How many zaps do I need for air defense?

How many zaps do I need for air defense? It takes no less than 3 Lightning Spells to take out an Air Defense of any level, and higher level air defenses require higher level Lightning Spells to take them down.

It takes no less than 3 Lightning Spells to take out an Air Defense of any level, and higher level air defenses require higher level Lightning Spells to take them down.
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