The Gatling Cannon started out as a naval weapon, in the days dating back past the First Ienpokan Hegemony, used extensively first by the seafaring Empire of Dorrilea, prior to it's destruction at the hands of Basil Jubileus at the battle of Herr Tokos. It was nothing complicated; three barrels mounted on a rotating disk, each being packed with shot that was ignited when the barrel spun into place and touched a fixed flame to the wick. The disk was lined with handles and turned manually, locking into position when the loaded barrel was to make contact with the lit fuse. The whole contraption was mounted on wheels, so it could easily slide back on deck, without shaking itself to pieces. In this way, it could be spun and shot three times before having to be reloaded.
Upon the defeat of the Dorrileans at Herr Tokos, and their subsequent fall from power, the Ienpokan city state of Fiorlion began to include a complex version of this into their ships-of-the-line, transforming what were once simple gun-triremes, armed with no more than twenty cannons on the sundeck, into highly mobile attack frigates.
Because the tri-barreled cannon was really no larger than one, mid-sized cannon, it took up the same amount of space, while offering nearly three times the firing potency of one main gun. Better yet, it could be mounted forward facing because of their relatively small size:firepower ratio, letting the ship fire from a slender front profile, rather than shooting parallel to the attack ship. This was particularly advantageous when the ship came in at a perpendicular angle at ramming speed, where these "Gatling Cannons" could be used to fire forward while the ship gained velocity.
Much later, the Eretanians would utilize them in their short lived, but efferctive sea conquest against the Acarids, though with several major differences. The cannon barrels were not just paired in triangular "threes" now, rather the number of barrels went anywhere for six to ten, usually all small bore, or grapeshot. Larger triple-barrel cannons still existed, but saw minimal use in the Eretanian campaign against the Acarids. In the old ships, the pause was long enough for a crewman to load the shot manually, just in time for the empty barrel to snap up, and into firing position. Now, the barrels moved much more quickly, thanks to an automated firing system.
Ingeniously designed by an Eretanian engineer, the entire cannon was essentially a giant spinning steam-powered clutch, the barrels mounted on a locked fly-wheel, which would be forced back by the recoil of the firing cannon. The recoil sent the fly wheel backwards, making contact with the clutch, spinning the next gun upwards, then disengaging. The empty barrel would promptly spin downwards, at some point in the cycle picking up another round of ammunition from a gravity fed shot dispenser, where the entire round was neatly packed into an explosive pre-fabricated package.
This design did have it's fair share of fouls - the system from time to time, misfired as the inefficient clutch mechanism had a tendency to either miss cycles, or fail to ignite a charge, causing the barrels to become logged with more ammunition than necessary. This effectively turned the cannon into a deathtrap - a problem that conventional cannons always had, but which made Gatling Cannons exponentially more hazardous. The Eretanians would attest that the risk was undoubtedly worth the reward, as they shattered the Acarid Navy, who had been formerly top dog in the seas of Eastern Greatland, utilizing old Ienpokan Tri-Barrel designs mounted on Gun-Triremes.
Ramming and boarding was a large part of Ienpokan naval doctrine, which had naturally translated into Acarid Naval doctrine. The Eretanians, on the other hand, favored lighter ships, smaller bore guns, and an emphasis on using small arms fire to pick off crew at a distance rather than boarding. With the rapid firing Gatling Cannon and their long, agile Clipper style ships, they could both outrun and dodge the Gun-Triremes as they came in to ram, while laying down a heavy rain of splintering fire that would rip oarsmen or marines on deck, to shreds.
Learning from their mistakes, the modern day Acarid navy, in the absence of the Eretanian Empire has become prominent in the east seas once more, utilizing more effective and efficient Gatling Cannons, reinventing the old, large bore tri-barrel cannon as heavy ordinance weapons, supplemented by the smaller, rapid fire Eretanian Style Gatling Cannons. They are a common sight on most sailing vessels, though they are still considerably less numerous than standard cannons which may be mounted on either the top deck of small ships, or on the gun deck of ships-of-the-line. Greatlanders as a whole, are not of a seafaring culture, and indeed, most ships are used as a simple means of transportation rather than naval warfare. Ienpokan city states that lie in coastal areas still rely heavily on naval supremacy or at least naval competence, when Acarid Privateers and Corsairs under the employ of certain Acarid Naval Dignitaries are an ever present threat.
Besides Acary and Ienpokos, the only Naval Power in Greatland might be the Caernian "Navy" though calling it such might be an overstatement. The Caernian Channel-Guard, the small naval contingent that watched the channel between the mainland and the isle is well equipped, but lacking in numbers, though they easily quash the Caspernian competition which boasts little to no naval power at all. The coastal Zuudi states as well as Teutonian Sea-Lords have began to see the importance of a strong Navy as Acary explores her western boundaries.
But the sheer power and performance of the Gatling Cannon is not wasted away on land-lubbing Greatlanders. In true Greatland fashion, they have found a terrestrial use for it, employing it in the good-old-fashioned alternative to ships; heavy armor.
The Steamtank was invented (though more likely "reinvented" or "rediscovered") sometime shortly after the close of the Age of Night. There were a number of both civil and martial applications for such a powerhouse of horsepower. Sir Germund Freyr of Ottindar, Teutonia, was the first to mount a Gatling Cannon on a Steamtank Frame. At the time, tanks were relatively small - no larger than a simple peasant's hovel, mounted on steel tracks, so the bore was fairly small and it was only highly effective against targets wearing carapace armor or less. It soon became completely ineffectual against Knights in powered armor, who would be able to shrug off the rounds like Beebees launched from an Air Rifle.
Over time, however, this changed. Tanks got bigger. Much bigger. The largest, up to ten times as big as the original model that Sir Germund Freyr van Ottindar had designed. The Caspernian "Majesty Mk.II" sports up to four Quad-Barrel Gatling Cannons with large, rifled bores, magazine loaded ammunition, jacketed artillery rounds, and is fixed to the hull of the tank. These are just the icing on the cake, being complimented by the explosive power of the main gun, two to three Coaxial mounted Thumpers or Stompers and a pintle-mounted Archbalest. From the Gatling Cannons alone can be launched a wall of steel, each gun firing forty rounds a minute, which may seem excessively slow when compared to a Thumper's admirable sixty round-per-minute sustained fire rate, but considering the cannons fire a round ten times larger than the average Thumper or Stomper slug, is is impressive none the less.
While wheels work fine on a boat, where space is relatively ample, the space inside even the most massive battle tank is still cramped. To make up for this recoil, the barrels slide back towards the clutch on rails, and the clutch is padded and reinforced to absorb any extra trauma that may come from sustained fire. Excess shock to the frame's integrity is absorbed by a number of complex weighted dampers and springs. Motion is only one way (the Gatling cannons are fixed, and they do not pivot.) A single Gatling Cannon may not break apart a Knights Powered Plate with one blow, but sustained fire downrange is powerful enough to break away at mithrilized metals. Multiplied by Three other simultaneously firing Gatling Cannons, timed on a belt-clock and synchronized clutch wheels so that at least one is ALWAYS firing, the Gatling Cannon makes for an impressive ally and a dreadful foe.
This makes for a terrifying weapon, both in terms of breaking morale and personnel. It is not, however a true cannon, at least not anymore. It has in some sense, lost it's use as an ordinance weapon. The Jacketed, bullet shaped rounds excel at taking out light fortifications, chipping away at heavy armor, and literally turn unarmored organic material into a fine red mist, but it lack stopping power against permanent fortifications or siege defenses. The main-gun of the modern Battle Tank (dubbed the Author Walther Gun, being invented inadvertently by an Author of the Ark,) is another story, but for another time.
The tank, and it's supporting guns are perhaps, one of the pinnacles of Greatlander engineering. The Gatling Cannon and it's various evolutions are a testament to the fact that an old dog can be taught new tricks. From it's humble origins on the ships of Dorrilea, to it's first amphibious journey onto land in the Sir Germund Freyr Tank, to it's most recent debut in the Caspernian Style "Majesty Mk. II" the Gatling Cannon has gone through many changes and additions, all of which have proved time and time again the versatility and tenacity of this archaic weapon, with newfound purpose.