Lightning Gun: FAIL. From Popular Science:
We at PopSci appreciate new weapons. And lasers. And laser weapons. Which is why we're excited to tell you that the Navy and the Marines have given a company called Applied Electronics about a million dollars to attach lasers onto planes. The weapons would be ultra-short-pulse (USP) lasers, which shoot beams of frequent-pulse light that create a path through the air, via which bolts of electricity can travel toward a target.
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Update: Lightning Gunners Take to the Skies -- The Danger Room