Daedalus was first established sometime during the Age of Strife by several Explorator Arks sent from Mars to establish new Forge Worlds. House Van Dyre also joined the Exploratory vessels in an attempt to reclaim their lost glory. The Arks came across Metion - a Gas Giant and it's largest moon - Daedalus. The relatively small planet took the Explorators interest and they began settling and building up the barren world. With the insurmountable experience of the Mechanicus and help from House Van Dyre, who set up on a nearby lush world of Sanct-Solum, the moon quickly became a prominent industry world of the Imperium.
Daedalus soon established itself as one of the dominant forces in Argus Sector and began building their armies in the form of their own Skitarii Legions and a Titan Legion. The Mechanicus made contact with nearby Hive Worlds and established trade routes as well as defensive alliances with the Noble Houses of these Hive Worlds.
Due to its location close to a Gas Giant, an Agri-World and access to several mining and factory worlds, Daedalus became the centre of industry and arms manufacturing of the entire Argus Sector.
Ork Invasion 404.M41
Some years before the Macharian Heresy, Argus Sector began suffering from large scale Ork raids to the point where a single Imperial world could not hold against one of the greenskin raids. In response to this Daedalus sent out most of their Titan and Skitarii forces to assist and reinforce allied Imperial Hive Worlds in order to protect the Agri-Worlds and Mining-Worlds so crucial to the Mechanicus continued existence.
In a surprising show of cunning a large Ork fleet showed up near Daedalus, hell-bent on salvaging the massive treasure chest that is a Forge-World. Half of the Ork ships made to the surface in full speed and disembarked their forces, at least the ones that didn't ram the planet full speed. The invading Orks proved to be a great challenge to the Mechanicus as the greenskins slithered through the mechanical jungle like a plague of rats, slaughtering and destroying anything they came across. Salvation came in the form of Blood Wights Space Marine Chapter, as they arrived to aid their Mechanicus allies in their time of need. Methodically herding and hunting down the planet-side Orks, most of Daedalus soon managed to return to normal. The remaining greenskin fleet was about to be caught off guard by the returning Daedalus fleets. In a last hurrah their Ork captain ordered the fleet to ram the ships into the Resource Pipes stretching from Daedalus to Metion, in result destroying 8 of the 20 facilities and causing immense damage to planets industry as well as burning out 0.3% of the Gas Giants precious resources.
At first Daedalus was considered a Dead World, but its location and resources within its core proved reason enough for the Mechanicus to settle the inhospitable planet. Prior to the construction of Mechanicus facilities the surface of the planet was that of a grey and brown wasteland with occasional craters and rock formations, all open to the outer space due to the non-existing atmosphere.
As the Mechanicus began building up the planet it changed drastically throughout the millenia. The massive sprawling mines were dug deep within the planets core when the surface of the world had all but layers of metal stretching across, holding up the massive factories and spires of the Mechanicus. Now the planet is more reminiscent of a giant man-made globe rather than the barren world it once was - a testimony of Omnissiahs might and his followers ingenuity. Upon landing on the planet it resembles a giant metallic bee-hive with no recognizable ground level. Traversing the planet on foot is nigh-impossible as the spires and buildings are only intertwined by cables, pipes and small walkways. One wrong step and a curious visitor will go tumbling down into one of the mines within the bellows of the planet.
Another ingenious marvel are a dozen massive tubes stretching from Daedalus to its parent Gas Giant - Metion. With a radius of up to half a mile these constructs are used to siphon precious gas and other resources back and forth between the two planets, or transport personnel and equipment without employing space-faring vessels. Each tube ending on Metion is its own full fledged Mechanicus facility used as a base of operations for the resource gathering on the Gas Giant.