The Cerberus is assimilated by the Bydo.

R-13A Cerberus

Once he was a fearless hero, now a forest watchdog. What evil keeps him leashed here?
~ R-Museum Epitaph

The R-13 Cerberus is one of the fighters in the R-Type series. In R-Type Delta, it is one of the three playable fighters, this ship was sent to investigate the Bydo Seed Incident in 2164 and near the end of the game, when it tries to escape the Bydo forest, it is captured by the Bydo and later assimilated and the communication ceased just as the mission was completed. Space Corps (The Millitary) never made an announcement about the loss. It later returns in R-Type Final as both a secret boss and an unlockable fighter. An RX-12 Cross The Rubicon has sent and explore the bydo forest Stage 3.5 and tries to rescue the assimilated R-13 but they both ended up in a fought beacuse the R-13 was being corrupeted by Bydo. The R-13 gets destroyed by the end of the stage!