[SunkenCiv]

In the 1970s a book came out, "The Fire Came By", in which this idea is fleshed out. It originated (if memory serves) in the 1950s, and has only been given credence because there's no buried hunk of asteroid in the crater (a Soviet sponsored expedition looked for it, repeatedly, starting about 20 years after the impact) -- something explained by Eugene Shoemaker et al in various impact crater studies -- and because the pre-impact sightings which survive from 1908 newspapers (from India, again, if memory serves) have a trajectory which could suggest a change of direction of the incoming object, IOW, that it was a vessel being piloted, rather than the natural object (of one type or other) that most people believe it was (including me).

[fire_eye]

One of the claims made in that book was that only a nuclear event could produce the ratio of radiant to mechanical energy produced by the Tunguska explosion - that chemical or mechanical processes are incapable of producing that much radiated energy vs. mechanical energy.