the nuclear explosion effect

anyone have any idea how Tsuburaya pulled that one off? It's in my opinion the highlight of the movie.

I have a feeling what they did (at least for the beginning part of it) was shoot an upside-down city with an upside-down camera, and then blow fire up at it with a flame-thrower. As for the huge mushroom cloud- my guess would be that they set off a huge smoke bomb and just shot it in extreme slow motion from a really low angle?

Any ideas?

Also, I think Baragon's first two rampages are handled very well - when he attacks the oil refinery/ dockyards, and then later when he bursts out of the mountainside and smashes through the houses - the composite shots are excellent, with the people running around in the foreground.