Mechs, unlike vehicles, are combat-specific machines rather than simply for transportation. They're almost always humanoid (having legs and/or arms), and most of the time only have enough room for the pilot. Some mechs are mass produced and known under one general name, but every now and again GUN engineers a super mech for high-intensity battle.
Super Mechs
B-3X Hotshot
The first super mech ever created (or at least used) by GUN, the Hotshot was destroyed by Shadow the Hedgehog in its attempt to subdue him at the beginning of the events of SA2. Like its successor, F-6T Bigfoot, Hotshot's features include a gattling gun below the cockpit, missiles mounted at either shoulder, and hover thrusters below the engine.
F-6T Bigfoot
GUN's second super mech is almost identical to its predecessor, the B-3X Hotshot. The Bigfoot was used against Sonic after his escape from GUN custody when he was mistaken for Shadow the Hedgehog. It carries one pilot, and features a gattling gun by the cockpit, missiles mounted on either shoulder, and hovering boosters behind the engine.
Bigfoot's design was later downgraded into one of the mass-produced mech styles.
R-1A Flying Dog
GUN's final attempt at a super mech during the events of SA2. Like F-6T Bigfoot and B-3X Hotshot before it, Flying Dog features the same gattling gun, missiles, and hover thrusters as usual, but unlike its cousins, Flying Dog is aerial-only. Maybe GUN thought this would make it harder to attack or something. It was still destroyed by Rouge the Bat in the end anyway.
Heavy Dog
To be written.
Blue Falcon
To be written.
Diablon.
To be written.