Core Block System, The Gundam Wiki

The Core Block System is a unique mobile weapon module system designed to have any mobile weapon (traditionally mobile suits) be created or operated through the combination of multiple predesignated weapon modules guided by the pilot operating the "Core" module. Traditionally, a mobile weapon uses one of two variants of this system: A mobile weapon can be created through a series of weapon modules, which includes a Core module for the pilot (typically in the form of a stand-alone fighter plane).

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Core Block System, The Gundam Wiki

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Where do you think is the best place for a Core Fighter? : r/Gundam