War of Survival
The War of Survival was a major event in the history of Valhalla.
In M30, as Valhalla faced severe food shortages, another major threat appeared: a fleet of damaged Ork space ships had been cast through the warp to the ice world. The Orks descended on the planet and proceeded to fight the Valhallans for the food they had stored. They held out bravely for a long time in their sub-glacial cities but were pushed back to the food vats. The battle looked hopeless for the humans, but the defenders held out long enough for Valhallan engineers to use their ice-boring machines to bore through the ground beneath the Orks. The tide was turned as the fiery ice-melting machines ran amok among the Orks, burning and terrifying the Orks. The Valhallans took the offensive and cut down any Ork which had not been burned or melted.
Ever since the siege, the Valhallans, particularly their sons and daughters enlisted in the Imperial Guard, have hated the Orks more than any other xenos race, and become especially adept at fighting them on other worlds throughout the Imperium.