Installation 03

Installation 03 is one of the Seven Halo Rings. Very little is known about it, although it is commonly confused with Insallation 05 in the level The Covenant in Halo 3. Its surface appears to be identical to that of Installation 04 (evidence that it is actually Installation 05), whereas the third ring in from Truth's location seemingly has a red, volcanic surface.

In 2552, during the Battle of Installation 05, a signal was sent to this Halo from Installation 05, putting it on standby mode. A readout from Installation 05's Control Room showed that Installation 03 was fully prepared to fire on demand.

A more comprehensive readout was later observed on the Ark, showing the inner part of the ring to be covered in what appears to be volcanic material, during the Battle of Installation 00 by the Arbiter, the Master Chief, and the High Prophet of Truth. It once again displayed that Installation 03 was on standby mode, ready to fire. However, the Master Chief deactivated the installation before it could be fired.

Trivia

 * This ring is often mistaken for Installation 05 because of the order of the rings in the level the Covenant. Although it is not so because Installation 05 is the 5th ring from the platform on which Truth and the brutes reside rather than the direction in which the player enters the area. (whereas the 5th ring in from the entrance has a volcanic surface, and this is obviously not so as Delta Halo had an identical surface to Installation 04)
 * Each holographic representation of the rings emit a sound at a certain note. These notes ascend from lowest to highest from Truth's location; further evidence that the rings are numbered 01 to 07 in that order.