Strato-Sentinels are a sub-order of Sentinels in the Halo universe. Considerably larger than other Sentinels, these machines are responsible for conducting heavy construction operations, carrying out duties such as gathering materials, heavy mining and even terraforming. They were notably used to help in the construction of the Halo rings. Strato-Sentinels may be employed in military roles and outfitted with naval weapons and defenses. In these contexts, they may be considered a form of weapon-ship.
Strato-Sentinels were also used by the Forerunners as escorts to keyships and larger Sentinel variants. In times of crisis, some of them would assist in combat duties.
Dark gray in colour, Strato-Sentinels are massive and powerful Sentinels that are slightly smaller than the average human frigate, which are about 478 meters in length. The upper section of a Retriever is vast and wide, while the lower section is lined with numerous mechanical, tentacle-like "legs" that move in pursuit of objects. Glowing eye-like lights are installed on the front of each Sentinel.