Caesar's Ghost

I have been playing CMBO for awhile, and now CMBB. My opponents (a couple of old friends who I play by email or TCP/IP) never use aircraft. Last battle against one of them, low and behold about four fighter bombers showed up. A Stuka did some pretty good damage with its bombs, taking out one entire Platoon and shocking 5 tanks, gun damaging 2 of them on one pass with just two bombs. Luckily on the second pass its bombs mostly missed. Therefore, for the next game I bought some 25mm AA guns for the Russians. On my first move I unhid my AA guns, thinking that if an enemy plane flew over that the AA guns might not fire if they were hidden. Instead, they started shooting at advancing enemy infantry, even though I heard a plane fly over. QUESTION: If I hide my AA guns, will they unhide and shoot at enemy airplanes if the enemy airplanes come into their sight? I would hate to lose my AA guns to enemy artillery and mortars before his planes even show up. What are effective AA gun tactics? Thanks for your help!