The Priory of Regret, also known as Covenant Special Operations 9 (CSO-9) was a Covenant Special Warfare unit formed and blessed by the High Prophet of Regret himself to aid in the Human-Covenant War. They participated in most of Regret's fleet's campaigns. At one point, they were assigned to aid an arbiter, Zhura 'Vakaree, in an ambush on a group of Spartans.