The invasion of Corticant: The alliance and the eldar

The alliance invasion of Corticant was comparatively unprepared and ill-equipped. The Tau and Federacy had no idea of the real importance of the device on Corticant and were oblivious to the multitude of forces now arrayed against the small world. It is likely that had they known such an invasion would not have been attempted at all.

The alliance force consisted of a small number of Cadres of Shadowstrike and Skyfall, with some support from Federal Hartak units (squats) and Alliance mechanicus from Vornax. This force prepared a landing zone in the north of the planet, with the intention of taking Fort Bastion and the planet's main communication hub, before mopping up resistance later.

Upon landing, the alliance forces were shocked to discover the world had also been invaded by the crusade, and the loyalists were already battling multiple Xenos. Unable to merely withdraw, the Mechanicum forces tried to hold off the Minotaurs, which they barely managed - Shadowstrike threatening the Crusade landing zone in order to take the pressure of the Ad Mech, who were losing badly. This worked, but the battered Mechanicum forces would play no part in the assault on Fort Bastion.

"Shadowstrike" (or most likely one of his disciples) then led the attack on the imperial capital, and the Federacy committed their own forces with the Squats of Hartak fighting as auxiliaries, teleporting into the Imperium's back lines to destroy their artillery effectively dirupting their communications. Despite the Imperium diverting all available forces to stop them they weathered the storm and captured the central refinery complex. This was key to the fort. Without power the forces of the imperium were doomed, but they did not surrender.

Gradually the Praetorian Guard were surrounded in the complex of Fort Bastion, bombarded by the Tau for hours, before finally trying to break out of the cordon and immediately being cut down. They did inflict significant losses on the Tau forces however, especially to their exposed infantry, but their armour and crisis suits were eventually able to push in, with Shadowstrike and his bodyguard personally forcing their way into the complex, destroying multiple armoured units before engaging the Guard in close quaters combat. They eventually relieved the beleaguered Squats who blunty swore they were in no need of rescue and had everything under control already thanks very much.

With Fort Bastion secure Skyfall's units made landfall and began moving the tau perimeter westwards, meeting little resistance, but by now the alliance did not know what to do. They had the capital but war had erupted all across the inhabited hemisphere of the planet. While they decided their next move, Skyfall's forces were attacked at Violetwind, forcing the tau to withdraw entirely to the Fort. Now, as the loyalist forces followed up, it was the alliance who were besieged at Fort Bastion.