Mantis Warriors

Mantis Warriors were one of the chapters guarding the Maelstrom warp storm in Ultima Segmentum. When the Astral Claws rebelled against the Imperium, the Mantis Warriors joined them cause they were allied for a long time and it seemed like a good opportunity for some ass-kicking. First they looted a [Fire Hawks]' ship, shattered the [Marines Errant] dispatchment, and only lost when every loyalist chapter ganged up on them.

300 Mantis Warriors survived. They have been granted Emp's pardon (since Astral Claws were corrupted by chaos, but no one knew about it) and sent on a 100 year penitent crusade during which they could not recruit new marines. Their worlds were given to Space Sharks, since the Sharks are crybabies and could not take the beating they got in the war like men.

Mantis Warriors are notable for being one of the few chapters who used camo patterns on their armor - during Tranquility campaign their armor had yellow and black tiger stripes pattern (the fuck, they were fighting on planets made of tigers, or what?).