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.

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.
 * Joseph Staten stated that when the bridge blows up in Dutch's flashback, there's more to it, implying that Dutch and the marines are going to have to defend the base.