Forsaken Heresy

The Forsaken Heresy was a lamentable event in the history of the Hammer Guard Space Marine Chapter, when they fell into internecine fighting due to the corruption of the Chapter's 2nd Company, which spread their rot to several more elements within the Chapter.

History
Following the return of the Chapter's missing 5th Company and the corruption of the 2nd Company, for two years, the latter hid their heresy, leading the 5th Company into the same trap soon after the death of Legate Steelblade during the Drendix Crusade. They revealed themselves as the Chapter was united over Gabarlos, in a ceremony to honor the fallen Legate and appoint a new one. The Battle-Barge used by the 2nd and 5th Companies, the Vengeance of Sol, opened fire on the Hammer of Gabarlos then deployed it's forces to the surface of Gabarlos. The 3rd and 4th Companies immediately followed them as the Forsaken Hammers emerged from the warp, accompanied by a corrupted Solar Warden's Battle-Barge. The battle that followed would leave a schism in the chapter, the 2nd and 5th Companies managing to flee to the Maelstrom, their Forsaken allies capturing three Strike Cruisers as the Vindicta Solis was recaptured by the 1st Company, and the Solar Wardens coming to their progenitors aid and retaking their own battle-barge.