GAT-X252 Forbidden Gundam

In mid CE 71, the Earth Alliance collaborates with Muruta Azrael's Azrael Conglomerate to build three second-generation mobile suits to counter the G-units stolen by ZAFT. These designs feature a new variation of Phase Shift armor known as "Trans-Phase". Unlike normal Phase Shift, which draws power constantly, Trans-Phase armor activates only when the mobile suit is hit, and only at the point of impact, reducing the armor's power consumption and increasing combat endurance. In addition, these three suits' pilots are designated as "Biological CPUs" (noting that the the Alliance considers them equipment rather than human beings), with their abilities enhanced by drugs to match those of Coordinators.

One of these was the GAT-X252 Forbidden, a close combat mobile suit, whose "Biological CPU" was Shani Andras. Its armament includes of a pair of head-mounted CIWS guns and arm-mounted machineguns, and a handheld "Nidhoggr" scythe. However, its main weapons are mounted on its backpack, which folds over its head for "close combat mode". These weapons are a pair of "Eckzahn" railguns and a powerful "Hresvelgr" plasma cannon. In addition, close combat mode utilizes the Mirage Colloid-derived "Geschmeidig Panzer" system, which consists of two large shield pods that can deflect beam attacks.

The Forbidden is first used in the conquest of neutral Orb, then sent to space and assigned to the Archangel-class assault ship Dominion under the supervision of Muruta Azrael, who is also the leader of the anti-Coordinator terrorist group Blue Cosmos. Near the end of the war, it is destroyed by Yzak Joule in the GAT-X102 Duel.

In addition, an amphibious variant of the Forbidden was created, the GAT-X255 Forbidden Blue. It utilizes a Natural-use OS rather than "Biological CPUs", and has weapons optimized for underwater use, including a torpedo pods and a phonon maser energy cannon for close combat mode. The "Geschmeidig Panzer" system is modified so that it also provides underwater propulsion and counteracts water pressure, and also mounts two "sharp point" claws on each of its two pods. One Forbidden Blue is tested by underwater ace Jane Houston, and another is covertly transferred by Murata Azrael to Orb's Rondo Sahaku faction. Four more are stationed at Heaven's Base, the new Alliance military headquarters, in Iceland. However, the Forbidden Blue proves to be a flawed design, as it is reliant on its "Geschmeidig Panzer" system to protect against water pressure. This means that if the battery fails in deep water, the Forbidden Blue will be rapidly crushed, earning it the unflattering nickname "Forbidden Coffin". This problem is rectified in the mass-production version, the GAT-706S Deep Forbidden, with the introduction of a pressure hull. The Deep Forbidden is later succeeded by the GAT-707E Forbidden Vortex, which is largely identical to the Forbidden Blue and visually indistinguishable, but is improved internally by the inclusion of a pressure hull like that of the Deep Forbidden. At least four Forbidden Vortexes were deployed in the defense of Heaven's Base.

GAT-X252 Forbidden
Manufacturer: Earth Alliance/Azrael Conglomerate Users: Earth Alliance Unit type: prototype close combat mobile suit Head height: 17.47 meters Base weight: 85.33 metric tons Special equipment: Trans-Phase armor, "Geschmeidig Panzer" energy deflection armor Powerplant: Ultracompact energy battery Armament:  "Igelstellung" 75mm multi-barrel CIWS x2, "Armfeuer'" 115mm machinegun x2, "Eckzahn" 88mm railgun x2, "Hresvelgr" plasma induction cannon x1, "Nidhoggr" heavy scythe x1 Pilot(s): Shani Andras

GAT-X255 Forbidden Blue
Manufacturer: Earth Alliance Users: Earth Alliance, Orb Union Unit type: prototype amphibious mobile suit Head height: 17.47 meters Base weight: unknown Special equipment: Trans-Phase armor, "Geschmeidig Panzer" energy deflection armor, IR sensors, sonar, Lorenzini sensors, ultra-low-light cameras, Trans-Phase (TP) armor, tail extension (mounts ultra-long-wave antenna; towed sonar array; anchor) Powerplant: Ultracompact energy battery Armament:  "Igelstellung" 75mm multi-barrel CIWS x2, "Armfeuer" 115mm machinegun x2, phonon maser high energy cannon x1, supercavitating torpedo cansiter pod x2, sharp point x4, trident x1 Pilot(s): Jane Houston, Six Socius

GAT-706S Deep Forbidden
Manufacturer: Earth Alliance Users: Earth Alliance Unit type: mass production amphibious mobile suit Head height: 17.2 meters Base weight: 80.4 metric tons Armor: reinforced titanium (around cockpit) Special equipment: "Geschmeidig Panzer" energy deflection armor, tail extension (ultra-long-wave antenna, towed sonar array) Powerplant: Ultracompact energy battery Armament:  phonon maser high energy cannon x1, supercavitating torpedo cansiter pod x2, sharp point x4, trident x1 Pilot: Jane Houston

GAT-707E Forbidden Vortex
Manufacturer: Earth Alliance Users: Earth Alliance Unit type: mass production amphibious mobile suit Head height: 17.47 meters Base weight: 85.2 metric tons Special equipment: Trans-Phase armor, "Geschmeidig Panzer" energy deflection armor, IR sensors, sonar, Lorenzini sensors, ultra-low-light cameras, Trans-Phase (TP) armor, tail extension (mounts ultra-long-wave antenna; towed sonar array; anchor) Powerplant: Ultracompact energy battery Armament:  "Igelstellung" 75mm multi-barrel CIWS x2, "Armfeuer" 115mm machinegun x2, phonon maser high energy cannon x1, supercavitating torpedo cansiter pod x2, sharp point x4, trident x1