Guardian Units of the Nation Headquarters, or G.U.N. HQ for short, is the main base of operations for the Guardian Units of the Nation. It is located inside Guardian Mountain and is equipped with all the necessities needed for a military organization, including a briefing room, a recreation room, a gym, a laboratory and a hangar with helicopters and fighter jets for transportation needs.
G.U.N. HQ's laboratory was used by Hope Kintobor to build a Zone teleporter to assist Shadow the Hedgehog in the mission given to him by Commander Abraham Tower; go to the Special Zone and retieve a Chaos Emerald. Although the teleporter didn't take him to the Special Zone, Shadow managed to complete his mission anyway after going across three other zones and destroying the latest Metal Sonic. Upon his arrival, Commander Tower informed him he had a new mission; destroy Dr. Eggman's new Doom Laser, which Shadow did successfully with the help of Rouge the Bat and Sonic the Hedgehog.
Shadow and Rouge were later sent to the briefing room of G.U.N. HQ about their new mission. They were to find and recruit a rogue Eggman robot that was starting to wear down called E-102 Gamma in order to help him. Shadow requested that he not have the help of Rouge and wanted to complete this mission himself after failing to save Metal Sonic in Blaze's world. Shadow then took off in a GUN helicopter at the same time Eggman dispatched the last of the E-100 Series, E-123 Omega, to find and destroy Gamma. Although Shadow located Gamma first, Omega managed to deal with the hedgehog temporarily and destroyed Gamma, but E-102 managed to upload his free will into Omega before being destroyed, making Omega rebel against the Eggman Empire and join GUN after a talk with Shadow. After Omega was brought back to G.U.N. HQ, Shadow went off to the rec room and began talking Hope and Rouge about how he felt bad about failing to save two living weapons instead of just one. Rouge then teased him an attempt to cheer him up and Hope then gave them the folder for their next mission, using Hope's Zone-Breaching Platform to retrieve a Chaos Emerald from the Special Zone.
A moderately large room with many chairs for seating arrangements and a projector, making the room's appearance similar to that of inside a cinema. This room is used to brief agents on their next mission with pictures to help identify their targets.
The gym is an area of the base where G.U.N. agents go to either use the exercise equipment, or practice their fighting techniques in the yellow circle.
A large airfield with plenty of helicopters and fighters jets to transport GUN troops and agents to their chosen destination.
The laboratory is a high tech room used by GUN scientists and mechanics like Hope Kintobor. Hope used this room to make her Zone-Breaching Platform to assist in Shadow's mission to the Special Zone.
The rec room is an area of the base where the agents of GUN go to either relax on the sofa, get a quick drink or snack from the machines, or play a little table tennis, pocket billiards (pool) or darts with another agent.