Although not shown in any of the Star Wars movie
s (4 as of this writeup), the "GUN" is used by the Imperials
It has 2 laser cannons, 2 ion cannons, shields, and hyperdrive. While it can be used as a fighter, it is best suited for taking out Y-Wings or disabling or attacking larger ships.
Although it has ion engines, this was designed and manufactured by Cygnus Spaceworks, so it isn't in the Twing Ion Engine series.