Halo Alpha
Halo Alpha

A Retriever[1] also known as a Strato-Sentinel was a Forerunner Sentinel variant. Retrievers were designed to strip mine the resource moon located in the middle of Installation 00 using an artificial gravity beam to remove the materials from its surface[2][3] which are used to construct and repair various Forerunner installations.[4]


In 2555, after the Portal was reopened to reach the Ark, a lone retriever crossed it, and began harvesting Earth's minerals before being destroyed by a UNSC warship.[5] Five more attacked the Mayhem on the Ark, after he crossed the portal, but all were destroyed by the ex-Covenant's ship, which was downed.[6] Later, 000 Tragic Solitude launched a massive Retriever's force to attack Earth. Most were destroyed, but also caused heavy UNSC casualties. Earth's destruction only stopped after the Solitude, under attack of the Mayhem's crew, recalled them. The Monitor's destruction left all Retrievers intact but floating adrift in the space.[7]


  • Retrievers were originally planned to appear in Halo 3, but were cut from the game.
  • The word "strato" in the Sentinel's name is the Latin ablative form of "stratus," which means "stretched out" or "extended."[8]
  • One of the concepts for the Halo 3 multiplayer level Blackout had the map set in the partially-destroyed insides of a Retriever orbiting the Ark's strip mining moon.




  1. Halo Waypoint - Halo 101 - Sentinel Factory
  2. Halo: Hunters in the Dark, page 119
  3. The Art of Halo 3
  4. Halo 3: The Cradle of Life, page 2
  5. Halo: Hunters of the Dark - p.123
  6. Halo: Hunters of the Dark - p.142-152
  7. Halo: Hunters of the Dark - p.355
  8. Wikitionary's definition of stratus