|Outcome||Ceasefire, Imperial withdrawal|
| Imperial Guard
Sons of Orar
After Dark Eldar raiders launched vicious assaults on Imperial shipping near the Craftworld, the Imperium, blaming the Craftworld Eldar instead of their dark kin, decided to make an example of Alaitoc by invading and annihilating it. The Imperium was able to trace Eldar raiding parties back to the Craftworld, identifying its location. Forewarned to the attack by the Craftworld's Farseers, the Eldar managed to prepare for the assault and were aided by the Phoenix Lords Baharroth, Maugan Ra, and Karandras.
The Imperium struck with an enormous fleet of Imperial Navy warships, carrying a large number of Imperial Guard ground troops. Battling through the Craftworld's fleet defenses in a bloody engagement that saw heavy Imperial Navy losses, the Eldar fleet and Craftworld defenses managed to destroy multiple Battleships and Troop Transports. However, Imperial Guard boarding parties managed to board Alaitoc itself. Though the assault by the Imperial Guard initially went poorly in the face of Alaitoc's Aspect Warriors, a Boarding Torpedo attack by the Sons of Orar Space Marine Chapter inflicted heavy losses on the Eldar defenders as the sheer number of Imperial Guardsmen managed to expand the Imperial beachhead on the Craftworld. Taking casualties in the face of the Space Marine spearhead and the Imperial Guard forces supporting them, the Eldar were forced to withdraw in order to defend Alaitoc's Infinity Circuit and core cities after the outlaying Exodite settlements were overrun and laid to waste. The Imperial assault was then slowed by the intervention of Phantom Titans and an Avatar of Khaine.
The battle for Alaitoc had become a bloody war of attrition, one in which the Imperium seemed to be slowly prevailing. Despite this and the continued Human advance, the Craftworld's Farseers foresaw ultimate victory for the Eldar. Nonetheless, the bloodshed continued as much of the Craftworld was laid to waste and even Titan war machines were destroyed by the Space Marine and Imperial Guard forces, while the dwindling Alaitoc's fleet continued to batter the Imperial Navy. The Space Marines, using their Chief Librarian to tap into one of the younger Eldar Farseer's minds, were able to accurately predict and counter Eldar strategies. Choke points and close-quarters fighting in the confines of the Craftworld worked in the numerically superior Imperium's favor and against the more precise and sparsely deployed Aspect Warriors. But despite these advantages, the Imperial forces took massive losses to advance across even fractions of the Craftworld's surface.
The decisive moment came when the Ranger Aradryan, who had discovered the real reason for the Craftworld's invasion before it had even begun, arrived on the Craftworld. Aradryan was able to convince the Sons of Orar Chapter Master that the attack had all been a ruse by the Dark Eldar. The Chapter Master, seeing that the entire purpose of the invasion had been for nothing and understanding to continue would see crippling losses for his Chapter, decided to abandon the siege of Alaitoc. With their Space Marine spearhead gone, the rest of the Imperial forces follow in the withdrawal. But while Alaitoc had survived the invasion, they had taken heavy losses and much damage to the Craftworld itself.