The facility remained in UNSC hands part way through the Battle of Mombasa. The site was defended by a New Mombasa Police Department detachment after the Prophet of Regret's departure from the city. The police officers were joined several hours later by Orbital Drop Shock Troopers Michael "Mickey" Crespo and Taylor H. "Dutch" Miles; the troopers were separated from their squad.
Officers and troopers finished preparations to demolish the access bridge as Covenant forces, including Wraiths, began to cross. The bridge's destruction forced the assault to rely on troops ferried in by Phantoms. The defenders fell back to the security zone before making a fighting withdrawal into the main structure. The destruction of the bridge and the ensuing battle led to heavy casualties on both sides.
The local NMPD commander ordered the structure destroyed to deny the enemy both ONI's data and access to the Superintendent. The structure was rigged with remote-detonated charges. A police Pelican was dispatched to evacuate remaining UNSC troops. Officers and troopers held inside the structure while they waited for the transport. They finally made their way to the roof by elevator where they were picked up for the trip to NMPD Headquarters. Once safely away, Crespo detonated the charges and demolished the building. Six hours later, when the Rookie viewed the site from the other side of the destroyed bridge, it was still burning.
During the battle, Drones attacked in the elevator and were killed. It was later revealed that there was a Drone Hive in the tunnels below the building where the Superintendent's Data Center was and destroying the building woke up the whole hive, making it much harder for Dare and Rookie to reach the data core later.
The complex is built on an artificial island inside a walled lake. The island is accessible by a single bridge. A walled security zone encompasses most of the island. The main cubic structure occupies one end of the island on the opposite to the bridge.
The main building has a large shaft in its center, which connects all the way to the Superintendent's data center deep below, ending at the top floor of the building. Each side of the shaft is occupied by an elevator. The elevators are accessible through the central platform of the building, suspended over the central shaft. The numerous offices in the building are accessible through the elevators. On the roof, there are several landing pads. On the ground floor is the ONI Memorial.
- Three Firefight maps take place in or in vicinity of the base: Security Zone is located on the hill in front of the main building, Rally Point is at the entrance to the compound in Sector 10, and Alpha Site is set in the interior of the main building.
- The doors that lead to the site is the only door that direct vehicle traffic in the city of New Mombasa that open from the ground up. All other doors that direct traffic open from the center to either side.
- When viewing the structure during Mombasa Streets, you may notice one or two Phantoms circling above it. These will continue to do so until you leave and unload the sector.
- Aside from Mombasa Streets and ONI Alpha Site, this building can also be seen in the background on the levels NMPD HQ and Coastal Highway.
- Halo 3: ODST (First appearance)