A flak gun is a point-defense weapon designed and put into service sometime during the Reconstruction period. Oddly enough, the Shivans also seem to have adopted this technology at some point prior to their reappearance in the Second Shivan Incursion.
Flak guns fire highly visible projectiles that explode violently near targets, damaging anything within their blast radius. While flak projectiles do negligible damage against shielded targets, their effective blast radius, coupled with the guns' high rate of fire, makes flak guns a considerable threat against unshielded or partially shielded targets; prolonged exposure to flak fire can also wear down even the most heavily shielded fighters and bombers.
While flak guns are moderately effective against most unshielded vessels and poorly shielded strikecraft due to their superior accuracy and high rate of fire versus the so-called "blob turrets", they do almost no damage against subsystems and are nearly useless at intercepting bombs as the projectiles often explode harmlessly a good distance away instead of directly hitting the intended targets.