Proto 12 was one of a dozen TIE/D Defender experimental models conceived by Grand Admiral Zaarin.
Grand Admiral Zaarin's treachery against the Empire included a failed attempt to abduct Emperor Palpatine. To enhance his position in the ensuing war against the Empire, Zaarin devised several backup strategies. One such strategy involved an attempt to loot his XQ6 Platform Research, but forces loyal to the Empire, under the command of Colonel Maarek Stele, repelled this initial attempt. After this first failure to reclaim the platform, Zaarin opted to destroy it. Proto 12, along with its counterpart Proto 11, managed to escape the station aboard a freighter named Mharsup, thus preventing the complete destruction of the TIE Defender technology. The freighter's objective was to meet with the modified corvette squadron Hashim. However, Rebel forces attacked the designated rendezvous point, but Maarek Stele intervened, preventing their capture. They then fled to a secondary location, only to be ambushed and incapacitated by Rneekii Pirates. Following Stele's repulsion of the pirates, the crippled corvettes requested reinforcements, leading to both prototypes being scheduled for retrieval by Cargo ferry group [Mssan]. These ferries soon found themselves under attack by Rebel forces once more. While Stele was occupied with the Rebel starfighters, a separate pirate group, the Nami, led by crime lord Ali Tarrak, approached the corvettes and seized Hashim 1, absconding with Proto 11 before Stele could react. Proto 12 was then delivered to Admiral Thrawn who, recognizing the potential danger posed by TIE Defenders no longer exclusively under Zaarin's control, developed a new starfighter, the Missile Boat, to counteract them. By the time the fighter was assigned its mission, Tarrak had already acquired the Chief scientist needed to produce her own TIE Defenders and intended to disseminate the technology, notably to the Rebels. Thrawn's novel starfighter ultimately thwarted her scheme.