In essence a much larger version of the Colicoids' droideka, the annihilator droid was armed with two dual rapid-fire laser cannons cocked back in the menacing form of a rampant scorpion. It could target with either a crimson photoreceptor, or with a composite radiation sensor. It also carried a combination particle-energy shield, similar to the shield produced by the annihilator's smaller cousin. Because of this extra shield, droidekas would position themselves inside the annihilator's shield for more protection. With fewer than one hundred annihilators on Colla IV, the Colicoids placed them around strategic or political resources.
In the later stages of the Clone Wars, Republic forces launched an attack on Colla IV, where a single annihilator droid took out three of the four platoons of clone troopers that had been advancing on the shielded factory. Advanced Recon Commando Stec was one of the survivors. Knowing more Republic forces would arrive, a CIS task force was arranged by the Colicoids to ship the annihilators to the front lines of the war. Annihiliator droids also participated at the Battle of Formos and the Battle of Palanhi, where they scored victories for the Confederacy.
With the rumor that a single annihilator could decimate a dozen AT-TEs, these droids struck fear into their enemies hearts, and played a major part in the Separatist victories at Palanhi and Formos.
In the Outer Rim Sieges, Republic commanders had to send a large number of clones to take out a single annihilator, causing the Republic to further curse the massive droids. However, they did not have a huge influence on the war's outcome.
Like all Confederacy battle droids at the end of the war, in 19 BBY, the annihilators were deactivated when the new apprentice of Darth Sidious, Darth Vader, sent the deactivation signal across the galaxy from Mustafar. However, the remaining annihilators, on the order of Emperor Palpatine, were taken in by the Imperial Department of Military Research. Some even became stationed at Palpatine's citadel on Byss.