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GAT-X255 Forbidden Blue

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GAT-X255 Forbidden Blue




Unit Type

Prototype Transformable Amphibious Mobile Suit




Model Number
  • GAT-X255
Developed from
Developed into
First Seen
Last Seen
Known Pilots

General Characteristics

  • Ultracompact Energy Battery
Pilot Accommodations
  • Pilot only, in standard cockpit in chest
  • Phonon maser cannon searchgray_iconsmall.png
  • 2 x Supercavitating torpedo canister pod searchgray_iconsmall.png
  • 4 x Built-in "Nidhoggr" heavy scythe searchgray_iconsmall.png
  • 2 x "Igelstellung" 75mm multi-barrel CIWS searchgray_iconsmall.png
  • 2 x "Armfeuer" 115mm machine gun searchgray_iconsmall.png
Special Equipments and Features
  • IR sensors searchgray_iconsmall.png
  • Sonar searchgray_iconsmall.png
  • Lorenzini sensors searchgray_iconsmall.png
  • Ultra-low-light cameras searchgray_iconsmall.png
  • Tail extension searchgray_iconsmall.png
    • Ultra-long-wave antenna searchgray_iconsmall.png
    • Towed sonar array searchgray_iconsmall.png
    • Anchor searchgray_iconsmall.png
Optional Equipment
  • Trident searchgray_iconsmall.png

The GAT-X255 Forbidden Blue is a Mobile Suit Variation from the series Gundam SEED.

Technology & Combat Characteristics

A variant of the GAT-X252 Forbidden and the first amphibious mobile suit produced by Earth Alliance, Forbidden Blue's propulsion, sensor and weapon systems have been modified to fit its amphibious role. Although the CIWS guns and arm mounted machine guns are unusable in water, they are still retained as they can be used after the MS has surfaced. The plasma cannon and railguns used by the original Forbidden are replaced by a phonon maser cannon and torpedo launchers, while the heavy scythe is quadrupled and changed into retractable weapons built into the shields. A trident now serves as the suit's handheld weapon and a tail extension containing multiple equipments is added to the backpack to improve Forbidden Blue's aquatic performance.

Forbidden Blue retains the Trans-Phase armor, "Geschmeidig Panzer" energy deflection armor and the ability to transform into a high-speed assault form. The primary purpose of the energy deflection armor is different from that of Forbidden Gundam, they are employed in Forbidden Blue as pressure hulls and to move through water. A total of 4 units were produced and the data obtained from these units were used in developing GAT-706S Deep Forbidden and later, GAT-707E Forbidden Vortex.


  • "Armfeuer" 115mm Machine Gun
Mounted on each forearm, usable only after the MS has surfaced.
  • Built-in "Nidhoggr" heavy scythe
A pair of retractable close combat heavy scythes are built into each shield, for a total of four scythes. The heavy scythe is previously a handheld weapon used by the original Forbidden.
  • "Igelstellung" 75mm Multi-Barrel CIWS
Two of these light projectile weapons are mounted in the MS's head and usable only after the MS has surfaced. Although classified as Anti-Air, they can be used for missile interception and to destroy lightly armored vehicles.
  • Phonon Maser Cannon
The Phonon Maser Cannon is a sonic weapon that is unaffected by water, allowing it to function as an effective weapon both on land and in the sea. It is mounted on the backpack but only usable in high-speed assault form. This weapon is the only energy weapon installed on the suit.
  • Supercavitating Torpedo Canister Pod
A pair of them are mounted on the backpack identical to where the Forbidden Gundam's railguns are, and fire supercavitating torpedos, a type of torpedo faster than normal ones. They are usable only in high-speed assault form.
  • Trident
An optionally handheld close combat weapon.

System Features

Like the original GAT-X252 Forbidden, the main special feature of the suit is its "Geschmeidig Panzer" energy deflection armor, which is mounted on the two shields of the suit. On the Forbidden Blue, this system is primarily used to move through water and counteract water pressure. However, it is flawed 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, thus earning it the unflattering nickname "Forbidden Coffin". This design flaw is later corrected in the GAT-706S Deep Forbidden and the GAT-707E Forbidden Vortex, with both suits featuring an additional reinforced titanium armor around the cockpit, granting the pilots survival if the Geschmeidig Panzer failed.
  • Tail extension
The Forbidden Blue is equipped with a tail extension, which mounts an ultra-long-wave antenna, a towed sonar array and an anchor. The first two equipments grant the suit advanced sensor capabilities when used underwater, while the anchor can also be used as a close combat weapon due to its sharpness.
Besides all these features the suit is also equipped with the new Trans-Phase armor, similar to the one used on the original Forbidden.
  • Sensors
Besides the one mounted on the tail extension, the Forbidden Blue is equipped with a large number of different sensor systems, granting it superior underwater sensor capabilities. These sensors include IR sensors, a sonar, lorenzini sensors and several ultra-low-light cameras.


After ZAFT forces stole four out of five of the Gundam-type mobile suits created as part of the G Project by the Earth Alliance, the EA created a new set of Gundams, this time made up of only three units. One of these suits was the Forbidden, piloted by "Biological CPU" Shani Andras. The design of the Forbidden was eventually converted into a new series of underwater-use mobile suits to counter ZAFT's underwater models. Forbidden Blue was the first of these new models as well as the prototype unit, it greatly resembled the original Forbidden and also used many system features and weapons installed on the original unit. These equipments were however partly replaced or expanded to make the suit more efficient underwater. Also the new Forbidden Blue does not utilize a Biological CPU like the original Forbidden, but instead relies on a standard Natural-use operating system.

One Forbidden Blue was tested by underwater ace Jane Houston, who used such a suit in the Second Casablanca Sea Battle on July 24, CE 71, which also marks the formal introduction of the Forbidden Blue in battle. Another unit was covertly transferred by Muruta Azrael to Orb's Rondo Sahaku faction. Data collected from the usage of Forbidden Blue were used to create the mass production units, GAT-706S Deep Forbidden and later, GAT-707E Forbidden Vortex. Both of these suits fixed a design flaw regarding the use of Geschmeidig Panzer system underwater and visually, the Forbidden Vortex is indistinguishable from the Forbidden Blue.



External Links

Forbidden Blue on MAHQ

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