а как же их "фирменная усталость":
"?"The nature of siege warfare is long periods of dull, back-breaking labour broken by the most brutal, merciless combat imaginable. Men, even Space Marines, cannot withstand hell indefinitely and combat fatigue began to brutalise the Iron Warriors. The custom existed that once the siege lines were complete the besieged must either surrender or expect no quarter. With each campaign the Iron Warriors came to prefer the latter. Battle was to these Space Marines a release from the tedium of life in the siege trenches.
...
The Iron Warriors' indisputable success then led to them being 'typecast' to the extent that they became an automatic choice for a siege or garrison mission. But all troops need time for rest and reorganisation if they are to be at their best. Clearly some authority chose to keep the Iron Warriors in action despite the harm it was doing. The Emperor may have been deliberately testing Perturabo's faith but, given that Horus, as Warmaster, had control over the precise conduct of many campaigns, it is more likely that he was responsible