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An autocannon is a type of rapid-firing, autoloading direct-fire ballistic weapon, firing high-explosive, armor-defeating rounds at targets in bursts. They are, basically, giant "machine guns" that fire predominantly cased-explosive shells, though models firing saboted, high-velocity kinetic, energy penetrators and caseless ordnance do exist. Among the earliest modern tank/BattleMech-scale weaponry produced, autocannons generate far less heat than energy weapons, but are considerably bulkier and dependent upon limited stores of ammunition.

Autocannons range in caliber from 30 mm up to 203 mm and are grouped according to their damage against modern armor. With these loose guidelines in mind, autocannons are divided into the following classes:[1]

Beyond the "standard" models, variants include the shotgun-like LB-X, quick-firing Ultra, the gatling-type Rotary, and the ProtoMech Autocannons. Light-weight variants and capital ship-scale models also exist. The experimental hyper-velocity autocannon also entered limited production. [2][3] Another interesting variant was the so-called Improved Autocannon of the early Clans. Being slightly lighter and slightly more compact than equivalent standard autocannons, Improved Autocannons served as a stepping stone toward the development of Clantech LBX and Ultra ACs. By the time of the Clan Invasion Improved Autocannons were obsolete. [4]

Early "Prototype Autocannons" were made as a progression forward from the rifle found on early tanks of Terra. The first AC/5 system was prototyped in 2240; the AC/2 came along later, with the first prototype debuting in 2290. The AC/10 system was prototyped over two hundred years later, in 2443. The AC/20 was first developed in 2490.[5] These prototypes were largely similar to modern autocannons, but they had rare tendencies to jam, locking up the weapon for the duration of the rest of the battle.[6] They could only carry three-quarters of the ammunition per ton, compared to modern autocannons.[6]

Standard autocannons can be tweaked by a technician to double their rate of fire, similar to an ultra autocannon; however, this carries significant risk. Forcing an autocannon to fire at double its normal firing rate can jam the weapon. In the worst case, this causes detonation of the ammo in the cannon itself, destroying the weapon, as well as likely damaging the internal structure of the mount location.[7]

Discussion of caliber, barrel arrangement, and shells fired[edit]

Generally speaking, autocannons are not standardized by the actual caliber of the individual weapon, the number of shells fired, or even by the number of barrels they use. These descriptions can vary widely according to source material even when comparing weapons of the exact same type. However, TRO portraits and descriptions occasionally provide some insight into each weapon's configuration. Most autocannon are described as using a rotary arrangement to fire a burst, and larger weapons almost always have a correspondingly larger caliber. However, there are exceptions. For example, Ultra Autocannons are often, but not always, described as rapidly firing single shells from one barrel. Likewise, LBX autocannons using standard shells are usually described as firing single shots. On the other hand, standard autocannons and light autocannons are usually described as using a multi-barrel arrangement, but not always. All rotary autocannons are explicitly multi-barrel arrangements, however.[1]


  • This article refers to a common object and addresses the object as a common noun. The preferred term is "autocannon" (except on section titles & table headings, where "Autocannon" is favored). When addressed by class, the preferred term is "autocannon/5" (et al), though is favored as "Autocannon/5" in section titles & table headings.


  1. 1.0 1.1 TechManual, p. 207, "Autocannon"
  2. Tactical Operations, p. 285, "Autocannons"
  3. Experimental Technical Readout: Mercs, p. 8, "Warrior HX-9"
  4. Interstellar Operations, p. 90, "Improved Autocannon"
  5. Interstellar Operations, p. 118, "Prototype Dates For Basic Weapons Table"
  6. 6.0 6.1 Interstellar Operations, p. 118, "Primitive Prototype Equipment Rules"
  7. Tactical Operations p. 100 "Autocannons"