What do Grots do when they're not being prodded towards the front lines, used as food, clearing mine fields, or running through enemy fire to bring supplies?
Mek Gunz are the product of... well, Meks that make giant-ass guns! Meks love making bigger and killier weaponry, and sometimes they come up with weapons that just aren't man (er, ork) portable, even by the most muscle-bound of skarboy Nobs. These weapons are generally fit for mounting on a Gun Trukk, Battlewagon, or even a Stompa! Sadly, many meks can sorely lack a momentous-enough Waaagh! to have a healthy supply of war-machines needing said big-ass guns. Instead, many less well-to-do mekboys strap their terrifying creations to overburdened wagons or spare trukk-wheel axles, park them in the back-lines, and launch volleys of random artillery-fire at unsuspecting foes.
This un-Orky job of sitting away from the front lines, not beating someone's head in, is given to Grots. This is actually a grand job for said weedy goblinoids, as they love nothing more than not being beaten senseless by their ork overlords (who are busy beating someone else for a change!). Unfortunately, many of these guns are less than reliable. You see, once a mekboy has had their fill of standard powder-and-shell weaponry, they will take to the time-honored art of MAD SCIENCE! and craft all manner of death rays, tractor beams, and assorted energy weapons. Regrettably, many of these fancy "Mek Gunz" are less than ready for prime-time, and many grot crewmen will most likely die due to their own weapons backfiring on them. It's a Grot's life, but it's all in the name of science, of course!
Interestingly, they're also favoured by the otherwise technologically-backward Snakebites clan. This is less due to them liking heavy artillery and more to the fact that their Boyz don't bother with sophisticated weaponry and so any they loot is given to the Grots to figure out what to do with it.
On the Tabletop
Go check out the Ork Tactics page for more reliable, specific, and up-to-date information on how to properly field Big Gunz and Mek Gunz.
Until recently, the only orky artillery that existed were Big Gunz. These are the old "standard 3" too-big-to-carry heavy weapons: Kannons, Lobbas, and Zzap Guns. These are actually Imperial Guard Heavy Weapons Team analogs. See, back in the day Games Workshop balanced the initial run of 2nd Edition and 3rd Edition rules by having easy analogs for every weapon across all of the races. The Kannon is a Missile Launcher, the Lobba a Mortar, and the Zzap Gun is a Lascannon. It was that easy.
These guns could be found on all kinds of things, from towed artillery to Looted Wagons and Battlewagons, all the way up to secondary batteries on Gargants, Battle Fortresses, and Battlekroozas (the space and naval varieties). While this is still true to this day, when many players think of Big Gunz they think of the artillery pieces.
Since all Gunz are manned by Grots, they all have BS4+ (the new BS3), and they also still benefit from the Dakka Dakka Dakka rule. This results in approximately a 58.3% hit rate, which is amazing for Orks.
The old Big Gunz
As of this writing late in 8th Edition, the Big Gunz miniatures are now OOP and the units themselves have also been retired from the Ork Army list. However they are still available for use in friendly games as a Legends entry, or occasionally as a weapon option on certain Ork vehicles.
- Kannon: Exactly what you think they are. Except not. Kannons come in all shapes, sizes, colors, and calibers, but most common of all designs is the short-barreled, high-caliber breech-loader. The kannon actually serves the same function to Orks as the Missile Launcher does to the Imperium, capable of firing a solid shell or penetrating explosive for vehicle busting, or a canister shot or fragmentation shell to tear up infantry. Too heavy to be carried by even an Ork, these metal beasts are usually mounted on vehicles or artillery wagons, and have a longer reach than the man-portable Rokkit Launcha. In Gorkamorka, kannons were an ork-portable weapon roughly comparable to a orky elephant gun, but nowadays those weapons are called shoota-kannons. On the tabletop, a Kannon was known as Old Reliable. In the hands of a Grot crew, it was the most flexible of the Big Gun choices. In 8th Edition, it exists primarily as a weapon option for the Gunwagon.
- Lobba: Essentially a big metal pot jammed with gunpowder and a bomb, usually in that order. The Lobba serves as an Orkish mortar, and is favored by Grot artillery crew for being able to kill things without the enemy having to see you. The huge recoil it generates (beyond even the overblown Kannon) relegates it to being mounted (securely?) on vehicles or towed artillery platforms. It is powerful, but most armor will deflect its blast. Crunch-wise, it is a good anti-infantry weapon in an army full of anti-infantry shit. Holy hell, a battery of these parked behind a building could go to town on Blobguard. In 8th Edition it lives on as a weapon add-on for the Battlewagon.
- Zzap Gun: A unique piece of technology crafted by energy-loving Mekboyz, a Zzap Gun is a rough analog to a Lascannon. Roughly. The gun consists of a metal barrel covered in wires, a capacitor, and a power source. The crew use a lever (which electrocutes the user) to determine the charge built up in the capacitor before firing a literal lightning bolt at the target. The gun defies all known physics, and the power supply is so heavy that it must be mounted on something sturdier than a pair of green legs. The unpredictable effectiveness of the weapon deterred some Warlords from using it, but if Lady Luck smiled, in earlier editions it was possible to take down a Land Raider with one. In 8th Edition this weapon is now a relatively minor threat to most vehicles. This is because the Zzap Gun randomly rolls for Strength, which makes it highly unreliable, even for Orks. And while 8th edition removed the worst side effects of the Zzap rule, the weapon is maxed out at 3 points of damage per hit. And yes, those can be converted into 3 mortal wounds if you roll an 11 or 12 for the shot's strength, but then your vehicle also takes a mortal wound in return. It's no surprise that Zzap Guns are almost never seen in Ork armies anymore, not even on Gunwagons, because what used to be merely Un Poco Bueno is now majorly No Bueno.
The new Mek Gunz
7th Edition introduced four new shootier, flashier, and much larger big guns, called Mek Gunz. Mek Gunz were a Gork/Morksend in 7th edition, and they remain excellent in 8th! Like the Big Gunz before them, Mek Gunz are sometimes found on other Ork vehicles as powerful ranged weapons. The Wazbom Blastajet, for example, has a Smasha Gun, and both the Blastajet and the Morkanaut carry variants of the Kustom Mega-Kannon.
- Kustom Mega-Kannon: The kustom mega-kannon is essentially a much bigger version of the Kustom Mega-Blasta and is the Ork equivalent of a Plasma Cannon. This profusion of worky gubbinz and zappy bits works as a potent anti-tank weapon, but is just as unstable as its smaller cousin because it cannot be fired on low power. Overall it is a reliable source of S8, AP-3 shots that will shred though armor and probably not kill itself over the course of your game. However this is also the most expensive Mek Gun at 65 points, and it is somewhat limited by its 36" range.
- Bubblechukka: The Bubblechukka is an example of force field technology that has been weaponized by Orks rather than being used for protection. It fires unstable force bubbles at the enemy that explode on impact. They vary wildly in size and solidity, some fly like meter-wide boulders that hit with a negligible strength, whilst others float down like small soap bubbles and, after bursting, inflict horrible damage. Here we have the oddest choice in our arsenal. It is a highly variable weapon that can be shockingly effective at destroying heavily armored infantry (like TEQs), but at the same time is nearly as likely to have little effect. 50 points is a bit high for this weapon, especially with a 48" range.
- Smasha Gun: A miniaturized Lifta-Droppa gone all wrong. Another odd choice, playing somewhat like a bizarro Zzap Gun. It fires D3 shots, but in order to wound you must roll equal to or higher than the target's toughness on 2d6. Each success does D6 wounds with AP-4. Along with the Shokk Attack Gun or the occasional killsaw this is one of the few Ork weapons that can auto-penetrate all but the heaviest armor. While it can effectively engage vehicles if needed, due to the randomness inherent in this weapon it is best used for taking out TEQs or other heavily-armored infantry, especially when you can mass fire from several Smashas. Happily, this is the cheapest Mek Gun at only 40 points, and it is also blessed with a 48" range. As such it is virtually an auto-include in most Ork armies.
- Traktor Kannon: An example of Orks weaponizing tractor beam technology, the Traktor Kannon is basically a smaller Lifta-Droppa, but an actually functional one! Hell yeah! Its main function is to literally rip aircraft out of the sky and smash them into the ground. This Gun gained a reputation for being the best anti-flyer weapon in the game back in 7th Edition, and it's still quite effective in 8th Edition. In 8th, the Traktor Kannon automatically hits its chosen target with a single S8 shot at AP-2 doing D6 wounds. If the Traktor Kannon targets and destroys a flier, that flier automatically crashes and burns. Considering what it does, 50 points is a reasonable price for this weapon and the 48" range is an added bonus.
When Warhammer 40,000 was rolling around in it's 2nd Edition toddler years, it was heavily influenced by other British tabletop games of the era, including WWII-era ground combat games. Rick Priestley himself has gone on to make Bolt Action at Warlord Games in recent years. Orks have always had a bit of the German Wehrmacht in them, from their early-years "Hun" helmets to the propensity to call everything a "wagon" (Looted Wagon and Battlewagon are riffs on the german Panzerkampfwagen, literally "armoured combat vehicle").
The fact that weapons like the Traktor Kannon parallel the well-known German 8.8 cm Flak gun, and how it was used in a dual-purpose role (anti-tank and anti-aircraft) during WWII is no coincidence.
The more you know.