I'm thinking "they" have been working on this for Quite Some Time Now, probably since shortly after they found the group of Fog ships including Kongo and Maya. They wanted more Fog ships, they didn't know about the repair base at Midway, and along comes someone with an Idea both terrible and genius. Abyssal!Fubuki may have been operational for some time before Corwin's attempt to fabricate a new body for I-401. (At the end of The Human Experience Clemson suggests that it hasn't been long, but he might just mean that they're only just now done testing the revenant.)

What I think Corwin did do is create some sort of metaphysical link between Fog ships and their templates, or enhance one that was already there by virtue of the hermetic law of similarity (witness Lionfish). In other words, I think the extended edition of Fubuki's dying-dream is Corwin's fault, but not the fact of Abyssal!Fubuki's existence.

(As pointed out elsethread, we don't really expect Earthgov to get into the occult, but that doesn't mean someone in research and development isn't dabbling in it. Or perhaps the mysterious Russians from "just after the Great Patriotic War", or at this point probably their descendants, have sold Earthgov on a scheme that includes rather more sorcery than they're letting on. Someone developed that control spell, after all, though how they managed to hang any kind of magic off that jumble of unconnected nouns is beyond my understanding of such things. That was a nice touch, incidentally, clever way to amp up the creepiness.)