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Fireteam Castle was a team of five Spartan-IVs of the Office of Naval Intelligence. Castle was assigned to UNSC Infinity at some point before early 2557 and fought on the Forerunner planet Requiem. All members were killed while delivering supplies to Copernicus Base.
- On July 21, 2557, Castle was deployed alongside Fireteam Shadow to the surface of Requiem to suppress Jul 'Mdama's Covenant attacks on Gypsy Company.
- On February 8, 2558, Castle was defeated by Fireteam Majestic in a War Games match.
- Fireteam Castle's emblem appears in Halo 5: Guardians as an ultra rare REQ.