The Delta Halo is a ring that the Forerunners built as a device to eradicate the Flood by depriving them of flood. Essentially, the Delta Halo, like all the other rings, would send out a pulse that would eradicate all life within 25,000 light years of it. This ring could only be activated by someone human. It was first shown in the Halo series in Halo 2. In Halo 2, a brute cheiftan called Tatarus tried to activate the ring with the unwitting help of a UNSC member called Miranada Keyes, but was stopped thanks to a member of the Elites called the Aribiter and another member of the UNSC forces, Sgt. Johnson.