Offensive Counterair (OCA) is defined as "offensive operations to destroy, disrupt, or neutralize enemy aircraft, missiles, launch platforms, and their supporting structures and systems both before and after launch, but as close to their source as possible" (JP 1-02). OCA is the preferred method of countering air and missile threats, since it attempts to defeat the enemy closer to its source and typically enjoys the initiative. OCA comprises attack operations, sweep, escort, and suppression/destruction of enemy air defense.
OCA is the preferred method of defeating what kind of attacks? 
air and missile threats