From Halopedia, the Halo wiki
Following the Banished's ambush on the UNSC Infinity upon its arrival at Installation 07 on December 12, 2559, UNSC forces made landfall on the ring. While many survivors at the fragmented section of the ring gathered at the wreckage of the Mulsanne-class frigate UNSC Mortal Reverie as a base of operations, they also established Forward Operating Bases in nearby locations. FOB Delta was located east of the Conservatory, and northeast of a Reformation Spire's base.
By March 3, 2560, FOB Delta was in Banished control, with the Banished adding their own equipment and troops around the FOB. The FOB was also connected to the Banished battle network protocol, tracking nearby UNSC and Banished activity. At some point after Master Chief Petty Officer John-117 was retrieved by Fernando Esparza onboard Echo 216 on May 28, the Spartan eliminated the Banished forces at the FOB and deployed his artificial intelligence known as the Weapon at the FOB's terminal. The Weapon removed the FOB from the Banished network, returning it to UNSC control, and marked the nearby locations of interest on John-117's TACMAP.
FOB Delta becomes available in the "Connections" section of the Halo Infinite campaign.
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