Deimos

Deimos is a forge world of the Ordo Malleus, formerly the outer moon of Mars, that now orbits Titan and supplies the Grey Knights with arms.

Deimos originated as the outer moon of Mars and was later developed into a forge world serving the Ordo Malleus. Concealed engines moved it into orbit over Titan. The relocation allowed the Grey Knights to be armed without disclosing Chapter secrets to Mars.

Knight houses and Skitarii continue to garrison the moon. Servitors, whose memories are wiped, carry out most of the transfers, which limits the information available to those who work there. Deimos thus remains the means by which the Grey Knights obtain their arms independently of Mars.