Here is some background on the regiment:
Vessen 409th 'The Stalkers'
Home world: Vessen Prime
Type: Agri/Hive (bordering on death world status)
Vessen Prime is an arid agri world with a single gigantic hive city - Prime One, breaking up the plains spewing pollutant gases into the air, this pollution coupled with its mildly toxic atmosphere leads to the inhabitants wearing respirators when not in the air locked hive city.
The arid plains of Vessen Prime are home to large predatory beasts and roving tribes of hunters and scavengers who shun the hive cities in favour of living on the move in armoured columns of hastily repaired and customized vehicles. These are the people that make up the armoured columns of the Vessen Imperial Guard. Having grown up in a life on the road the Vessen Imperial Guard are used to armoured warfare, as the hunters regularly come to conflict more often than not over some unique vehicle find. Most of the armoured hunting columns have access to old vehicles left over from the age of darkness, so when they join the ranks of the Imperial Guard they have some familiarity with the tanks gifted too them by the Adeptus Mechanicus.
The lifestyle on Vessen Prime has led the natives to be hardy of somewhat 'barbaric' in nature. But none can fault their record on campaign .
The 409th Regiment are nicknamed 'The Stalkers' for the way they conduct warfare. For an armoured regiment they go unusually long periods of time out of contact with high command hunting the enemy as they would the predatory creatures of their home world. The 409th have fought proactive and long campaigns against both the Tyranids and the tau. Both races have struggled with the unpredictability and variation from the normal Imperial Guard fighting style that the alien races have become accustomed too, making the 409th highly effective xenos hunters, which may be why the Inquisition has turned a blind eye to the incorporation of some xenos and non standard equipment into their armoured column.