Karlack's defenses

At the heart of the Crusade’s military power and the centre of the
Iron Collar that defends Imperial possession of the warp gate,
the fortress world’s perimeter is littered with defences. The first
layer of fortified space is a sphere of mechanised battle stations,
their augur arrays constantly scanning the void. A few track the
Angelus Invictus with their plasma batteries as it passes. Next,
on the outskirts of the occupied ring, are the massive space
docks where Adeptus Mechanicus adepts repair and slowly
construct new ships for the Imperial Navy. These jagged spires
and gargantuan platforms berth everything from gleaming new
fighters to the war-ravaged skeletons of cruisers who survived
battles their crews did not.
Supply stations, more advanced sensorium arrays, and voidfaring
troop barracks orbit closer to the faded greyish-green planet.
Karlack’s sky and atmosphere are thick with the smoke of industry
and clouds of dirt thrown up by the ongoing construction. Once
you clear the brackish cloud layer, the landmasses are patchworks
of bare earth, dull armoured fortifications, and the occasional
stretch of green farmland where fast-growing crop strains are
continually planted and harvested for processing into rations.
...
Tens of thousands of troops and transports stage from
Karlack at any one time, regiment upon regiment preparing
to replace the losses of an especially bloody battle in one
of the Crusade salients. However, in addition to the many
bases and emplacements in its orbit, the planet also requires a
large permanent garrison for defence and maintaining order.
Such troops occupy hundreds stations across Karlack, but the
largest, first, and most important of these is Citadel Primaris.
Citadel Primaris towers like a mountain above a plain of
levelled earth. Observation decks and weapon emplacements
jut from the sloping walls at regular intervals.

Deathwatch: The Emperor Protects