The Dulma'lin Cleansing was a year-long campaign fought by the Catachan II regiment under the command of Colonel "Iron Hand" Straken in 926.M41. It was fought primarily in the Ork-infested cavern network of the planet, where the Catachans used guerrilla tactics to wreak havoc amongst the Orks.
At one point Straken's men became the target of their own ambushes, slain by a seemingly cunning and stealthy Ork in the Warboss Killzkar's employ. The infamous Ork Kommando, Snikrot, engaged Straken in a brutal dual, and was eventually defeated and grievously injured.
The climax of the campaign was the infiltration of the primary Ork settlement in the Mommothian Vault by Straken and his demolition experts. They managed to stay undetected for three solar days before the Orks' Squighounds finally located them. By then it was too late as the Catachans had planted explosives on the cavern's support stacks, while Straken himself fought off the Ork horde, killing no less then 30 and wiping out a Killa Kan mob before dragging the Warlord Killzkar beneath a Squiggoth, who trampled them both.
Incredibly, the demolition team managed to pull Straken's body from the cavern before it collapsed, destroying the entire Ork settlement beneath. The Catachan hero Sly Marbo personally carried Straken to safety. The Colonel was patched back together with the aid of Astra Militarum medics and he was redeployed to the Ulani System with his regiment, while the High Praetor Osh'preen arrived two solar days later with Imperial reinforcements and easily finished off the now-leaderless Ork horde, taking all the credit for himself and becoming the world's Planetary Governor. Osh'preen later declared that the Catachans were cowards who had hidden for the duration of the campaign. Despite the governor's slander, a statue of Straken was erected by those citizens who remained both loyal and thankful for the Catachans' aid.
Two standard years later, the increasingly corrupt reign of Governor Osh'preen opened the way for a heretical uprising by the Slaaneshi Cult of Frantic Flensing. The Catachan II were the only regiment close enough to offer assistance but due to a "mysterious" series of communication failures that bedeviled the Catachans, Osh'preen and his corrupt government were left to their remarkably horrible fate.
- Codex: Astra Militarum (6th Edition) (Digital Edition), pp. 75, 366
- Codex: Imperial Guard (5th Edition), pg. 23
- White Dwarf 357 (AU/NZ), pg. 71
- Straken (Novel) by Toby Frost