The Imperials knew they had to cross the hilled desert regions and regroup to a new defensive position further north on the plains in front of the hive city. Imperial high command was hopeful they could stop Stygian forces from capturing the hive but only if Imperial forces pulled back quickly enough. Furthermore the resulting tactical withdrawal would shorten the decimated supply line and put the ground forces under the umbrella of friendly air cover.
The retreat turned out to be a bloody affair. Stygian militia blocked some of the passes. There under the protection of sand bagged dug in positions they opened up on approaching Imperial forces. Imperial forces under pressure to hustle to a new rallying point were temporarily stopped and often times strafed until they could form up and take the positions by storm. most times the militia would retreat after inflicting what casualties as they could then come back at night when parts of the Imperial forces were through the strong point, and reoccupy the position and force the same confrontation on the other half of the Imperial force.
Nights on the march also grew to be trying for Imperil forces. Such was the pace demanded by high command that Imperial troops would spend over half the night on the march catching only a few hours rest. It was an endurance test that saw those that failed left behind to be picked off by pursuing stygian guard units. Worse during the night marches the risk of ambush was far greater. Furthermore some of the stygian militia were devotees of the cult of Khorne. During the night they would use the darkness to close with retreating Imperial columns then launch devastating surprise charges into the imperials midst. Their axes an chainswords causing carnage as they wantonly butchered all they could before being cut down. Those militia units that did this were always annihilated but never before inflicting a disproportionate amount of casualties and weakening Imperial morale. After all the devotees of Khorne knew that the blood god cared not from where the blood flowed, only that it flowed.
Another blow to Imperial morale came as they marched past supply depots and outposts. These Imperial command had ordered destroyed in order to deny their use to the Stygian Empire. Marching past Imperial outposts burning fueled the sense of doom and defeat on imperial regiments. At long last they reached the new defensive lines an occupied them in preparation for the onslaught they all felt sure was coming. They had suffered on average 30% casualties on the march but they had reached relative safety now and so with grim determination they waited.
Asura the Alpha legion commander in charge had no intention however of launching an all out assault on the new imperial line and storming the hive. He knew with the bloody attrition that city fighting brought about that he lacked the strength at the moment to take the hive. Accordingly he established a new line and switched over to the defensive. Operation Nesting Asps had negated the Imperial numerical advantage, forestalled an imperial offensive, and allowed him to take valuable ground vital for creating multiple defensive layers on advantageous terrain. Furthermore the disproportionate casualties accrued during Operation Nesting Asps now left him slightly outnumbering the Imperials. With the operation having achieved it's objectives Asura ordered the construction of new defensive strongpoints in a defense in depth and awaited the next strategic development in the north and shifted his attention south where the Stygian offensive was proceeding although at a reduced pace.