Following the November 2015 “leak” of a classified slide purporting to show a Russian nuclear-armed and nuclear-powered drone intended to create long-lasting “zones of extensive radiological contamination,” both Russian and Western observers have suggested that Moscow may be developing a cobalt bomb. This conjectural device, which served as the basis of the “doomsday machine” in the classic 1964 film Dr. Strangelove, would employ radioactive cobalt to create unusually intense long-lived fallout. This article reviews the history and science of the cobalt bomb to assess the likelihood that Russia is developing such a weapon. It argues that while the lethality of the cobalt bomb compares unfavorably to that of “conventional” thermonuclear weapons, it might actually be a preferred means of creating long-lasting radioactive contamination because it could force an adversary to abandon territory while minimizing the number of immediate fatalities. But exploiting this principle in practice would be forbiddingly difficult because of the difficulty of predicting the ultimate distribution of the radioactive contamination, particularly for an underwater detonation like that envisioned for the “Status-6” drone seen in the Russian slide. While the underwater detonation of a massive cobalt or “conventional” nuclear weapon might create zones of long-lasting contamination, Russian decision makers would have little confidence that these areas would be in the intended locations, undermining the strategic case for such attacks. These findings suggest that the Kremlin is not pursuing radiological “doomsday bombs,” even though the nuclear-powered drone on the slide seems to be a real research project.