Offensive Counter Air - An offensive counter air (OCA) mission is an offensive air activity conducted to destroy, degrade, neutralise or disrupt adversary air power, or to contain it as close to its source as possible. OCA missions can involve fighter sweep and the suppression of enemy air defences (SEAD). Destroying adversary air power and air defence threats on the ground is traditionally regarded as the most effective way to conduct OCA missions.
Defensive Counter Air - A defensive counter air (DCA) mission utilises active or passive defensive measures to detect, identify, intercept, destroy or neutralise the effectiveness of adversary air activity and to prevent the adversary from achieving control of the air. These missions are normally conducted over or close to friendly territory, and aim to avoid or minimise the damage to friendly forces whilst inflicting the maximum attrition on the adversary.