Ferrus chose the fastest of the Legion's ships, and together with his most veteran troops, sped towards Istvaan V ahead of the rest of the Legion. As they had feared, the majority of the fleet arrived too late to take part in the attack, and it was with dread and horror that they learnt of the disastrous treachery that had greeted their Primarch's attack. He and the Veterans joined with six other Legions in the planetary assault. Ferrus spearheaded the attack with two other Legions, suffering horrendous casualties as they dropped into the planet's atmosphere. The four Legions that were backing up the initial attack turned on the unprotected flank of the loyalists in an unforeseen betrayal, sealing the doom of the Legions, who were massacred in the ensuing battle.