Black Slayer Clan
While much of the Ork Menace can be seen as like any other sentient fighting force, the Black Slayer Clan seem to challenge this. The last time this Clan had been spotted was during the assault on Armageddon, a Hive World to the Galactic Northeast. During the conflict, the Ork threat was so numerous that it required an entire brigade of the Steel Legion (Imperial Guard) and several companies from both the Black Templars and the Salamanders (Space Marines) to fight off that massive WAAAGH! of the Black Slayer Clan.
The Black Slayer Clan simply kills, destroys, and moves on. They do not take quarter. They do not take hostages. They do not take slaves. All of those actions are considered to undermine what it means to be an Ork, and the Black Slayer Clan holds all other Clans in contempt for choosing to use or rely on these practices. As such, any craft found should be destroyed or avoided at all costs.