Pala Olesis is the hidden homeworld of the Ronin. The planet's surface is 100% liquid, not including man-made settlements. All liquid on the planet is ammonia (NH3) instead of water (H2O), thus presenting the questions of how and why Mankind settled the planet.
Pala Olesis was settled sometime during the late Age of Progress by settlers sent out in later M3 in sleeper ships. The entire system was a checkpoint on the way to the Andromeda galaxy.
It was never rediscovered during the Great Crusade, and might not ever have been. It was by sheer accident that the Dawn Garrison (who would, upon review of texts in possession of the native inhabitants, rename themselves the Ronin) found it by sheer accident in late M32 after the 3rd Black Crusade.
The planet consists of large sprawling metropolis cities that prove labyrinthine even for those that never leave the planet. The highest are low rung and most are submerged. As the planet was initially settled by people born in M3, everything was independently developed from mankind outside the system, with only sleeper and generation ark ships coming in every few millennium to bring more people and technology before the Age of Strife.
Mankind was an ill-adapted species to live on a planet based on ammonia instead of water, but humanity has a fairly flexible gene-code and can adapt, especially when combined with some gene tailoring technology during the Dark Age of Technology, though it has been since lost. However, unlike most abhumans, you wouldn't know it unless you looked closely, where you would find iris-less eyes and skin with more yellow hues. And given that the only members that enter the Imperium proper are the Ronin, who believe taking off their helmets in combat the height of stupidity, discovery of this fact is unlikely.
Pala Olesis is governed by an seven member oligarchy. Each major quadrant of the planet elects a representative for life to lead. The fifth seat is held by the chapter master of the Ronin, sixth by the canoness of the Order of the Gilded Iris, and the seventh by the PDF General. This group must at least approve all the major decisions affecting the entire planet, but their main focus is on protecting the planet from any outside groups, especially considering the presence of a Webway Gate less than 50 light years away, that, though inert, could be theoretically activated at any time. The fact that one of the other planets in system is an inactivated Necron Tombworld is also a major concern, considering the usual defenses won't be as effective. They are fine letting smaller governments run things on a day-to-day level.
The Ronin are the first and toughest line of defense of Pala Olesis should it ever be discovered by an enemy. No enemy would make it through them unharmed, though they could very well make it through.
Order of the Gilded Iris
In present, the Order of the Gilded Iris, rebuilt from the few survivors the Ronin rescued functions more as an Order Hospitaller and Order Famulous than an Order Militant, though they have not forgotten their roots, and are more than willing to defend their new home of three millennia to their last dying breath.
Should an enemy get through both the Ronin and the Gilded Iris, the situation is dire. Any enemy looking to fight the PDF in the tunnels of Pala Olesis' cities is in for a difficult fight as they fight both in unfamiliar terrain, and with the knowledge that every valuable tunnel, chamber or room is at least partially submerged and can be sealed and flooded by the PDF if need be.
The greatest defense of Pala Olesis is how obscure its location is, with only its inhabitants knowing its location. And even if they did, the system is well over ten thousand light years outside the Milky Way, so their travel times would be large. Aside from that, it is a fortress world, with large amounts of defenses developed independently. Nearly all structures are submerged, with the tops of the highest buildings reaching perhaps a story or two at most above the surface, greatly hindering any orbital bombardment.