Suppression of Enemy Air Defence means just that: removing the enemy ability to damage your air units. Not to be confused with Air Superiority, SEAD focuses on destruction of land-based, fixed or mobile air defenses. SEAD is preparation for a follow-up air strike that takes out a primary target, such as an ACU or a Strategic Missile Launcher. This is easily one of the most difficult, yet rewarding, actions to accomplish in Supreme Commander, as it requires a good knowledge of your own units, enemy units and structures, and careful timing.