The battle of Vervunhive (Gaunt's Ghosts "Necropolis") talks a lot about the defenses of a minor sized hive (probably only 500 million max).
I know that roughly 15% (at max) of the population was a part of the hive's PDF / Adeptus Arbites (75 Million) plus whatever Imperial Guard forces were stationed there.
I know that the void shields that the hive had prevented anything that the chaos forces attacking had, that said they did not have any planetary bombardment weaponry.
Once the enemy forces got inside, it was basically the equivalent of Stalingrad to the extreme.
Originally Posted by neilbatte
if you squint the Sigmar stuff doesn't all look like the love children from a Necron and Blood Angel orgy.