004-006.M31 Battle of Signus Prime - The bulk of the Blood Angels Legion was despatched to the distant Signus Cluster by the Warmaster Horus to put down a local uprising. Knowing the IX Legion will never join his cause and fearing their Primarch as an impediment to his plans, or worse, a rival for the affection of the Ruinous Powers, Horus sets his trap at Signus Prime, where in 005.M31 the Blood Angels are beset by a foe none have ever faced before, the daemonic legions of the Ruinous Powers, and assailed by terrifying psychic assaults and distortions of reality. Reality bends and the fabric of the universe is torn open by the powers unleashed by the Warmaster.
005.M31 Jorgall Execution - The Jorgall campaign was carried out during the Great Crusade against a race of humanoid aliens known as the Jorgall. Many of these xenos featured extensive cybernetic physical enhancements to improve their physical forms and enhance their fighting abilities. Elements of the Sisters of Silence, alongside the 1st, 2nd and 7th Great Companies of the Death Guard with Mortarion as the commander, launched an assault into the main Jorgall cylinder world in the Iota Horologii System. The Astartes penetrated the drive cluster and destroyed the xenos' control of the cylinder world's motive power centre. Battle-Captain Nathaniel Garro, alongside an elite cadre from the Sisters of Silence, neutralised the construct's hatcheries. Following their hard-fought victory, there were dissenting voices from the Mechanicum contingent who petitioned Mortarion for a few days in which to loot the alien craft of technology. The Primarch, as was his prerogative, refused the request, as the letter of Malcador the Sigillite's orders -- and therefore, by extension, those of the Emperor Himself -- was that the Jorgall incursion into the sector was to be exterminated and nothing more.
005.M31 Battle of Isstvan Extremis - The elite 1st Company of the Emperor's Children Legion fought in concert with the Death Guard Legion's 7th Battle-Company, under the command of Battle-Captain Nathaniel Garro, against traitorous forces on Isstvan Extremis, the outermost planet within the Isstvan System. Whilst fighting against a powerful Slaaneshi psyker known as a Warsinger, Garro sustained serious injuries; crushing damage to his torso and arm as well as the loss of his right leg from the mid-thigh down. He was only saved from certain death by the timely ministrations of the Emperor's Children's Chief Apothecary Fabius. Taking stock of the desperate situation, the Emperor's Children Lord Commander Eidolon made use of a hitherto unknown ability -- a modified tracheal implant bonded with the lord commander's vocal chords, that allowed him to produce a nerve-paralysing shriek similar to that employed by certain warrior breeds of the reptilian xenos Laer. This powerful ability killed the Warsinger and helped the Astartes carry the day, but was indicative of the Chaos corruption already rapidly consuming the III Legion in the days just before the outbreak of the Horus Heresy at the Isstvan III Atrocity.