How did the C.C...? (late story spoilers)

[Oafish Philistine]

About two-thirds of the way through the story it is revealed most of the male personnel aboard the Cathedral have been replaced by C.C. doppelgangers--the telltale sign is that they bleed blue blood. There's a scene where Callaghan becomes suspicious about the behaviour of the other men and shoots his nerdy subordinate (I forget his name, the guy with the glasses) and he bleeds blue. How did the C.C. do this?
Speaking of Callaghan, why is he shoots himself as commanded by Circe but a C.C. impersonator version of himself later appears on the Cathedral?

[Aurora3500]

Full Spoilers

It is revealed later that Circe has the ability (granted to her from the 2nd capture by the Jewel Thief in Gaiden) to turn the male soldiers into C.C. that obey her commands.

It is done through intercourse with the male soldiers. So when they became C.C. their bodies regenerate from death. Essentially means Circe had intercourse with everyone who turned into a C.C. and bleeds blue blood throughout the past 9 years since the Cathedral had been built. Though they still emulated the behavior of their original host until the brain is shot. They regenerate, but anything that was part of the human original personality is killed. That's why Callaghan and the other soldiers act as puppets at the end. They regenerated and are now only C.C. that can follow orders without any of their previous human personality.

[Oafish Philistine]

That explains it. Thanks for answering my question!

[Oafish Philistine]

Come to think of it, if the C.C. "programming" only overwrites a male's personality after he is killed and regenerated, the male personnel becoming puppets becomes a plot element only after the climactic battle in August when the C.C. corpses attack the male barracks part of the Cathedral and presumably kill many of the men there.