Installation 04 is a Halo: Reach Firefight map from Halo: Combat Evolved Anniversary and the Anniversary map pack. It set at one of the towers from the Halo: Combat Evolved/Anniversary campaign level Halo. At the beginning of each game, there are four ODSTs who stay around the area of the main structure in the center. They slowly descend to ground level as the waves progress. In addition to weapon drops at the end of each round, every five waves a Pelican may drop a Warthog with ODSTs to aid the SPARTAN players and make things difficult for the Elite players.
- This is the first Firefight map to have Human AI allies.
- The first four ODSTs stick to the middle structure and never stray too far from it. ODSTs dropped from a Pelican will follow the players.
- Right before every bonus round, all AI allies die.
- Only ODSTs dropped off via Pelican can enter vehicles (Warthog, Mongoose). The four ODSTs that spawn in the beginning on the structure will not ride with the player.
- The map hosts an easter egg in the far building from the first spawn where a Monitor will appear behind the glass door at the beginning of a game. When approached, if playing as a Spartan, the text "Change weapon with ally" will pop up showing a Focus Rifle, but no swap can be made.
- There is a Spartan toy on this level, just like the other 6 maps from the Anniversary map pack.
- This is the only level where the player can kill human AI as an Elite.