Anti-aircraft guns in the Spanish Army were considered Army Level Assets. They were neither mobile, nor were they attached to any organization smaller than a Corps.  They were used to guard airfields and other strategic targets.  At the onset of the Civil War there were just 4 batteries of 20mm and 2 batteries of 75mm AA guns in all of Spain.  The primary air defense was the anti-aircraft machine guns.*
*
Anti-aircraft guns should only be purchased in defend scenarios, and only in situations where air defense is normally a high priority.