While some variation exists, the basic design of a Nova Cannon consists of an array of gravimetric impellers which accelerate a projectile to a fraction of the speed of light.[2a] However, Nova Cannons can only be mounted on large capital ships such as Cruisers and Battleships and in the ship's prow.[2a] This is because the immense recoil of firing the weapon can only be compensated for by the vessel's engines.[1c] While at least one Astartes Battle Barge is known to have been retrofitted with a nova cannon, doing so taxed the vessel to its limits: firing the weapon resulted in momentary power failure throughout the ship.
The projectile itself varies in greater design and size, ranging upwards of fifty meters in diameter. However, all share the common goal of causing immense destruction across thousands of kilometers of space. These can range from sophisticated plasma warheads which burn with the ferocity of a small star for a fraction of a second to implosion devices which exert destructive gravitational forces.[2a]
Because of the destruction it can cause over a vast area, a Nova Cannon projectile is not armed until a fraction of a second after firing, though by that time it will have already traveled tens of thousands of kilometers through space.[2a] Nova Cannons are also notoriously difficult to operate and inaccurate, which is why many Naval captains prefer to use traditional torpedoes instead. For those captains which do mount them, a well-used Nova Cannon can be a terrifying weapon and psychological tool.[2a]
Mars-pattern Nova Cannon
The Mars-pattern Nova Cannon is the most common of all Nova Cannon construction templates. Colossal weapons measuring hundreds of meters in length, they fire a gigantic shell at near relativistic velocities. The shell mirrors a conventional explosive shell, although on an extremely massive scale, and upon detonation will explode with more force than dozens of plasma warheads.[2b]
Ryza-pattern Nova Cannon
The Ryza-pattern Nova Cannon replaces the explosive shell used by the Mars-pattern Nova Cannon with a highly unstable plasma-based macro-bomb. These weapons use much more power than a Stygies-pattern, but are thought to be more effective. Weaponising such a huge quantity of plasma however carries its own risk, as overheating systems can potentially cause damage to the weapon and the ship itself.[2b]
- Doppler Shells - Release large amounts of graviometric waves that will bounce off the hulls of ships and expose hidden enemies.
- Electromagnetic Shells - Designed to interfere with enemy sensors and communications.
- Grav Shells - A newer design, these are extremely difficult to make and as such are extremely rare and dangerous. When detonated, Grav Shells implode in on themselves and create a miniature black hole.
- Rift Shells - Similar to a Vortex Torpedo, except much larger.
Known ships equipped with Nova Cannons
- Ark Mechanicus[5a]
- Apocalypse Class Battleship
- Victory Class Battleship[5b]
- Mars Class Battlecruiser[1a]
- Mercury Class Battlecruiser[5b]
- Dominator Class Cruiser[1b]
- Alcazar Remembered - A Battle Barge of the Fists Exemplar, ca. 544.M32 (retrofit).
- Oberon - An Ordinatus.
- 1: Battlefleet Gothic Rulebook
- 2: Rogue Trader: Battlefleet Koronus
- 3: Warriors of Ultramar (Novel), Chapter 5
- 4: Planet Killer Magazine #1, pgs. 31-33
- 5: Battlefleet Gothic 2010 Compendium
- 6: Battlefleet Gothic Armada, pg. 12
- 7: The Hunt for Vulkan (Novel), Chapter 4
- 8: Helsreach (Novel) - Armageddon (Anthology), Chapter IX