The WEAPONS were supposedly made by the Ancients as a countermeasure against the Calamity. The Ultima WEAPON most likely reacted to the Calamity's awakening.

[He pauses, thinking back.]

In fact, as I recall, we heard the WEAPON right when the Calamity started spreading, didn't we?

[Come to think of it, it's been almost a year now since their assault on the facility. Things have only become more and more complicated...]