The Defender was 5.3 meters long and armed with three laser cannons: one in the nose of the craft, and one each on either side beneath the wing. To save space and weight, the standard Defender starfighter was not equipped with a hyperdrive.
Its extendible S-foil maneuvering struts could retract into the spaceframe for non-combat situations, but once an enemy had been engaged, the struts swung down and forward to give the Defender better positioning for maneuvering-jet bursts.
While sudden maneuvers in an atmosphere actually risked tearing off the struts (due to the G-forces, the gravity of the planet itself, and atmospheric drag), in space, the Defender could literally spin around 180 degrees in mid-flight by firing one maneuvering jet forward and one backward.
The original ATL Interceptors were used by the Fromm Gang to defend Trigon One in 15 BBY.
Based upon this design, the Defender entered service with the New Republic relatively quickly in the years after the Battle of Endor. As its name suggests, it was used primarily as a short-range fighter to defend larger targets against attack.
The New Republic Defender was intended to fulfill the need for a system space and atmospheric defense starfighter. Before the Alliance to Restore the Republic defeated the Galactic Empire, its fighter design philosophy emphasized fast ships that could evade Imperial pursuit by jumping into hyperspace. However, when the New Republic gained control and the remnants of the Empire became disenfranchised, New Republic worlds became desperate for a fighter that could fend off Imperial raids.
Although the Defender was slow by contemporary standards in starfighter design (at only two-thirds of the top speed of an A-wing or TIE Interceptor), it was far faster than the aging Republic Y-wing and Z-95 Headhunters that were usually relegated to planetary defense.
The design was originally intended to deploy with the Nebula-class Star Destroyer and Defender-class assault carrier, but these ships were delayed for the best part of a decade, and although the fighter saw service in campaigns like the liberation of Kathol and at the Battle of Cadinth, it did not become as renowned as existing designs such as the X-wing or E-wing.
Eventually, some of these fighters found their way onto the black market—by 9 ABY, the smuggler Mazzic was using a pair of hyperdrive-equipped Defenders as gunships, and they impressed Talon Karrde so much, that he acquired two similarly-equipped ships of his own for use aboard Wild Karrde. Mara Jade similarly used a Defender one on her mission on Nirauan in 19 ABY. The craft she used however was not equipped with hyperdrive despite it also belonging to Karrde's organization. Jade's Defender launched from one of Karrde's ships the Starry Ice.