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

Autocannons ranged in caliber from 30 mm up to 203 mm and were loosely grouped according to their damage against modern armor. The exact same caliber of shell fired in a 100-shot burst had a shorter effective range than when fired in a 10 shot burst, due to recoil and other factors. Autocannon were grouped into the following loose-damage classes:[1]

Beyond the "standard" models, variants included the shotgun-like LB-X, quick-firing ultra, and the gatling-type rotary. Light-weight variants and capital ship-scale models also existed. The experimental hyper-velocity autocannon also entered limited production.[2][3]

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.[4] 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.[5] They could only carry three-quarters of the ammunition per ton, compared to modern autocannons.[5]

Standard autocannons could be tweaked by a technician to double their rate of fire, similar to an ultra autocannon; however, this carried significant risk. Forcing an autocannon to fire at double its normal firing rate could jam the weapon. In the worst case, this caused detonation of the ammo in the cannon itself, destroying the weapon, as well as likely damaging the internal structure of the mount location.[6]


Classes of autocannons were not standardized by the caliber of the individual weapon systems' barrels. Autocannon in a class varied by manufacturer and model. With the number of shells and caliber being specified, no autocannon has been described as firing one shell fired for each "round" or burst of fire. One possible exception, the 210mm ultra autocannon/20, was sometimes found on the Gargoyle C and Cauldron Born A OmniMechs. Other possible exceptions included the Defiance Killer AC/10, as mounted in the Hatchetman, and possibly Federated autocannon/10 on the Enforcer.[citation needed]

Barrel Arrangement[edit]

All rotary autocannons were multiple-barrel arrangements.[1] Some standard, light, and ultra autocannons also used a multiple-barrel arrangement, though not as frequently.


  • 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. 118, "Prototype Dates For Basic Weapons Table"
  5. 5.0 5.1 Interstellar Operations, p. 118, "Primitive Prototype Equipment Rules"
  6. Tactical Operations p. 100 "Autocannons"