The chaos force opposing them however comprised of unexpected forces. While the traitors fielded a number of knights, presumably supplied by Cybixx, the traitor astartes were not the Host of Eschar, Iron warriors, nor marines associated with the Emerald Serpent. In fact the marines had never been encountered in the sector. Apparently “Red Corsairs” but in the clear livery of the Alpha Legion, the Imperial Fists hardened their resolve to defeat these new enemies.
The push in the south did not start well. The Imperial Fists Typhon heavy tank quickly came under heavy assault from the chaos lines, as a heretical fellblade made its presence felt. On the chaos right, the alpha legion, equipped with rhinos, quickly made a move towards the imperial left flank, taking key objectives. With the traitor war dogs covering the chaos advance, the imperium were initially in deep trouble. The Typhon had been destroyed and on the Imperial right flank House Eagleclaw was under intense pressure from the traitor knights. The imperium had only made small gains all along the front and defeat here risked the entire imperial positions on the west portion of Mordecai Tersius.
The Imperial Fists now advanced on foot, converging on the centre of the battle. The Alpha Legion were surrounded and crushed in brutal hand to hand fighting, stabilising the front line, but the Fellblade remained a potent force. The knight duel on the imperial right saw the loss of knights on both sides, but the imperial war engines failed to make headway towards the Helverins. By the end of the first day the risk of imperial collapse had been halted, but the southern push had barely penetrated a few tens of kilometres into the chaos defences, and after grinding their way to Lake Peri, the southern assault was called off.