Dark Calculation

The Dark Calculation was a near disastrous event that occurred during the ongoing Indomitus Crusade to the Sons of Galastram Space Marine Chapter when the Sons' flagship, Anvil of Valor was attacked in a surprise attack by their eternal foes - the Crow's Children Chaos Warband.

History
By the dawning of the 42nd Millennium, the Sons of Galastram had done well for themselves and earned honor and prestige for their bravery on the battlefields of Segmentum Obscurus, and were reconquering the Hive World Ciarra under occupation by the Black Legion. With most of the Chapter deployed on Ciarra to recapture the Hive Cities, the Crow's Children force of Plague Marines, revitalized under Peredrath the Ruiner's guidance, launched a surprise attack on the Sons of Galastram flagship, Anvil of Valor, and unleashed a viral plague into the Battle Barge's air filtration and rendered it uninhabitable, as well as slaying the wounded and token battle-brothers aboard the Anvil.

Crippled by this insidious strike, the Sons of Galastram's pride and honor were shattered, and there was a lingering doubt in the minds of the Chapter that the sacrifice of Aethelar Perro and his chosen elite marines to destroy the Dark Carrion, the Children's Space Hulk-turned Star Fortress, was made pointless as the Warband seemed to be flourishing regardless. But the current Lord Marshall, Drakor Karrios, dismissed these doubts by heroically capturing the capital Hive of Ciarra and led his Chapter on a hunt for the Plague Marines that humiliated them so.