The home world of the Crimson Fists chapter is Rynn's World. It was invaded by the Ork warlord Snagrod, the Arch-Arsonist of Charadon and the Crimson Fists defended it, ultimately defending and saving New Rynn City from being over-run.
More famously, this battle is noted for being the original front cover of Rogue Trader itself. And within the halls of Warhammer World, this very scene has been reproduced.
The diorama is compact, but very detailed. The core of the Crimson Fists are set up so that when viewed from the side, it replicates the front cover of Rogue Trader very nicely. The wider fields of view show the wider battle scene with wrecked vehicles and Orks and their contraptions moving in for the kill.