The Radar Jammer Edit
Radar jammers are devices mounted on certain units that allow it to jam the enemy's radar unless they have line-of-sight of the source of the jamming or Omni-Sensor-Radar. Jamming is when several radar signatures appear in places where there are no units thus confusing defenses about the real unit to shoot at until it's actually seen.
Using Jamming Edit
Jamming is useful for covering invasion forces and such because since a single jammer makes several signatures it is hard to determine which way an attack is coming from.