Retriever Sentinel

The Strato-Sentinel was a Forerunner Sentinel variant. They were designed to strip mine the resource moon located in the middle of Installation 00, to help in the the construction of the replacement Installation 04. They were also used in the construction of the Portal on Earth, in the present-day country of Kenya.

Trivia

 * Strato-Sentinels were originally planned to appear in Halo 3, but wound up on the cutting room floor.
 * One of the concepts for the remake of Lockout had the map set in the partially destroyed insides of a Strato-Sentinel orbiting the Ark's resource moon.