A ruthless reputation: Lying for morale purposes
Deception was a key part of warfare. Every general Frederick had ever fought knew that, excepting perhaps one particular necron. This deception, however was different. He was lying to his own troops.
Billions of brave, loyal soldiers manned the outer defences. Most of the population of Hvelgelmir, fighting as militia to defend their homes, enough Midgardian guardsmen to populate a small sector, regiments and armies from dozens of world's all fought like cornered beasts against the endless devouring tide.
In the opening stages of the engagement Frederick deployed his crack troops to handle breaches, defeats, places where deploying normal soldiers would be little more than putting meat into a grinder. His Helguard, Astartes and legions of power armoured infantrymen could clog that grinder.
He knew his elite forces could only be spread so thin and that he would need their unmatched skill at arms later, for when the devourering swarm hounds at the walls of the Hvelgelmir Prime Fortress. He knows they must retreat.
...
At Mamcunium Hive, sitting high on the hill it is named after, the devourer was pushing hard. The tunnels and passageways under the hive became a hunting ground for the genestealer, fast, and almost invisible, a perfect killing machine; provided it could slip past the perimeter. Given the perimeter was full scale war, and on some fronts the humans were losing, thousands of the chitinous beasts managed to avoid detection and make it through breaches and weakpoints; holes in the net guarding the hive.
Suddenly the "safe", "secure" area behind the walls was akin to a nightmare, haunted by monsters you could hardly hope to see before they tore you apart.
To fight these creatures required lighting fast speed, utter immunity to fear, and the coordination of soldiers with a hundred years fighting in each others company. Five black irons regiments were deployed, along with significant telepathica elements.
The rear lines of the hive saw these few thousands of soldiers save millions. Avernite reactions, trained by decades in the Bush caught and gunned down leaping clawing monsters. Battle psykers stared into the shadow, looking for the moments slip that would reveal their enemies.
They were doing well, perhaps even winning. The regulars topside were holding, and the infiltration problem was improving. The soldiers knew this wasn't an unwinnable battle, they felt like they were genuinely making gains.
Then the order came for the elites to pull out. Casualties had reached a point where defending this region was no longer tenable. The idea was to retreat and fight another day, before the hive was entirely cut off. At least, for the Avernites.
The regulars on the other hand were given the most imperial of orders. "No retreat. Not one step back. We fight and die here. The line must hold. Reinforcements are coming."
The Avernites unhappily retreated, a dejected silence filling the dropships that took them to the next front. The hive, without it's back lines guarded, fell within the day. No survivors.
As the last guardsman died, the black irons were already fighting to hold another fortress, the people of Mamcunium nothing more than another sad memory amongst the many those soldiers held.
...
Frederick hated lying to the men under his command. He thought it was ugly, and avoided it whenever it was possible. He also knew that his soldiers were not Avernites. They would fight harder, for longer if they believed that they can win.
He told them help was coming when it was retreating. He told them to hold a line he had condemned hours ago. He let them believe that if they fought hard enough they might survive.
Sometimes he wondered if he deserved his reputation.
@Durin