The 5th Legion was formed in January 2553. Their original purpose was meant to be used as a secret military police that would patrol the galaxy searching for Chat conspirators. However, the intentions of legion were forever altered after the destruction of the Chat Star and a Resistance victory over Havin IV. They began to be used in combat in order to take down influental members of the Resistance without expending a mass amount of Chat forces.
They first appeared during the Attack on Dark Oculus, though they were unsuccessful in protecting Bravadostock or Spartan A-118. They would also appear during the Chat's assault on Beta Maximus 35b, this time assisting and protecting Haloprov. Later on, a lone legionnaire would attempt to kill Uvok on the streets of New Haven during a Resistance attack. However, the legionnaire ceased his lightning attack after the arrival of the Grand Centurion. For unknown reasons, the Grand Centurion murdered this legionnaire. He then ordered Darktroopers to bring Uvok into a Chat Shuttle and take him to a prison on Moris for interrogation. Another one also got into a fight with Megan, though he was killed by here after a lengthy battle.
Each legionnaire of the 5th Legion is permitted the use of up to two white or orange bladed laser cutlasses. Along with that, they are given two smoke grenades, a yellow armored uniform, and a single flash bomb used to temporarily blind targets. They are also trained in hand to hand combat and in the use of firearms, though they rarely use these fighting styles in combat.