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The location of CASTLE Base on Reach (identified here as "CAS").

CASTLE Base was an Office of Naval Intelligence underground facility located within the FLEETCOM Military Complex[1] in Csongrád[2] on the human colony of Reach. It was hidden two kilometers directly underneath Menachite Mountain, part of the Highland Mountains in the Viery Territory.[note 1] Protected by massive amounts of granite, reinforced concrete, plates of Titanium-A armor, and EMP-hardened metal,[3] it was virtually bombproof, well defended, and nigh-impenetrable.[4] The complex was originally a titanium mine, but was closed down after the mine breached the Forerunner complex below.

Dr. Catherine Halsey had an office in CASTLE Base's Omega Wing, as did Colonel James Ackerson. The SPARTAN-IIs were familiar with CASTLE Base, some of their training having taken place in the base[5] as well as the abandoned mine tunnels around it.[6] During the Fall of Reach, the base was Team Delta's fallback position. William-043, Vinh-030, and Isaac-039 arrived there. They were soon joined by Fred-104 and Kelly-087. There, they discovered Dr. Halsey, who had remained behind to initiate Operation: WHITE GLOVE, destroying the base to prevent the Covenant from acquiring advanced UNSC technologies.

When the Covenant forces breached the base, Dr. Halsey was forced to put Operation: WHITE GLOVE into action, destroying the base and deleting her AI assistant Kalmiya. This prevented the Covenant from gaining any intelligence from the base. Halsey and the Spartans then retreated into the dangerous titanium mines below, and later to the Forerunner complex, where they discovered a powerful Forerunner crystal.

Known sections[edit]

  • Level Aqua
    • Section Lambda
      • Armory
  • Level Scarlet
    • Omega Wing
      • Dr. Halsey's office[7]
    • Medical wing
      • Cold storage facilities
      • Surgical bays
  • Level Lavender
    • Section Sigma
      • Elevator shaft[8]

List of appearances[edit]


  1. ^ The planetary map of Reach that comes with the Halo: Reach Limited Edition has "CAS" marked in the central mountain range of the Viery Territory. Judging by how SWORD Base's location is marked a similar callout "SWO" and Visegrad as "VIS", this places CASTLE Base in the Viery Territory.


  1. ^ Halo: The Fall of Reach, page 229 (Chapter 25 heading)
  3. ^ Halo: First Strike, page 100, ("Although he barely felt the descent, Wagner knew he had dropped three kilometers into the planet, through solid layers of granite, reinforced concrete, plates of Titanium-A, and EMP-hardened metal. None of this made him feel any safer, though; ONI's research facility on Reach had the same setup, and it had not done those poor bastards any good.")
  4. ^ Halo: The Fall of Reach, page 229 ("CASTLE was a massive complex, two thousand meters below the granite protection of the Highland Mountains — bombproof, well defended, and impenetrable.")
  5. ^ Halo: First Strike, page 132
  6. ^ Halo: The Fall of Reach, Chapter 8
  7. ^ Halo: The Fall of Reach, page 229 ("The private office was located deep underground, inside the "Omega Wing" of the super-secure ONI facility, code-named simply CASTLE.")
  8. ^ Halo: First Strike, page 134 ("Down the elevator shaft in Section Sigma,")