40k Lore, The Death Korps of Krieg!

The Goal of Every Citizen of Krieg is Sacrifice, for Only in Death Can The God Emperor Forgive the People of Krieg Their Sins.

99.8% casualty rate...
... And the 0.2% are apologizing for not dying just as they ran out of enemies to fight. They're currently driving around in three of the few remaining functional Chimeras and looking for anyone they may have missed.

What's a pyrrhic victory then, 99.9% casualty rate?
 Actually less than 99% casualty rate would be more considered lazy, pyrrhic victory implies that the victory is as bitter as defeat, where the resources made any gains not seem worth it. With the Death Korps of Krieg, that would either have a narrow error margin (as narrow as Rogal Dorn's tolerance towards deviations of his standards, which the cedar tree up his a***  represents in regards towards his distain towards that) or just not be in their vocabulary.

"Commissar, sir!"
"Speak Kriegsman..."
"We are ready to charge the enemy titans at once!"
"There's a titan out there?"
"Fifty of them actually... We'll charge immediately!"

Each Death Korps soldier is fully trained to the standards expected for combat-readiness set down by the Departmento Munitorum, with particular emphasis placed on hazardous-environment survival and endurance, and physical and mental resilience. Proficient in the use of all basic Imperial Guard weaponry types as well as the use of grenades and explosives, a Death Korps soldier is also proficient in rapid and skilled construction of trench works and defences. They are also exemplary hand-to-hand combatants, with bayonet-drill being practiced from childhood. Accuracy is secondary in Death Korps weapons training to fire discipline, with the ability to maintain continuous fire en masse as part of an infantry formation considered to be of paramount importance. Death Korps Guardsmen have a tendency to be highly insular, unemotional and often taciturn to the point of silence outside of their duties. They also display a high degree of fatalism and an unusual morbidity of habit, such as carrying relics, ossuaries of bone or other memento-mori about their persons as a form of religious observance to honour those who have fallen in the service of the God-Emperor. Spiked helmets are famously worn by the troops of the Death Korps of Krieg; however this is in truth rarely the case in the field, but many Krieg troops maintain the tradition either with improvised spikes or, less commonly, older patterns of the spiked helmet that have survived and been passed down through families (ie they still have family blood lines) The minds and characters of the young prospective Guardsmen are purposefully broken and remade stronger, just as their bodies are trained to withstand hardship and endure suffering that would kill other men -- a task already begun by the mere fact of living a life on blighted Krieg.

"You would laugh monster. But let me remind you. Within this weak sack of meat and bone, uncared for by his god and wept for by none, beats a heart. A human heart, that carries with it the strength and courage of all mankind. Within that sack of meat is the hope, the will, and the fury of every man women and child from every corner of the Imperium. Within that weak sack of meat, festooned in thin armour and weapons only powerful in numbers , beats the heart of a man. And for ten thousand years, the hearts of men have beaten, strongly, in defiance of your so called "powers". For ten thousand years, your black crusades have been pushed back, beaten down, and made a mockery of, by weak sacks of flesh with cheap weapons and disposable equipment. For that weak sack of flesh that you so gleefully mock is no supersoldier, no immortal warrior, no creature cursed by chaos like you. He is a man, an Imperial Gaurdsman drawn from some forgotten corner of the Imperium to fight for his species and for the safety of the people he loves. He is a factory worker. a farmer, a storekeeper, a father, a brother, a son, a mere man. And against creatures like you teeming and numberless, powered by the wills of thirsting gods...He holds the line. He has held the line for ten thousand years. So what is your excuse, monster?"