Gal Vorbak - Battle of Calth: As the Horus Heresy unfolded, Lorgar ordered his subordinates Erebus and Kor Phaeron to strike a vital blow against their most hated rivals, the XIIIth Legion, the Ultramarines. Unknown to Erebus or Kor Phaeron, their Primarch had a secret objective in mind when he had sent his two most zealous sons to launch a surprise assault on the Ultramarines' world of Calth. Lorgar's most trusted servants were more than willing to gain the chance for vengeance upon the Word Bearers' hated foes, pinning the enemy forces down in the Realm of Ultramar while the main forces of the Traitor Legions advanced on Terra under the command of Horus.After their humiliation at Khur, thousands of World Bearers within the XVIIth Legion detested the Ultramarines. The Urizen ordered a great gathering of his Legion while their fleet was already en route to Calth. The Primarch called for Argel Tal, the leader of the Gal Vorbak, and one other Word Bearer officer. These two loyal sons would eventually become commanders and apostles amongst the elite of the Vakrah Jal. The Primarch wanted their counsel on what to do with those amongst their Legion he no longer trusted.The Word Bearers had culled their ranks down through the solar decades, removing such unrepentantly Loyalist elements as the Terran-born warriors of their Legion, but had carried out no purge like the Istvaan III Atrocity that the World Eaters' Primarch Angron was so proud of. Lorgar knew that the loyalty of his own Legion to both him and his vision of Mankind transformed through an embrace of Chaos was never in doubt, but competence was another matter entirely. Lorgar asked what should be done with those warriors of the XVIIth Legion he felt were no longer reliable; those whose hatred burned brighter than their sense.For tens of thousands of them -- whole companies, whole Chapters -- their rage was no longer pure. It was decided that these suspect elements of the XVIIth Legion would be gathered into a single host and ordered to undertake the "sacred" mission to Calth to assault the Ultramarines that they had so craved. They were led by Erebus and Kor Phaeron and were expected to martyr themselves in glory. The other Traitor Legions such as the Emperor's Children, Sons of Horus and the World Eaters might have purged their own ranks at Istvaan III, but the Word Bearers proceeded to purge their own during the Battle of Calth.Thousands of the Gal Vorbak were left to die, alone and unsupported, on the surface of the devastated world of Calth when First Chaplain Erebus fled the conflict that the Word Bearers had fought against the Ultramarines on that benighted world. These Word Bearers had been left to die. They would never be reinforced. They would never be recovered. All those Gal Vorbak who spent months of their lives fasting, praying, scarring their flesh in preparation for a chance to taste the Divine Blood, were lost.Argel Tal was the sole surviving original member of the Gal Vorbak, having been seconded to the World Eaters Legion for temporary duty before the Word Bearers' assault on Calth. Argel Tal forsook his oaths to the annihilated Serrated Sun Chapter and gained permission from his Primarch Lorgar to form a newly constituted formation, known as the Vakrah Jal, the "Chapter of Consecrated Iron", who rose from the ashes of those Word Bearers companies devastated on the killing fields of Istvaan V. Argel Tal gathered hundreds of leaderless Astartes and gave them unity and new purpose.