- "The raid on the Republic capital succeeded. My cortosis droids are invincible, and my factories unassailable!"
- ―Wat Tambor, following the Confederacy's attack on Coruscant
Their outer shells were made out of cortosis, a substance that could block lightsaber attacks. The black outer shell was clamped to the droids' frame in formfitting plates. The droids also had the same intelligence matrix as the similar B2 super battle droid; however, they lacked the gripping hands of the B2 battle droid, since their arms ended in double high-intensity laser cannons. The ball joint of the wrist allowed the cannons to swivel in almost any direction. The droids could also use their arms to block lightsaber blades.
There was one weakness to lightsabers in the droids' armor, discovered by Anakin Skywalker. A very precise overhead slash with a lightsaber targeting the small gap between the two breastplates would slice a cortosis droid's torso in half.
Production began when Wat Tambor put two internal teams against each other for the upcoming Separatist B3 unit. The Avatar-7 was selected over the cortosis battle droids, so the cortosis droids were manufactured as the C-B3.
C-B3 droids were first deployed in limited numbers on Tatooine, but were used more extensively in the attack on Coruscant and the defense of the Techno Union foundries on Metalorn. Their deployment showed that they were extremely effective—too effective, in the eyes of Darth Sidious. Believing that they could tip the balance of the war, Darth Sidious, secretly Supreme Chancellor Palpatine, allowed information about the droids' location on Metalorn to reach the Jedi Order.
- Star Wars: The New Droid Army (First appearance)
- The New Essential Guide to Droids
- The New Essential Chronology
- The Clone Wars Campaign Guide
- The Complete Star Wars Encyclopedia
- The Essential Guide to Warfare