The Gigan is a fortress defense MS, and is practically a moving battery. The lower body does not have feet for walking, the Gigan's movement is instead done with three wheels and four auxiliary thrusters. The cockpit is a double-seat type to accommodate the pilot and a gunner. The lower half of the body is replaced with a high mobility vernier for space, allowing it to operate as a space warfare MS, similar to the MSN-02 Zeong. Its main and most prominent weapon was the 180mm recoilless cannon mounted on the top of the Gigan's head, which served as the weapon of choice for long-range bombardment. For use in close to mid-range combat the Gigan also featured a 120mm four-barrel machine gun mounted in the place of its right forearm.
In the year U.C. 0096, the Gigan units deployed by the Sleeves had their front two wheels replaced with the same large propellant boosters used by the YAMS-130 Krake Zulu, and the rear wheel has been abolished. The 120mm four-barrel machine gun was also replaced with the same Gatling Gun utilized by their customized MS-21C Dra-C.