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, and 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 being cut from the game.
 * 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.
 * The word "Strato" in the Sentinel's name is most likely derived from Latin, as "Stato" is the ablative form of "Stratus", meaning "stretched out" or "extended". It would make sense, as the Strato-Sentinel is much larger than any previously seen Sentinel variant.
 * The name of the Strato-Sentinel could also be a reference to the B-52 Stratofortress, a large United States Air Force jet, or the B-47 Stratojet, another large American plane.