A Doomsday Cannon is a devastating Necron weapon which is a wonder of that undying race's advanced technology, easily eclipsing the primitive directed energy weapons of the Imperium of Man. Only found mounted on a Doomsday Ark -- which is in itself nothing less than an enormous self-propelled Doomsday Cannon -- this is a weapon that can win a battle with a single shot. Even fired at low power, a Doomsday Cannon is a fearsome weapon; when firing at full effect, its searing energy beams burn many times hotter than more conventional Plasma Weapons. Infantry squads caught in the Doomsday Cannon’s fury are obliterated instantly whilst armoured vehicles are reduced to glowing slag. In the face of a shot from a Doomsday Cannon, nothing less than a Titan’s Void Shields can hope to offer more than a fool’s hope of protection.
As overwhelming as the Doomsday Cannon is, those who face it may find small relief in that the weapon requires immense amounts of energy to fire. Due to the energy constraints that are inherent in the design of a Doomsday Ark, a Doomsday Cannon can only be fired at full power whilst the vehicle is not moving. This is because the weapon draws on the same power reserves as the repulsor engines of the vehicle. Any systems not directly pertaining to the Doomsday Ark’s main armament are part of the motive units that power its anti-gravitic engines and propel it into position, or the shielding arrays that give the vehicle some measure of protection from enemy fire. Each of these secondary systems draws power from the same source as the Doomsday Cannon, and much of the pilot’s concentration is taken up ensuring that the energy distribution is appropriate to the tasks at hand. As a result, a Doomsday Cannon is somewhat less effective when fired during or immediately following any significant movement of the craft, due to the need for the pilots to redistribute power to the dimensional repulsor motive units that keep the Doomsday Ark aloft. This forces the Doomsday Cannon to receive less power and fire a weaker, though still powerful, blast. Then again, even a low-power blast from a Doomsday Cannon rivals the most hallowed of Adeptus Astartes Plasma Cannons for destructive potential.
- Codex: Necrons (5th Edition), pg. 48
- Codex: Necrons (7th Edition) (Digital Edition), pg. 198
- Deathwatch: The Outer Reach (RPG), pp. 139-140