From Halopedia, the Halo wiki
The Strategic Response Unit is a group of three high-level UNSC Naval Intelligence personnel. Located on the fortress world Reach, they were responsible for decision-making during major crises such as the Covenant invasion of Harvest. Following the Harvest incident the Strategic Response Unit requested that Vice Admiral Preston Cole return to active service. After the glassing of Second Base and Green Hills, they decided to inform the public of the Covenant threat and to give Cole his own fleet.