The Jammer job first appeared as a job that was used by enemies in Front Mission 4 before appearing in Front Mission 5: Scars of the War as a job that is used by both enemies and player units.
Front Mission 4[]
In Front Mission 4, enemy Jammer units are notable for using melee weapons and for being the only enemy units to use EMP backpacks; these can inflict a variety of status effects on player units, such as disabling their ability to attack or move.
Front Mission 5[]
In Front Mission 5, the Jammer job is usable by players as well as enemies. Player Jammers can learn skills that allow them weaken enemy units in addition to skills that let pilots take less damage or avoid it entirely.