G.U.N.

From Sonic - Wiki on Neoseeker

G.U.N. uses a large variety of robotic forces as well as human soldiers. Most common are the "Beetle" robots; small flying machines which often have laser weapons. A few of these also have the ability to activate a personal shield. There is also a gold version which is capable of teleportation.

G.U.N.'s most famous machine is the "Big Foot". Only one was seen in Sonic Adventure 2, but two other mechs based on it were seen. The "Hot Shot" was equipped with a laser cannon. The "Flying Dog" was a legless version of the Hot Shot. All of these were controlled by a human pilot and shared a common weakness - their cockpit. Two mass-produced versions had been commissioned in Shadow the Hedgehog.