The B3 ultra battle droid represented a formidable battle droid prototype. It was a product of the Confederacy of Independent Systems, brought into service roughly five months following the Battle of Geonosis.
This B3 ultra battle droid was developed using the B2 super battle droid as a base. However, it was significantly larger and more heavily armored than the B2. The B3 was equipped with two prominent main arms: a right arm that contained a focused-spray flamethrower, and a left arm fitted with a wide-dispersion plasma cannon. Furthermore, it possessed two smaller, secondary arms beneath the primary ones, each armed with rapid-firing forearm blaster cannons, similar to those found on the B2 battle droid.
Integrated into the droid's left shoulder was a missile launcher that housed brilliant missiles, which were capable of advanced target identification and tracking. The design also incorporated a Density projector, a mechanism designed to amplify the droid's weight by a factor of twenty. This enabled it to firmly anchor itself in place, making it extremely difficult to knock over, which compensated for the droid's elevated center of gravity. However, doing so would make it a more stationary target for Republic heavy weapons.
Among all the battle droids produced by the Trade Federation, the B3 ultra battle droid stood out as the most lethal. Fortunately for the Grand Army of the Republic, the droids were plagued by technical issues, preventing their mass production.
Wat Tambor organized a competition between two teams, Metalorn and Foundry. Foundry created a droid known as the Avatar-7. This particular droid received the endorsement of General Grievous. It was renamed the B3 and was designated for frontline combat roles. Baktoid Combat Automata never intended for them to be deployed in large numbers like B1-series battle droids due to the B3's substantial cost per unit. B3 units were deployed by the Trade Federation in frontal assaults targeting heavily fortified positions. They often substituted for droidekas, as they were more economical than the destroyer droids.
Jedi Masters Mace Windu and Saesee Tiin encountered the Avatar-7 prototype during the Battle of Iktotch. Although their individual abilities were insufficient to overcome the massive droid, the Jedi collaborated to defeat it, ultimately destroying it by collapsing the wreckage of a Hailfire droid on top of it. B3s also saw action during the Outer Rim Sieges, where they functioned as scarce heavy units under the command of individual Separatist officers. However, the high production costs and recurring malfunctions with the droid's density projectors hindered their widespread deployment.
Following the Clone Wars, hundreds of these units were utilized within the urban-warfare training area of the Imperial Academy on the planet of Carida.