The first strike was delivered by the Apocalypse Riders. Their elite formation targeted the enemy's best troops and the overall commander of Na'Porkleon's forces in the north. Led by their chapter master, the bikers rode into battle, challenging the orks to come out and fight. The greenskins of course accepted.
At the vanguard the astartes best led the way, but initially suffered from an immediate counter charge by the ork warboss, who hacked his way through several elite bikers, bellowing challenges to the Riders' leader. Instead of accepting, the chapter master disengaged, leaving his comrades to battle to the death with the ork meganobz. At the end of the fight only the warboss remained as the imperial raiding force opened fire with everything they had.
The ploy had been simple, to get the best of the ork forces out into the open, and it had largely worked. The astartes mourned the loss of their brothers, but the chapter master knew this was their best chance to decapitate the ork force in the north, and now the rest of the two armies were engaging. Relying on their skill and flamer weaponry, the heavily outnumbered marines took the fight to the greenskins, causing carnage in the ork ranks. Land speeders added long range firepower and fast moving scout forces took the orks by surprise, outflanking the loota positions and breaking the ork lines.
The Blood Axe warboss remained alive however, having weathered an impossible storm of fire from the Apocalypse riders. Smashing through the wreckage and corpses of his comrades, the giant ork eventually found his foe, the Apocalypse Riders' leader. Finally the ork had the mighty human warrior in single combat, but the fight was brutally short. Both combatants wielded incredibly powerful melee weapons, and in a few scant seconds both lay in a pool of blood and gore on the now silent battlefield. A few remaining orks in the retinue had fled, but the ork leadership had been destroyed. Na'Porkleon's armies in West Coast now had no one to direct them. Van Dorn's second phase began.
The Adeptus Mechanicus units pushed south towards Berkeley, encountering fierce ork resistance on several occasions. The greenskins were uncoordinated in their attacks, and the Mechanicus forces engineered situations to their tactical advantage, preying on the ork need for battle by deploying in defensive positions and waiting for the orks to run into pre-determined killing zones. After each slaughter the imperial forces moved forward, and by 1211.013M42 much of West Coast was once again in imperial hands, and the coast of the Sump Sea was in sight. Berkeley was still infested by orks and Na'Porkleon had sent a new warboss to the region, but the line had been stabilised.