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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]

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]



The complex that would later become CASTLE base was originally a titanium mine, but was closed down in the 2520s or 2530s[Note 2] after the mine breached the Forerunner complex below. The mine would be used for storage for several years before being put into action by the Office of Naval Intelligence.[7]

Fall of Reach[edit]

Main articles: Fall of Reach, Raid on Reach

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 Frederic-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.

Return to CASTLE base[edit]

Main article: Operation: WOLFE

In October 2559, Blue Team once again returned to CASTLE base seven years following the base's destruction. Following the emergence of the Created led by Cortana and the subsequent conflict, Blue Team were ordered to breach the rubble of CASTLE and recover assets from Halsey's abandoned laboratory, believed to be key to defeating Cortana's forces. Despite the destruction of the base itself, the lab survived, guarded by a subroutine that Kalmiya had left behind to protect the cryo-vault. With some difficulty, Blue Team succeeded in extracting the assets back to the UNSC Infinity.[8] Using what Blue Team had recovered, her surviving cloned brains from the creation of Cortana, Halsey was able to create the Weapon, a copy of Cortana capable of locking her down for deletion.[9]

Known sections[edit]

  • Level Aqua
    • Section Lambda
      • Armory
  • Level Scarlet
    • Omega Wing
      • Dr. Halsey's office[10]
    • Medical wing
      • Cold storage facilities
      • Surgical bays
  • Level Lavender
    • Section Sigma

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.
  2. ^ Halo: First Strike describes the mine as having shut down two decades before the Fall of Reach, placing it in the 2520s-2530s.


  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: First Strike, Chapter 11
  8. ^ Halo: Shadows of Reach
  9. ^ Halo Infinite
  10. ^ 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.")
  11. ^ Halo: First Strike, page 134 ("Down the elevator shaft in Section Sigma,")