looking for battle brothers?

The Mech Marine chapter is a space marine army derived from the Iron Hands and are considerd rouge do to their anti-Imperium actions such as stealing titans, aquiring emperor class battle barges, and recruiting in the masses to defend their planetary system that has seemingly just entered the Milky Way.
The Mech Marines endevor to fight for a small freedom for the civillians that populate the five planets. They however are curious about the new arrival of these new planets which have appeared from nothing, Some speculate a warp storm swallowed the planets but nothing seems to be of demonic origin but the fifth world which also happens to be a death world appears to have catacombs of some sort. The Marines have not even dared delving deeper then what seems to be the first level out of thousands...