Forerunner secondary reactor

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An inactive Forerunner secondary reactor on Harvest.

The Forerunner secondary reactors, sometimes referred to as bonus reactors, are Forerunner generators. They are characterised by their circular structures with four pylons pointing upwards to its "chimney". Each reactor features a walkway outlining the building's edge. The hollowed center emits a bright blue light when the reactor is in use. These reactors have been found on Harvest, Arcadia, on the surface of the shield world Etran Harborage, and within its interior.[1]


The Forerunner secondary reactors are reactors built and used by the Forerunners in their ground based attacks. In some battles, they had time to retreat and detonate them. On occasion they were overwhelmed by the Flood and were not able to destroy them.[2]

By 2531, when UNSC forces from UNSC Spirit of Fire explored the surface of Etran Harborage, at least two of these reactors remained intact and operational despite the Flood's domination over the shield world's surface. UNSC forces were able to reactivate these reactors, which provided similar level of power generation as their UNSC counterparts.[3]

An active secondary reactor on the Flood-infested surface of Etran Harborage.


The Forerunner secondary reactor is a building found in Halo Wars campaign and multiplayer. It increases the tech level of any player that stations an infantry unit within it, allowing players to bypass the need to construct the UNSC reactors or Covenant temple.

Two secondary reactors could be found in the campaign level Shield World. The building is much more common in Skirmish maps, typically defended by rebels, the Flood, or Aggressor Sentinels. Units garrisoned in the structure receive the same defensive bonus as they would in a deployable lookout tower. Although the building itself cannot be destroyed, the infantry inside can be killed, allowing the structure and its benefit to be contested between players.

List of appearances[edit]


  1. ^ Halo Wars
  2. ^ Halo Wars: Official Strategy Guide
  3. ^ Halo Wars, campaign level Shield World