The Black Library contains the following documentation on the War for Semmiel:
Transmission from Techno-Magus Canabrea Adeptus Mechanicus Record AM533/2A4 Received Imperial Date: 2674444M41 Confirmation of the Necron threat on Semmiel, advising use of the Dread Legion, as our forces are now widely knowm.
Transmission from Battle Brother de Barres Adeptus Mechanicus Record AM843/6C7 Received Imperial Date: 4674445M41 Reports on our recent Battle for control of the desolate Hive Sable
Force Makeup Adeptus Mechanicus Record M243/5C1 Imperial Date: 4674442M41 Imperial record of the makeup of the Dread Legion, accurate at the time of departure from the Ares sector towards Semmiel.