An Orion-class Battlestar that saw service in the Cylon War, the Osiris formed part of the infamous Ghost Fleet Offensive – a secret fleet hidden deep within Cylon territory, made up of Colonial ships that had been falsely reported destroyed in the early years of the war.

The Osiris met its end above the icy planet Djerba once a winter resort for human tourists had been captured by the Cylons many years prior, and became a crucial target for the Ghost Fleet Offensive. Left unable to fire its nuclear weapons after its launch doors were damaged, the Osiris elected to ram an enemy base star and then trigger its warheads manually, destroying both ships beyond recovery.