The first thing the 18th did when it arrived on Medusa V was to secure The Khan Defense Complex in Hive Sybilla Primus, as soon as they moved in they made contact with what Col. Neils Moergant (CO of the 74th Cadian Grenadier Regiment) call "Blasphemous Traitors". It was clear to the Col. that the traitor guardsman where supported by Chaos Space Marines and they where more powerful then normal Marines (although I leave that judgment up to you). The timely arrival of The Sisters of The Midnight Watch and The Black Templares saved the 74th from being lost. As word of the battle made its way to the ears of soldier’s in the 18th, the name of one of the most Dammed Traitor Fabius Bile. Almost at once the Regimental Commissars where order to kill anyone who spoke that name.
But at 0530hrs. The 48th Infantry Regiment's FOB was attacked by Traitor Marines and it was conformed that Fabius Bile was with them. The soldiers that lived where taken by Inquisitor Hera and never seen again. It would fall to the Black Templars (who had lost a number of warriors to Bile's forces) and The Sisters of The Midnight Watch to purify Bile's debase warriors. +++++++++++++++++All Files On Fabius Bile and Actives on Medusa V Sealed, By Order of Inquisitor Hera+++++++++++++++++++++++++++++++++++++++++++++++
General Victor deBougogne Ray XVI was not one for fighting defensive wars, so he went to Hive Euryales and meet with Lord Marshal Harazahn and outlined his plan too conduct a counter-offensive in Battle Zone Hydra. After being shot down in the Ash Wastes and having to be rescued by the newly reformed 48th Regiment. At 0430hrs The Counter-Offensive round Sybilla Primus; Code Named Operation Roundhammer begin. In less then three hours, the Chaos forces were eliminated and much of the Khan Defense Complex retaken. And the enemy pushed from the Hive City into the Underhive.
Now with the success of Operation Roundhammer, General deBougogne Ray XVI begin planning Operation Roundhammer II, this Operation would see the 18th Take Geryon Base and then make two main attacks, one Northwards towards Hydra's Tooth and one due east into the Geryon Strip Mines.
The Operation Roundhammer II went awry from the start, the enemy force was larger then Intel. has estimated and almost as soon as the 18th tired to push into the Geryon Strip Mines they were forced back. At Raffaello's Spine the 18th launched massed assaults on strategic targets, forcing the Black Legion onto a retreat from their mountain positions. The battle in the Spine was to go back and fore of many days, before the 10th could clear the passes in the North and start moving towards Ice Station Alpha.
It was a good thing too, that it had taken so long because as the 18th start to head for the station the Tau dropped the asteroid called "The Hammer" on the Station. With the Stations destruction the Black Legion attacked withdrawing 18th, in 74th Regiment all the men and women of Alpha Company decided to sacrifice themselves to show down the enemy so the rest could withdraw. All but Col. Moergant died facing the dreaded Black Death armored company. The 18th had to fight a number of Breakouts and Rearguard actions before they made there way the Hell's Crucible.
There they reinforced the Guard and Space Marine forces fighting there, and was even able to conduct small attacks into the Ash Wastes destroying a set of Bunker and killing two self-styled Warlords.
But as the final weeks came, the main mission of deBourgogne Ray XVI came back to the forefront to get as many citizens off the world to fight in Cadia. To that end deBourgogne Ray XVI did something that many Medusa V PDF commanders still hate him for to this day. He ordered the 1001st Medusa V PDF into the line and then withdrew his Guards and made his way to Geryon Base (although a number of officers have tired to change Ray with treason, he is too powerful for anyone but the Inquisition to make any changes hold). The 18th then conducted of defensive war around Geryon Base as the citizens of the world were transported to Cadia. They created over fifty kilometers of discrete earthworks, so well-hidden that when the 18th left Medusa V the enemy didn't even know they where gone.
General Victor deBourgogne Ray XVI returned to Cadia with over 3,000,000 personal to be put into the fight for Cadia. Ray had a chest full of medals and to mark his great victory he was given Lady Julia Strophes of Scintilla as his wife. But for all the great fan fair the cost was high over 90% casualties, it would take years and a re-founding of Regiments before the 18th was really of war again.