Unlike most other Covenant rankings, "Ossoona" was a temporary rank bestowed by the Prophets of the Covenant upon specially selected Elite warriors, making it comparable to the typical rank of the Arbiter.
Due to a lack of intelligence on the United Nations Space Command, the Prophets had begun to pull a handful of Elites from active duty into temporary service as Ossoonas. To be chosen, an Elite must have already had the rank of Elite Major. This is because the higher ranking Elites are "worth" more in active duty, whereas the lower ranking Elite Minors were considered too untested and liable to either become easily compromised; or abandon their mission in pursuit of their own personal glory.
The mission of an Ossoona was to collect information on the enemy while avoiding any type of combat. Many of those Elites felt that there was little honor in such an assignment, but they would do as they were told, due to their reverence of the Prophets. Covenant leaders felt that zeal was a quality to be admired, but an espionage job would help tame young Elites and teach them the finer arts of stealth in battle.
The title of Ossoona was usually bestowed for a single mission, though a series of missions were sometimes given. An Ossoona would always be equipped with Active Camouflage generators and devices similar to UNSC Helmet Recorders. They were usually equipped with a Plasma Pistol and Plasma Grenades as well as energy shielding just in case an Ossoona was discovered. Ossoona missions would tend to include non-combat intelligence gathering, such as capturing high ranking enemy personnel, equipment, AIs, weapons, etc.
Because many Elites were reckless and tended to destroy everything in their path, the Prophets (Hoping to learn more about the Humans, including the location of Earth) sent 'Nosolee on a special mission to gather intelligence. Even though he was killed when Captain Keyes shot him in the head with a M6D Pistol, the attendance of the Ossoona in the life pod Captain Keyes had fled aboard alerted the Covenant to his importance, and ensured that they captured him instead of killing him along with his party.
|Temporary/Prominent||Ossoona • Arbiter|
|Fleet Commander||Fleet Master • Supreme Commander • Imperial Admiral|
|Zealot Officers||Field Master • Shipmaster • Fleet Master • Supreme Commander|
|Special Operations||Spec-Ops • Spec-Ops Officer • Spec-Ops Commander of the Covenant|
|Honor Guard||Sangheili Honor Guardsman • Honor Guard Ultra • Light of Sanghelios|
|Specialists||Stealth • Ranger • Ascetics|
|Regular||Aristocrat • Minor • Major • Ultra|
|Civilian||Kaidon • Oracle Master|
|Heretic||Heretic Sangheili Minor • Heretic Sangheili Major • Heretic Leader|