A field test for the first thousand sets of Space Marines equipped with Mk VI Power Armour (provisionally dubbed the Mk V at the time, as the armour that eventually bore that designation had not yet been developed), the campaign was waged against the Eldar of the Scalland Sector. Raven Guard forces were chosen to conduct the operation despite their recent heavy losses in the Akum-Sothos Cluster. There is some speculation that certain Imperial commanders led by Perturabo pushed for the under-strength and bloodied Raven Guard to conduct the field tests in hopes of their failure and thus the cancellation the Mk VI project, which Perturabo hoped would spur the development of a new heavy assault variant in its place.
However if that was Perturabo's intent, the plan backfired as the Raven Guard performed admirably against the Eldar forces. They used their advanced auto-senses and increased agility to hound the Eldar in a series of hit-and-run attacks. Originally just intended as a field test, the Raven Guard were actually able to expel the Eldar from the Sector altogether. As a result of their success, the Mk VI armour was approved for mass production. In the Raven Guard's Primarch Corax's honour, it was dubbed Corvus Armour.