traditional politics (e.g., they say the hoax was concocted in order to maintain huge expenditures on military resources and fear to control the public, etc.), I get the sense that they don't really care about any of that. They certainly aren't in it for "truth" or anything like that. They ignore any arguments that contradict them. They aren't that smart, and they aren't that technical, though they pretend to be. They are occasionally anti-Semetic but that seems to be an argument of last resort ("have you noticed how many Jews were involved with the Manhattan Project...?") and not the overall motivating force. Ultimately I think this is about them feeling clever and superior, including more clever and superior than their fellow "theorists." They are subpar conspiracy theorists, as an aside: they are not getting the "best and brightest" to sign on to this theory, probably because their total numbers are very small from what I can tell (whereas, for example, the 9/11 theorists do have a substantial number of engineers who can actually engage in technical arguments, however misguided, these guys really cannot), and perhaps because the technical arguments are so misguided that anyone with any real technical competency avoids it.

And, of course, the real overall historical thread here is: these are people so alienated from the realities of nuclear weapons, some 70+ years after they were invented, that they can pretend they don't exist. It takes a really different world than the postwar, the Cold War, even the immediate post-Cold War, to take that kind of cognitive stance. I am inclined to see it as a side-effect of an overall alienation from the weapons that we see quite broadly (and my quantitative social scientist colleagues have studied) at the present moment, where you have an entire generation (or two) that has not been taught to worry about them, and now — when they appear to once again be returning to our consciousness — is trying to reconcile themselves with them.

But anyway. I've never seen any evidence of anyone claiming the bombs were all just a hoax in the past. It's entirely possible and probable that a few fringe people thought such a thing. They weren't given an infinite megaphone (like the Internet), however, so who knows. I see this current little subculture (which again is very small from what I can tell) as being a product of Internet-born conspiracy theories (and the "arms race" for these people to seem more clever than one another) mixed with a post-post-Cold War alienation-and-rediscovery of The Bomb.