Pyrathas' defenses

In a galaxy plagued with oddities and anomalies, Pyrathas nevertheless deserves mention. Although ignored by the humans of the ancient Jericho Sector, this world was set to become a lynchpin in the Iron Collar and a vital resource to the Acheros Salient.

Pyrathas was discovered almost by accident, in the second year of the Crusade. As the Crusade fleets advanced into what would become the Iron Collar, Explorator ships ranged ahead, cataloguing new worlds for conquest. When the frigate Omnissiah’s Dispatch dropped out of warp on the edges of System Designate 018-9J0-5B, they found a system dominated by a fierce blue-white supergiant star. The fury of the star’s heat had long ago blasted every planet to half-molten cinders - save one. An immense jovian world, Pyrathas Majorus (itself a smouldering brown dwarf star) whipped around the supergiant in a tidally locked orbit. Tucked safely in its penumbra, a single moon was likewise tidally locked, heated by the embers of its planet, and containing a breathable atmosphere. The captain decided to investigate.

The moon that would become known as Pyrathas was a harsh, inhospitable place. Low gravity had created a world of towering cliffs, high mountains, and deep fjords. The constant gravitational stresses generated massive volcanoes, leaving the atmosphere a gray haze, and life had not evolved past hardy lichens and mosses. At first glance, Pyrathas had nothing useful to offer the Crusade. However, Lord Militant Achilus and his staff saw an opportunity in Pyrathas - a shielded anchorage, protected by the fury of its sun, and ideally placed between the fortress-worlds of Karlack and Hethgard.

On Achilus’ command, Pyrathas became the latest link in the rapidly forming Iron Collar. The rough terrain proved ideally suited for fortifications. Legions of Munitorium convict-labourers capped the mountains with adamantium bastions and dug extensive launch bays for Lightning and Thunderbolt fighters into the cliffs. In areas of active vulcanism, they sank deep geothermal shunts to power concealed defence laser batteries. Meanwhile, the Mechanicus constructed large orbital docks around the moon to service the needs of the myriad warships that would soon come. In one short decade, Pyrathas was the second largest anchorage for the Imperial Navy, surpassed only by Karlack itself.

Unlike the majority of the other fortress-worlds, the Navy took some pains to conceal Pyrathas’ exact location from its adversaries. Pyrathas’ coordinates are considered a Magenta level secret, and the signs and counter-signs to enter gun range are only possessed by the pilots of system defence monitors who wait on the edges of the star system to escort arriving vessels. Of course, the Navy realised it could not maintain Pyrathas’ location as a secret forever, and also installed scores of orbital laser and torpedo batteries.
In the years since, Pyrathas has become a valuable fortress
in the Iron Collar. When the Orpheus Salient succeeded
well beyond the Crusade’s plans, Pyrathas served as a transit
centre for Guard regiments and military supplies retasked
to the nearby Acheros Salient. Then, when the tendrils of
Hive Fleet Dagon began to curl around the Crusade forces
in the Orpheus Salient, Pyrathas saw its role reappraised. It
remained a transit centre, but the flow of men and materials
reversed to staunch the dangers of Dagon.
Certain Crusade commanders (Pyrathas’ Captain
Skor among them) have privately voiced the opinion
that should the Tyranid hive fleet defeat the Crusade
and consume the Jericho Reach, Pyrathas may prove
a final refuge against the swarm. The furious glare of
the blue supergiant makes approaching the anchorage
without the protection of void shields suicidal, and thus
far the Tyranid hive ships encountered do not have a
suitable alternative.
...
Pyrathas’ primary orbital installation, Adamant Station looms over the moon like a vast, ironwork spiderweb. Adamant is an orbital warehouse, the void-dock for dozens of ships at any one time. Stretching many hundreds of kilometers across the sky, this mid-orbit installation is so large that it is easily visible from the surface.

Scores of defence laser batteries comprise the outermost sections of Adamant Station, linked together with massive adamantium chains and straining grav-links. Together, these stations provide an interlinking field of lance fire covering many of the approaches to the station - with free-orbiting batteries on the far side of the moon defending against the rest.
Further inward, the station becomes a maze of docking
bays, loading stations, and orbital cargo vaults. These facilities
allow the flow of vital supplies between two Crusade salients.
Naval anchorages are segregated from the transport docks,
though most of the Navy warships prefer independent orbital
anchorages high above Adamant.
The centre of the station hosts its command basilica, as well
as vast gaping launch bays for flights of Furies, Starhawks,
and other attack craft. In the centre is a massive orbital tower,
capable of ferrying large quantities of men and supplies to the
surface installations.
...
And the fortification built on the planet below the above orbital stations? Even larger. All in 10 years, and on a hellhole of a planet.
Even so, the installations on Pyrathas have grown to an
impressive size, even larger than Adamant Station above it.
Scattered along the rocky cliffs of one of Pyrathas’ larger oceans,
the fortifications have been dubbed Fortress Illium, and they
have capped the cliffs and ridges in steel and adamantium.
Illium is centred around the base of the orbital tower that
links it to Adamant Station. Through it flows a constant torrent
of supplies and Imperial Guardsmen—the former destined for
the vast supply caverns cut into the bedrock below the base,
the latter to wait inside the labyrinthine stretches of barracks
surrounding the central bastion.
Most of Illium’s installations—supply caverns, barracks,
sustenance processors, hab-farms, laboritoriums, medicae
facilities, repair and maintenance depots, and even a small
forge maintained by the Adeptus Mechanicus—exist
within the miles of caverns carved under the surface. The
population of a major city lives, works, and prepares to
fight under the ground.
Above their heads, thousands of kilometres of trenches,
bastions, fortifications, walls, and razor wire stretch out from
the central bastion. Every sector has overlapping artillery
emplacements, supported by shorter ranged mortar positions
and buttressed with air defence emplacements. Every cliff along
the ocean has hangers cut into the very rock for Thunderbolt,
Lightning, and Marauder aircraft.
- Deathwatch: The Jericho Reach