Basically a Ghost Ark with a huge cannon underslung beneath it. The Doomsday Ark kind of got its idea of some Necron Lord or higher ups who thought that killing the primitive's tanks with their floating boats was so hilarious that it would be even better to modify said floating boats into a Necron self-propelled gun that can immolate their largest Titans. Just for the kicks.
According to our #1 Machine Molesters. Doomsday Arks are powerful enough to bring down an Adeptus Munitorum-standard M.39 “Scutum” prefabricated bunker in a single bombardment, a Doomsday Ark, when encountered, must be dealt with before it can move into firing position; for a single salvo can leave an entire army in ruins. Whatever personal eccentricities they might individually favor, all Necron Overlords hold an absolute belief in victory through overwhelming firepower. Some of the Necron‘s bitterest enemies have claimed this is simply due to the Necron’s android forms being somewhat less than impressive in swirling melee. However, the truth of the matter is that as flesh and as machine, the Necrons have ever won their wars through the unrelenting application of superior technology. As such victories are invariably won at a distance, all Necron battle codicils emphasise ranged superiority. Nowhere is this more evident in the Doomsday Ark; amongst the most feared of all weapons In the Necron arsenal.
On tabletop Doomsday Arks deals out big steaming helpings of FUCK YOU! in the form of S 10 AP 1 large blasts with 72in. range when it stays still or a S 8 AP 3 blast with 24 in. range if it moved, which is still nothing to sneeze at. Can reliably eat MEQS, TEQ and armoured vehicles for breakfast (when the scatter dice hits successfully)
It is a very good model to have on the deep end of the table, but if the enemy Deep Strikes anything dangerous too close to it, you better run away and let your troops do the clean-up - Don't let the supposed defensive Quantum Shielding fool you, it will go down if targeted properly.
Which brings us to one of the main problems of the Doomsday Ark; if it moves (or Jinks), it cannot benefit from the full power of the Doomsday Cannon, though even so it's still nothing to sneeze at. The other problem is that, while AV13 is durable, like all Necron-Skimmers it is also Open-Topped meaning AP1 weaponry can force the vehicle to explode on a 4+ or penetrate it and lose its Quantum Shielding. Still, if the deep striking fleshlings don't explode it in one shot this has 4HP to take hits for you.
In the old codex you could combine with a Triarch Stalker to fuck anything that you don't like (Granting twin-linking for the fucking thing), but the Stalker only benefits infantry now. Should its target survive just bring in the Doom Scythes or rush it with Canoptek Wraiths. Anything can pick up the mess of what's left of the enemy after this thing is done.
In conclusion this thing is just a massive sod off tool that is piloted by a drunk lad whom finds the annihilation of all living things a 'fun' hobby so S10 AP1 large blasts everything he sees in order to feast upon the tears of the opponent and make him hide. So always a nice, pleasant model to cheer up your day - feeling sad? blow up the bugger who made you sad (if you even play him) or just blow up another guy as a gesture of good will so that he promises never to pull out the god-forsaken Riptide again.
In 8th edition, Doomsday Cannon is D6 shots S10 AP-5 D D6 at 72in or D6 shots S8 AP-2 D D3 at 36in if moved. Combined with 14 PV and the Quantum Shielding, Doomsday Ark is a good support unit (it's outperform the fire prism against T7 to T9 vehicle).
|Forces of the Necrons|
|Command:||Cryptek - Destroyer Lord - Necron Lord - Necron Overlord - Phaeron|
|Troops:|| C'tan Shards - Deathmarks - Flayed Ones - Immortals |
Lychguards - Necron Warriors - Triarch Praetorians
|Constructs:|| Canoptek Spyder - Canoptek Wraith - Crypt Stalker |
Scarab - Tomb Sentinel - Tomb Stalker - Seraptek Heavy Construct
|Vehicles:|| Annihilation Barge - Catacomb Command Barge - Doomsday Ark |
Ghost Ark - Monolith - Sentry Pylon - Triarch Stalker - Tesseract Ark
|Flyers:|| Canoptek Acanthrite - Doom Scythe - Heavy Destroyers |
Necron Destroyers - Night Scythe - Night Shroud - Tomb Blades
| Abattoir - Æonic Orb - Doomsday Monolith - Megalith |
Necron Pylon - Obelisk - Tesseract Vault