Horus remarked on several occasions that there were few challenges of war that could not be met by, or did not require, the use of such units. That's how you like the other Legions to think of you, isn't it? As the Imperial Warmaster, Horus took over command of the Great Crusade, and accepted his new duties with earnest dedication. These formations rarely had formal titles, but the Sons of Horus commonly referred to formations intended to prosecute a rapid assault as "Speartips.". , Horus' death broke the Sons of Horus' morale, and they were the first of the Traitor Legions to retreat from Terra, an act that would earn them the hatred of all the other Traitor Legions. The remaining portion of the Legion was betrayed and wiped out by their brothers on the world of Isstvan III, but not before reverting to the use of their original name, the Luna Wolves. After a fierce battle that saw the Warmaster slay Iacton Qruze, the Knights-Errant managed to escape. After smashing the Emperor's Children fortress and killing the clone of Horus, Abaddon declared himself the rightful successor of the Warmaster. The Dark Gods also revealed to Horus that the Emperor had once entered the Warp on the world of Molech millennia before and treated with the Ruinous Powers to gain the knowledge necessary to use the power of the Warp in the process of the Primarch's own creation. Even Horus, a generalist and a pragmatist, upon being given command of his Legion is thought to have adopted new squad formations after having seen their effectiveness in other Legions.
The warriors who fought these battles were of a character wholly in keeping with their reputation. This consisted of a group of Luna Wolves under the command of a Sergeant, though other titles such as "Chieftain" were sometimes used for senior Sergeants in command of multiple squads, harkening back to the leaders of Cthonia's kill-gangs. Their aggression was clear in their every action, but so was the strength of the control that held it in check, and the needs of that ancient age easily accommodated such a belligerent and cantankerous attitude. These 'recruits' were then taken to the geno-laboratories on Luna for the modification and indoctrination required to become Space Marines. Horus recovered in the Temple of the Serpent Lodge, a warrior and healing lodge on the planet. They have good attacking power, generally having solid damage, accuracy, and range, although a slow fire rate. I picked Thousand Sons because I've always thought their story was the most tragic. He developed a habit of partaking in local customs whenever bringing a new world into the Imperium, and the Luna Wolves were exposed to many such traditions as a result. If you invent the HIV vaccine, you have done a thing that is "good," like you want Loken's Luna Wolves to be. That is, to be truly loyal, Loken has to give up any future or glory for the "Luna Wolves," because that would mean accruing some kind of glory. After reading about the Luna Wolves and their fall during the Heresy, I like to imagine that there is still a few Loyalist Luna Wolves that serve the Emperor.