The SD-6 infantry droid, nicknamed "Hulk," served as a precursor model to the SD-9 and SD-10 battle droid models from Balmorran Arms. It saw action during the waning years of the Old Republic and the initial period of the Galactic Empire.
The SD-6 was a battle droid of the fourth degree, manufactured by Balmorran Arms. Towering at 3.5 meters tall and nearly as wide, it presented a formidable defensive presence, like a mechanical mountain. This droid's weaponry included two E-Web repeating blasters mounted on each arm, along with two Merr-Sonn ion gun rifles positioned on rotating shoulder mounts. Furthermore, it possessed two large arms designed for defending against melee attacks.
Similar to the earlier SD-4 and SD-5 models, the SD-6 series incorporated data illicitly obtained from the Empire's Dark Trooper Project, but it lacked a heuristic processor. This resulted in a tendency for single-minded action, hindering independent thought. The SD-6 featured an integrated comlink and either a blue or red photoreceptor that enabled telescopic vision. The droid was also protected by duranium armor, which, in certain areas, was as thick as a starship's hull, rendering it almost impervious to most personal weapon fire.
The SD-6 operated as a mobile, intelligent turret, tasked with safeguarding locations or providing suppressive fire. Its arsenal allowed the "Hulk" to unleash a heavy barrage, capable of repelling assaults from both droid and organic infantry. It proved most effective against smaller vehicles and large infantry formations. However, the droid's slow speed made it susceptible to smaller teams and mobile infantry units, who could evade its firing arcs. The SD-6 also functioned effectively alongside regular infantry units in both offensive and defensive roles, and as a battle droid commander.
The "Hulk" was created during the final centuries of the Galactic Republic and was predominantly used by the Old Republic to defend vulnerable hangar bays and landing platforms. These units provided covering fire for arriving starships and prevented enemy vessels from launching. During the Clone Wars, the Republic initially sidelined the droids to avoid confusion with the droid forces of the Confederacy of Independent Systems (CIS). However, service and production were later resumed, with Balmorra producing SD-6s for sale to Republic ground forces alongside B1s destined for the CIS.
During the reign of the Galactic Empire, the SD-6's original functions were gradually taken over by smaller and more agile droids, but the Imperial military continued to employ the SD-6. As the series was gradually retired, many units were either destroyed or sold off. Despite being illegal, some crime lords acquired these war droids to safeguard their personal starships or serve as security forces, either independently or with other subordinates. Mercenaries also obtained several SD-6 war droids. For example, Trandoshan mercenaries deployed one during their attempt to seize control of the repulsortrain Gem of Alderaan with the goal of capturing Senator Bail Prestor Organa.
Although the New Republic also utilized the SD-6, it was a rare sight during that era, as the SD-9 and SD-10 battle droids had been designed to supersede it. The few remaining units that had escaped destruction were abandoned and left to their fate.