Battle of Aquila Atoll
Before the battle began, the forces of Ultramar arrived on Zarathusa Secundus, to defeat the Dark Mechanicum enclaves on the loyalist Ocean World. They successfully did so and then returned to their island base, Aquila Atoll, to await extraction from the loyalist fleet in orbit. However unbeknownst to them, a Dark Mechanicum fleet had arrived and destroyed the loyalist fleet, before sending drop ships containing Legio Mordaxis to Zarathusa. This led the forces of Legio Lysanda, the Knights of House Vornherr and divisions of the Imperial Army, to be caught by surprise when they spotted Mordaxis' emblems on the quickly descending drop ships. Soon the infected Titans began to advance upon the Atoll, causing the toxic oil Mordaxis was infected with, to spread across Zarathusa's oceans. This liquid infected anything it came across and a group of Vornherr's Knights fell under its curse, during the battle.
After seeing this, the Loyalist forces began to retreat from island, with Legio Lysanda's Titans leaving behind any of their allies who could not keep up. Knowing that they could not escape, Legio Mordaxis did not pursue the Loyalists at first and instead began destroying the Atoll. Lysanda's commander, Princeps Tesarius Solomere Krane, meanwhile did not know the loyalist fleet was destroyed and his forces kept trying to contact it. With no response to their communications, Krane ordered his forces to continuously retreat, as Legio Mordaxis pursued them across Zarathusa. Weeks later, Mordaxis' Dark Mechanicum masters, grew tired of the chase and tricked the Loyalists into thinking their fleet had returned for them. Not knowing the truth, Krane brought his remaining forces to a Deepfleet drilling station and awaited an extraction to safety. Soon, though, a large number of Legio Mordaxis' Titans appeared and overwhelmed the Loyalists, destroying or infecting them; just as they had done to large swatches of Zarathusa's surface.