The Redoubt was a Kig-Yar keep. It was found on the moon Metisette in the 23 Librae system, was made out of parts of old ruined ships. Built under the supervision of Reth, it housed a large river of liquid Methane that ran into an artificial crater lake. Giant reactors used to convert liquid methane into vapor surrounded the crater, creating perfect conditions for the hundreds of thousands of Unggoy who inhabited the Redoubt, to whom it also served as a breeding ground.
During the Battle of Metisette, ODSTs and two Spartans from Gray Team landed in the Plaza via SOEIV, not far from the river. They proceeded to neutralize Covenant anti-aircraft presence in the Plaza, then planted a SHIVA Nuclear Warhead in a sensor control building before being extracted by a Pelican Dropship to the UNSC Midsummer Night. The destruction of the sensor control structure blinded Covenant forces in the Redoubt, allowing it to be destroyed by several of The Rubble's asteroid habitats. Reth, the leader of the Kig-Yar forces, was killed by one of the asteroids when it collided with the ship he was attempting to escape in.