Black Legion - Specialist Ranks and Formations: The Mournival - The Mournival were Horus' most trusted advisors and confidants. Consisting of four chosen Captains of the Legion, the Mournival existed outside the rest of the XVIth Legion's regular command structure. Together the Mournival functioned as the soul of the Luna Wolves, and later the Sons of Horus, supporting their Primarch and steering the Legion's temperament and decisions. The Mournival had many important responsibilities, which included making sure that the Legion and its Primarch lived up to their standards of moral excellence and the Emperor's vision of the Imperial Truth in prosecuting its duties and helping the Primarch devise strategies for more effectively carrying forth the Great Crusade. The Mournival on occasion even provided Horus the means to posture politically as a means to save face or present a certain united front when in the presence of the XVIth Legion's Imperial allies and enemies alike. Horus relied on the Mournival to balance his decisions with questions and different perspectives. In this way the four Captains served as a combination of counsellors, confidants and naysmiths. It is known that there was an element of ritual to the bond between the Mournival brothers: meetings of the Mournival took place in moonlight, a different phase of the moon was graven on the helm of each brother, and its oaths of brotherhood were made over the reflected image of a moon. The origins of the Mournival are unclear, although there are parallels with the rites of brotherhood amongst the Jutigran clans of Terra and the ritual practice of the Selenar gene-cults of Luna, who were integral to the early integration of many Cthonian Neophytes into the XVIth Legion. Whatever the Mournival's origins, its existence within the Legion certainly lies in in the early decades of the Luna Wolves' history, and it is known to have persisted for a time even after the Istvaan III Atrocity, though by then it had lost any meaningful check upon the actions of Horus and continued to exist solely due to tradition. The last members of the Mournival before the XVIth Legion fell to Chaos included Captain Horus "Little Horus" Aximand (Half Moon), First Captain Ezekyle Abaddon (Full Moon), Captain Garviel Loken (New Moon) and Captain Tarik Torgaddon (Gibbous Moon).Justaerin Terminator Squads - The Justaerin Terminator Squads were one of two distinct sub-formations found within the XVIth Legion's elite 1st Company. Led by the Legion's First Captain, the black-armoured Justaerin were the pride of the XVIth Legion. Tasked with forming the "point of the spear" of the Legion, they went where the fighting was thickest, their attack directed usually at destroying the heart of an opposing target or conducting the decapitation strike of an enemy force. Early proponents of the use of Tactical Dreadnought Armour, many of the Justaerin entered combat as Terminators, relying on the resilience this gave them to smash aside any resistance and close in for the kill.Catulan Reaver Assault Squads - The Catulan Reaver Assault Squads were the other sub-formation present in the XVIth Legion's elite 1st Company. They too, sported the signature black armour which denoted their specialisation in harrowing actions and hit-and-run tactics. They were led by a Captain under the overall command of the Legion and the 1st Company's commanding First Captain. They also made extensive use of Terminator Armour, taking advantage of its additional protection and ability to smash aside any opposition. Used in combination, these two elite sub-formations of the 1st Company exemplified Horus' predilection for precise and overwhelming attacks against strategic targets.Reaver Attack Squads - Reaver Attack Squads were an evolution of the Despoiler and Assault Squads found in the order of battle of the Luna Wolves, epitomising in many ways the Sons of Horus' way of warfare. Heavily influenced by the tactics of the seething and incessant tribal warfare of Cthonia, Reaver units specialised in lightning-swift assaults which maimed and disabled a foe, striking down leaders, mercilessly cutting down any who were weak or isolated, and sowing panic and disorder in any who remained.Despoiler Squads - The Tactical Squads known as Despoiler Squads were designed to be held in reserve and unleashed once a weakness in an enemy line had been identified. Trained in fire saturation techniques and carrying additional close combat weaponry for use in overrunning enemy positions, the so-called Despoiler Squads showed the dominance of the Tactical Squad in Horus' tactical thinking. Such was the effectiveness of this tactic that its use was copied in several different Legions.Destroyer Squads - Considered dishonourable by some Legions who made little use of them or eschewed them altogether, Destroyers were equipped with and expert in the use of otherwise proscribed and forbidden weaponry. Alongside certain factions of the Adeptus Mechanicus, only Destroyer cadres had the license to use these weapons in the forces of the Imperium by the Emperor's command. Rad-weapons, bio-alchem munitions and the burning horror of Phosphex were amongst the forbidden weapons in a Destroyer Squad's dark arsenal, weapons which irrevocably tainted the ground upon which they were used. Marked by their fire-blackened and chem-scalded armour, Destroyers were often shunned and deemed somehow tainted by their fellow Battle-Brothers in many Legions and were considered at best a necessary evil, although the effectiveness of their relic-weapons in cracking especially difficult enemy defences could not be denied.Seeker Squads - Seeker Squads were comprised of a specialised force of Space Marines whose principal task on the battlefield was to identify an enemy's command structure, its warlords, officers, priests, demagogues, whatever form they took, and slay them with a well-placed bolt round while the battle raged round them. The Alpha Legion is said to have first crystallised the use of this tactic and squad configuration, which had with the Emperor's approval spread to the other Legions, although its use sat poorly within the combat doctrine and martial culture of some like the Space Wolves. Equipped with special issue ammunition to assist their efforts, Seeker Squads were primarily composed of the finest shots within the Legion, as a Seeker strike force often only had a small window of opportunity to take down its targets at close range, rather than enjoying the luxury of distance.28th Armoured Assault Company ("The Back Breakers") - During the Warmaster's invasion of the Coronid Deeps, the armoured formations of the Sons of Horus were deployed across multiple war zones. In particular, the 28th Armoured Assault Company (known by the informal cognomen of the "Back Breakers" for their use as a heavy assault attrition unit) claimed battle honours at Lascal and Tara canis, broken up into smaller, ship-based battlegroups, before taking part en masse in the final destruction of Hive Ilium on Manachea. In this conflict, the Sons of Horus deployed an enormous range and variety of armoured formations, maintaining a fluid command structure that allowed them to operate as a highly mobile reserve capable of reinforcing successful breakthroughs and delivering the final, crushing blow to a collapsing enemy defence. In particular, as the bulk of the Legion committed to the assault on Hive Ilium penetrated the hive city's dense environs, it split fluidly into multiple smaller strike groups. Each of these was assigned a squadron of tanks or an individual super-heavy tank to force a way through the heavier choke points and city nexuses, crushing defended positions and engaging enemy armour even as the Sons of Horus infantry counter-attacked any enemy that attempted to outflank the war engines and bring melta weaponry to bear. At some point during the Great Scouring, the 28th Armoured Assault Company ceased to exist in its established form, but from its remnants the Sarissan Iron Pact arose. This Renegade Warband is still heavily mechanised and consists of Spartan Assault Tanks, Land Raiders and a small number of Land Raider Achilles. Much of their infantry consists of Chaos Terminators.Luperci - The Luperci (or "Brothers of the Wolf" in Cthonian) was a special formation of Sons of Horus that consisted of Possessed Chaos Space Marines. Formed with the assistance of the Word Bearers, the Luperci were essentially a mirror formation of the Word Bearers' formation of the Gal Vorbak possessed Chaos Space Marines. The Luperci were created following the events of the Dropsite Massacre on Istvaan V, and were first deployed during the Battle of Molech.