ONI Alpha Site

ONI Alpha Site is one of the flashback levels in Halo 3: ODST. It is set in the ONI Alpha Base in New Mombasa.

The level is set two hours after the Squad's drop into the city, and four hours before the Rookie's awakening, from Dutch's point of view. He and Mickey are defending the ONI facility with the help of the city's Superintendent and NMPD forces.

The level opens as they are setting demolition charges to destroy the bridge leading to the complex to prevent the Covenant forces from accessing it. After the charges are armed, an NMPD officer commands the Superintendent to unlock a keypad on a bridge toll booth so they can remotely detonate the charges. The AI is hesitant at first, but eventually lets Dutch destroy the bridge. After this, they fall back deeper into the facility, fighting off more waves of Covenant until they are forced to retreat into the ONI building itself. Dutch and the NMPD officers fight off the squads of Brutes, Grunts and Jackals that continue to push into the building. Eventually the fight is brought up to the roof of the facility, where the final Covenant infiltrators are killed. A Pelican picks up Dutch and Mickey, and the level ends as Mickey remote detonates the charges in the ONI facility, destroying it.

Trivia

 * The Firefight maps Security Zone and Alpha Site are based on the level.
 * During the drop sequence when the player is in a SOEIV the ONI Alpha Site and its surroundings can be seen, including the bridge that is destroyed two hours later in this mission.
 * The trigger to start the level is a broken detonation charge from the bridge.