The Annihilator Beam is a giant FUCK OFF weapon used as the primary armament of the Triarchal Menhirs.
It is unknown what this weapon is exactly, is it a juiced-up Gauss weapon or a Doomsday Cannon on steroids? We have no idea, what we do know is that the Annihilator Beam has one of the most appropriate sounding names, 'cause this monster annihilates anything standing in its way. Seriously, Baneblades and Land Raiders would role for critical existence failure once these things are on the battlefield.
Crunchwise, it's like the fluff. This thing is a fucking monster on the tabletop. S12, AP-4 and a flat 6 Damage per hit. The Annihilator Beam will bore a hole through the rear ends of your tanks. Its 36" range makes it incredibly dangerous at mid-to-close range whilst the fact that there are always TWO Triarchal Menhirs, means that not only can they attack independently, but if they combine their attacks, there goes 12 Wounds in a round. These things are not to be fucked with.