The techmarines of the Iron Guardians had calculated the risks of deploying a mass assault on the by now completely hostile hive city and came to the conclusion that to fully defeat the traitors the hive city had to be cleared one section at a time to prevent overextension and ambushes. To do this numerous "Killteams" were created to split up the Astartes forces as they cleared the Hive room by room, the Kolusians also began doing the same thing as clearing individual houses with armored vehicles was rather difficult.
