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This article is about campaign level. For Halo 3 achievement, see Cleansing (achievement).


Shield World



HW-11 Cleansing.jpg


Halo Wars


James Cutter


February 2531


Spirit of Fire, upper deck, inside a passage that leads into the interior of the Etran Harborage.


  • Permanently Remove the Flood Structures
  • Clean the Flood off the Hull
  • At Least One Airlock Must Survive
  • Garrison Squads into the Airlocks to Protect Them


  • Kill 100 Sentinels
Halopedia has a walkthrough guide to this level, Cleansing. See Cleansing/Walkthrough.
Cleanse the infection forms from Spirit's hull before they penetrate the interior.

Cleansing is the eleventh campaign level of Halo Wars. This is the first and only level the player can control Cyclops, and second level to control the Gremlin.

After the UNSC Spirit of Fire is pulled beneath the surface of an unknown planet, it is revealed that there are Flood on the ship and Sergeant John Forge is tasked with cleaning them off. Very soon, Sentinels appear to clean off the Flood, and deem the UNSC a threat. The Spirit of Fire's AI Serina intercepts an alien signal noting that they needed to eliminate the Flood off the ship, and a "Cleansing Ring" is needed for this. Sergeant Forge, along with Marine squads, Red Team Spartan IIs, Wolverines, Hornets and Turrets, kill and destroy all the Flood hijackers.

After that, they proceed to disable all other Flood forms that are stuck onto the ship, but only a Cleansing Ring will permanently kill the Flood. Super Sentinels soon arrive to clean off the Flood. When the cleansing ring approaches, Serina orders all ground units including the Sergeant into airlocks, while she advises the Hornets to head the opposite way the cleansing ring is approaching so that damage to the air vehicles is minimized. They eventually succeed to clear every Flood form on top and Captain Cutter orders the ship to get out of the tunnel they are in.


The UNSC Spirit of Fire enters the entrance portal to interior Dyson sphere of the Etran Harborage, surrounded by Aggressor Sentinels. Soon into the journey, the Flood are detected on the ship's outer hull.

In order to pass through the docking rings, Sergeant John Forge and the Spirit of Fire's crew work to cleanse the ship's hull of the Flood while avoiding the Sentinels and cleansing ring sent by the installation's AI. After a struggle, the Spirit of Fire's forces manage to clear the hull and the ship makes it through the entrance portal.



The UNSC Spirit of Fire is seen going through the split in the ocean. The Spirit activates its headlights as the split behind it closes. Aggressor Sentinels continue to fly around the Spirit. One flies in front of the bridge and observes Captain Cutter before flying off.

  • Serina: "This is all part of the plan... right, guys?"

The ship continues to fly through what appears to be a massive underground Forerunner structure.

{In-Game Cutscene}

  • Captain James Gregory Cutter: "Serina, report! What's going on here?"

Two Sentinels fly towards where the Spartans, Forge, and some Marines fight off Flood. Flood dispersal pods start dropping everywhere, one of them hits one of the Sentinels. The UNSC forces eliminate a few approaching infection forms.

  • Serina: "Best guess, we're being pulled through some sort of docking system. That alien life form followed us in, we have a significant infestation on the aft quarter."
  • Cutter: "Forge, get out there and get those things off my ship!"


  • Cutter: "You can requisition troops from the airlocks on the deck, if we lose those airlocks, we'll be defenseless."

More Sentinels fly in, as well as a couple of Protectors being lead in groups by Sentinels. More Flood dispersal pods drop and land on the hull.

  • Serina: "Those aliens are dropping pods on the hull from all around us, keep watch for them."

The UNSC forces continue to eliminate Flood forms.

  • Serina: "Alien population on the hull is increasing, and the structure is reacting, more of those drones inbound too."

In addition of the Flood, the UNSC forces also destroyed the Sentinels.

  • Serina: "Bad news, I intercepted a signal from the alien AI. Those drones have declared us a threat and are massing behind us."
  • Forerunner AI: "Decontamination sequence commencing."
  • Serina: "Sergeant Forge, get your men into the airlocks. Something very bad is coming."

{In-Game Cutscene}

A formation of Hornets fly over the aft hull as more Flood dispersal pod drop on to the hull. The Spirit of Fire is going through a ring-shaped energy field, which is clearing away the Flood from her hull.

  • Serina: "The energy field is reacting to the aliens, it's trying to clean our hull, take cover out there!"


  • Serina: "Captain, if our air units fly through the ring in the opposite direction it will minimize damage."

Flood structures that were regenerated are removed by the energy field.

  • Serina: "The drones and the cleansing ring seem to be able to remove the aliens if they're already damaged."

A timer appears: 02:00. Once the countdown reaches zero, the Forerunner AI will make an announcement, and the Spirit of Fire flies through the next cleansing energy field. This will continue until all the Flood is cleared off the ship.

When enough Sentinels are killed, Super Sentinels will show up to help the Aggressor Sentinels and Protector Sentinels.

Once the countdown to the second ring reaches zero:

  • Forerunner AI: "Decontamination sequence commencing."
  • Sergeant John Forge (COM): "Take cover! Another cleansing wave is coming."

Once the countdown to the third ring reaches zero:

  • Forerunner AI: "Decontamination sequence commencing."
  • Forge (COM): "The ring is back!"
  • Cutter: "Two Vultures have just finished repairs, they're yours to command."

Once the countdown to the fourth ring reaches zero:

  • Forerunner AI: "Decontamination sequence commencing."
  • Serina: "Take cover!"

The UNSC forces destroy all of the Flood structures and forms.

  • Forge (COM): "All clear! The hull is clean."
  • Cutter: "Serina, maximum power to the engines. Get us out of here!"

Level ends.


  • Near the start, Sentinels are shown as yellow blips on the mini-map, but after the first ring comes, they are shown as red blips.
  • On closer inspection, one will notice that the whole level is an optical illusion, as the Spirit of Fire is not actually moving, the walls are. This can be seen properly if one moves the camera up against the tunnel walls and looks at the Spirit.
  • This level introduces what is, functionally, a miniature Halo Array, except that rather than having an effect range on a stellar scale, the ring only creates an energy field within its own diameter, destroying any form of life, including Flood. However, because the energy field also causes damage to inorganic matter, such as vehicles and buildings, and does not cause instantaneous death, the technologies used to create the two systems are shown to be unrelated. While entering the insides of the planet, the crew aboard the UNSC Spirit of Fire must travel through a narrow tunnel through the thin crust of the Shield World's outer sphere. The miniature Halo Array "cleanses" any Flood or unknown sentient species, protecting the interior of the Etran Harborage. Nonetheless, the Flood have apparently found a way to bypass this quarantine system, and have successfully taken hold on the Shield World's interior, as is revealed in two levels later, Beachhead.


Preceded by
Shield World
Halo Wars campaign missions
Succeeded by