Ketsu-Go ("Decisive" Operation) was put into place by the Japanese military in April 1945. It was a general name the Japanese used for their plans for what to do regarding an American invasion. Rather than trying to stop the invasion at the beach (which they understood would not work), or to let the Americans gain some kind of foothold (which would be hard to dislodge), they wanted to split the difference and try and destroy whatever beachheads the US would try to establish a few miles inland of their landing, especially in Kyushu (the southernmost Japanese large island) and the Kanto plain around Tokyo. This would involve "special" tokko tactics — suicide attacks — on land as well as the by-then normal "special" attacks with airplanes and boats (kamikaze).

Part of this effort was the National Resistance Program, where all able-bodied civilians would be trained to attack Americans in guerrilla operations. A defining feature of Ketsu-Go as a whole, which the National Resistance Program also embodies, is the bet on extracting a high cost in blood against the Americans using quantity rather than quality. With a high-enough cost, the Japanese military leaders reasoned, the US might be likely to accept an end to the war on terms that would be more favorable to the Japanese than unconditional surrender.

Prior to Ketsu-Go, in March 1945, the Japanese government had already passed several laws that would allow the instant conscription of Japanese civilians, both for the construction of fortifications, but also as part of a Patriotic Citizens Fighting Corps that would put the civilians under military control in the event of emergency.

So it is a little confusing, because Ketsu-Go is actually their whole defense plan, but only the National Resistance Program part of it is what people usually mean when they reference it. Additionally, Ketsu-Go itself evolved considerably over the course of 1945, and didn't really embody one singular plan but a lot of efforts directed at the same outcomes. Most of the details about the Ketsu-Go program that exist in the historical literature are about the logistics of the military side of the planning, not about civilians wielding sharpened sticks. The most likely impacts of Ketsu-Go would have been Japanese plans to use waves of kamikazes against American bases, which would have been unsustainable but intense for a short while.

So some Japanese civilians were definitely drilled/trained for hand-to-hand urban combat. Using that as a justification for Hiroshima and Nagasaki, however, is a stretch. There is no evidence it factored into any of the decision-making; quite a lot of the arguments in favor of the bombs are based on ahistorical myths, like the idea that they were only dropped as an alternative to invasion (the plan was to bomb and invade), or the idea that it is clear that the atomic bombings are even what caused the Japanese to surrender (versus, say, the Soviet declaration of war and invasion of Manchuria, which also threatened the Ketsu-Go strategy by promising a much larger invasion against an enemy who did not have as much imagined intolerance for bloodshed as the Americans). Like many arguments to justify the bombing, it also hinges on the idea that noncombatants are valid military targets — a disturbing and dangerous idea that we should be highly dubious of (and would today be considered the clear road to war crimes).

One way I like to suggest Americans in particular think about this is how the language of "fanaticism" is used to "Other" the civilians in Japan. If you were talking about Americans defending themselves against an invading power, would be talked about heroically, not as some kind of "fanaticism." How many American films are about civilians fighting back against invasions of some kind? How many American films laud the person who stays behind to commit suicide in a way that will take out the enemy? These are all tropes that, when applied to an "Other," we see as evidence of their evilness, "fanaticism," etc., but when the roles are switched we see them as heroic, patriotic, natural, etc. The Japanese military and civilians saw the Americans as foreign invaders, not liberators.

None of this excuses the horrors the Japanese military enacted against civilians in the Pacific nations they invaded and occupied, of course. But I am very dubious about using this kind of Othering to justify the use of weapons against civilian populations. It also distracts from the actual issues that went into the planning and use of the atomic bombs, and implies a false dichotomy — two atomic bombs in three days, versus every Japanese civilian throwing themselves at (trained, well-armed, able-bodied) American soldiers. The realities of the end of the war are a lot more complex than this sort of thing. It is not surprising to me that Wikipedia in particular is lacking in detail on this; it is common for things on this topic. A while back, I did a big overhaul of their Operation PX article, which is about a biological weapons attack plan the Japanese had, which also is frequently cited as a "justification" for the atomic bombs. The original article, which had been plainly used as the source in many "derivative" stories about the operation, did not make clear that the Japanese themselves had cancelled the plan almost as soon as it had been made, a rather important detail, and that under no circumstances, with or without the atomic bomb, would it have been carried out! This is the kind of disingenuous history that does real damage to how people think about the atomic bombings, which are also the "template" the Americans use for thinking about whether "the ends justify the means" in war, and so there are really important stakes in getting this stuff even somewhat right.

Anyway. The source that has the most details about Ketsu-Go (which, again, only has the civilian operations as just one part of it) is Richard Frank, Downfall: The End of the Imperial Japanese Empire (Penguin, 2001). Frank accepts a little too uncritically that the atomic bombs were necessary, effective, etc., but to be fair, the book came out 20 years ago (the strongest argument for the role of the Soviet invasion mattering at least as much, or more, than the atomic bombs didn't come out until 2005), and his book is more about describing the Japanese planning and American invasion plans than it is the American atomic bomb history (which was largely a separate-but-parallel thing, because of the secrecy and compartmentalization associated with the Manhattan Project).