History

The Vortex Cannon was a powerful and technologically advanced weapon created by the Army, and used by the United Earth Government during the Alien Wars to wipe out one of the remaining alien strongholds on Earth. It was fired by General Phoenix against advice of its scientist creators, Dr. Banks and Dr. Steiner, and without consent of the President. While at first the cannon apparently did its job satisfactorily, it also accidentally tore a hole in the fabric of the space-time continuum as a side effect. This resulted in a time paradox splitting the original timeline, creating two parallel versions of Earth, one in which humans were wiped out instead of the aliens. It was thus needed to reconcile both worlds into the original timeline by merging the two Earths into one. The Damned City served as the intersection point/epicenter between these parallel worlds, with the dimensional gate serving as the portal between the two parallel Earths. Many of the Fiends that threatened the human-controlled Earth came through this portal.

Eventually, the Rogue Corps collapsed the dimensional gate, shutting down the Fiend's operations. What happened to the Vortex Cannon itself after serving its purpose is unknown. There is a strong suggestion it was destroyed in the aftermath of General Phoenix's lab explosion cover-up/"accident", the same explosion meant to kill Dr. Kurt Steiner and (supposedly) Dr. Claude Banks.

Gallery

Firing

An image appearing after the Vortex Cannon firing scene in both Rogue Corps motion comic #2 and in the game's opening cutscene.
This is presumably the aftermath of the cannon's power in which the alien lifeforms have been extinguished (represented by a large smoke cloud eerily shaped like Emperor Demon Gava).

Second aftermath image. Based on official artwork by Tony Washington.