The Marine Corps MOS 6400 is for Basic Avionics Marine IMA. This MOS provides direct and indirect support for all aviation weapon systems. Marines with this MOS work within a Marine Aviation Logistics Squadron (MALS). They support squadrons under the command of their parent air group. They rarely interact with aircraft directly, but they specialize in a specific group of electrical.
Marines with MOS 6400 progress through specific hard skill MOSs and ultimately are assigned MOS 6391, Avionics Maintenance Chief. The Avionics Chief (MGySgt) serves as the OccFld sponsor for all 63/6400 MOS within the MAG.