Kull seem to be grouped into three rough castes: the ordinary Kull, the warrior caste, and the ruling caste.

Ordinary Kull are larger and more powerful than typical humans. They are also more resistant to hardship and pain. Such Kull will fight if attacked, and indeed makes up the bulk of the hive militia forces and the deck crews of Kull ships. They are no more immune to fear than veteran human troops and have been known to feel or surrender. Equipment is generally light; lasweapons and autoguns for the most part, a sort of perverse alien mirror of the IG.

Kull warriors stand nearly seven feet tall on average, and a much stronger and more durable than human soldiers. They also seem to lack many of the fear-responses so common in human soldiers, making them unlikely to surrender or break. Typically equipped with a heavy carapace suit and equipped either with a bolter or powerful lasweapon (hellgun). Although not individually as powerful as Marines (but clearly a match for the Daughters), these warriors must not be underestimated: they will stand and fight to the death, and are armed with weapons capable of killing even Astartes. The presence of large number of kull warriors (a typical cruiser might have as many as a thousand such warriors on board) makes clearing kulls ships a hazardous occupation at best.

Kull rulers are largely indistinguishable from the warrior caste, but always heavily augmented with cybernetics. In battle situations they are always armed in exoskeletal armour of varying potency. Many carry archaotech weapons that can kill Astates with impunity (plasma weapon, melta guns etc.). Thus far only a few have been encountered - colony commanders, high-ranking officers and the like. While individually powerful they lack the numbers required to be a real threat to Astartes.