Alright, I am very proud of the background for my custom chapter, the Sons of Gorgon. Criticisms needed. Tell me what you guys think!

Questions about it are also great.
*EDIT* Also, wall of text inbound.
Name: Sons of Gorgon
Allegiance: Imperium
Specialization: Siege Warfare
Home Planet: Poli-Aima
Current Chapter Master: Brutus
Current Strength: 800
The Sons of Gorgon are a Space Marine chapter derived from the Blood Angels. Their specialization in the tactics of siege warfare has lead them to the use of many heavy weapons. Their purity in fighting the forces of chaos and the orks is a credit to the imperium. However, they were not always like this. They were once known as the Hand of the Empire, and if it weren’t for a brush with near extinction, then their glories of the day would have never transpired.
Poli-Aima is a massive planet of rolling tundraa, frozen forests and sprawling forges. When the Hand of the Empire returned from a rather successful campaign against the orks, they were greeted with parades and much celebration, but the chapter master of the time, Ares, harbored a deep and dangerous secret. During the combat, his first company had discovered an ancient hammer locked away in a tomb deep in the planet. Ares demanded the hammer be brought to him, and soon he wielded it on the fields of battle. The hammer made the sound of thunder as it smashed through the orks, and the first company thought of this as a sign from the emperor of their imminent victory. But the hammer had other plans. This was no ordinary hammer, but a chaos artifact from the World Eaters Legion. The Hammer of Gore. It contained a daemon within who demanded to be in a constant soaking of blood. This was no problem during the campaign for the first company, who had itself repositioned to be on the front lines at all times. But soon, the hammer began to corrupt those in its presence. The 1st, 6th, 7th and 8th fell victim to its power. A rapidly increasing number of battle brothers were admitted to the Death Company from those companies, and at the campaigns end, more than 200 brothers had gone mad. Ares reported all 200 to have been killed, but he had really brought them abroad his flagship, the Imperial Hammer. Each company boarded their battlebarges and returned to Poli-Aima. Ares told the Captains of the 2nd through 5th companies, as well as the 9th and 10th companys, to go planet side while he remained in orbit to oversee the return of supplies. But no sooner had the last marine touched foot to the ground then droppods rained down. The Death Company, who had been fully corrupted to servants of Khorne, attacked the unaware companies. Captain Brutus of the 2nd company lead the defense of the planet, but they had been caught off guard, and were soon pushed back to Thait, the capitol of the planet. The local PDF was terrified, and as the armor of the traitors was very similar to that of the loyalists, had no idea who to shoot.
But before all hope was lost, a new fleet entered the system. Iron Hands 5th company, lead by the dreadnought Gorgon, was escorting Inquisitor Akito and his personal guard. What they thought was a peaceful Imperial planet had been turned into a warzone. The Iron Hands lead the countercharge into the traitors of the Hand of the Empire, while Akito regrouped with the loyal Companies. The traitors, in a desperate move, poured themselves onto the planet in hopes of spilling as much blood as they could. Captain Brutus, Inquisitor Akito and Venerable Dreadnought Gorgon defended the capitol for hours of constant fighting. At the climax of the battle, Ares revealed himself. He had ascended to full deamonhood, and was a terrible sight to see, the Hammer of Gore still in his claw. Gorgon and Brutus charged the deamon, who gleefully swung his hammer down onto Gorgon. Gorgon and Ares fought, but Gorgon’s steel was no match for Ares Hammer. Gorgon, seconds before the hammer crashed down on him, threw Brutus away, and detonated his still husk as to kill both the deamon and himself. Brutus, the new chapter master, released the Chapter from its bonds of heresy, and renamed it for the legend that had saved them from annihilation. For Gorgon was now their father, and they were his sons.
The Sons of Gorgon restrain themselves as to not fall to the madness that Ares lead them to. They keep their death company small and keep them in almost constant prayer so they may not slip to the dark gods. The prefer to kill their enemy at range so that they may keep themselves from succumbing to the Red thirst. They also continue to train their battle brothers in stealth, so that they may bring their fear of madness to the enemy. How can one concentrate if one keeps checking the shadows? The Sons of Gorgon are excellent at siege warfare, having a larger amount of vindicators and devastator squads then the normal chapter. Their geneseed is a combination of the blood angels and the iron hands, both founders of the chapter.
350 loyal marines survived the betrayal. The traitors fled and changed their armor to reflect that of the death company, but with the symbols of Khonre. The loyalists were reinforced with 50 marines from the Iron Hands, as well as a small supply of geneseed, as the Sons of Gorgons geneseed was in short supply. And so, at 400 marines strong, the Sons of Gorgon left on a crusade against the forces of chaos. Pursuing the traitors, the Sons found themselves in contact with Inquisitor Akito once again. This time however, Akito would be the one who needed saving. Land der Toten, a planet little significance, was experiencing a rather large uprising. An imperial scientist had developed a toxin that caused the host to gain increased physical abilities. The rebels worshiped him as "The master". The rebels goal was to enter a catacomb system under the capitol. Fearing more Chaos artifacts, Brutus lead the now 1st company into its depths, what they found was not chaos, but the control to a massive array hidden within the system. It was a well guarded secret of the inquisition. The inquisitor tasked The Sons to help cleanse the sector of its Chaos taint. And so began the Iris campaign, The Sons of Gorgons mission of retribution.