The Assault Cannon is a ballistic six-barreled, self-loading rotary Autocannon, effective against infantry targets and light vehicles at close to medium range. It is a medium calibre rotary Autocannon, with its 6 barrels cycled by an electric motor past a single chamber. The Assault Cannon was developed after the end of the Horus Heresy in the early 31st Millennium as a replacement for the Autocannon. Introduced during the Mark IIIA phase of Indomitus Pattern Terminator Armour development, this weapon is the standard alternative to the Heavy Flamer as a Terminator Squad's special ranged weapon. Its design has changed little in 10 Terran millennia, retaining the distinctively long, cylindrical, rotating barrels. Although it lacks the range of the Autocannon and many other Imperial heavy weapons, the Assault Cannon is a fearsome weapon when used at the close range role from which it was intended to be fired. The weapon is prone to overheating and jams due to its high rate of fire -- the number of rounds fired per second are counted in the hundreds. The barrels and other firing components are made of a heat-dispersing ceramic/metallic alloy, helping the weapon to withstand the intense heat generated by its high rate of fire. Despite this, the barrels still reach temperatures of over 300°F. Due to the high rate of wear on the barrels, the barrels are usually replaced after every mission by most Space Marine Chapters and Imperial Guard regiments that use the weapon. Motor and barrel failure are common problems with the Assault Cannon, making the weapon prone to jamming during sustained bursts. The weight and complexity of its mechanism, and the heavy recoil generated by its fire means that the Assault Cannon requires a stable firing platform to be unleashed effectively.
The weapon's large size and tremendous fire rate require a special means to sustain, so the Assault Cannon is normally mounted on Imperial vehicles or combat walkers such as Sentinels and Dreadnoughts, or specially damped and fitted to Space Marine Terminator Armour. It is also commonly used by the Blood Angels Space Marines as their close-assault Baal Predator main battle tanks sport a twin-linked Assault Cannon in the turret. The anti-infantry Land Raider Crusader also has a similar dual Assault Cannon mount (whilst the standard Land Raider has a dual Heavy Bolter). The Razorback has the option to use a twin-linked Assault Cannon. Although the Assault Cannon lacks the range of other rapid-fire ballistic weapons such as the Heavy Bolter and the Autocannon, its enormous rate of fire enables it to literally shred its way through most targets, punishing them with a hundred rounds per second. Assault Cannons are extremely potent at medium-to-close range, against armoured infantry and moderately armoured vehicles, while Heavy Bolters are only effective against lightly armoured targets. However, Autocannons have a slower firing rate than a Heavy Bolter. The Assault Cannon epitomises the deadliness of elite Terminator Squads who teleport behind the enemy's front line and open up with fully-automatic fire, spreading carnage and terror. Assault Cannons are used by Planetary Defence Forces on rare occasions as a stand-mounted defensive weapon, and are also found on the Destroyer variant of the Marauder bomber.
The weapon is not considered man-portable, however the powerful servos, recoil compensators and stabilisers built into Terminator Armour allows the elite Astartes Terminator Squads to carry the weapon into battle. The Assault Cannon is well-suited to the battlefield role of Terminator Squads, providing a massive rate of fire which often compensates for the enemies' vast superiority in numbers. In confined environments providing long corridors of fire, such as Space Hulks and the hive cities of Hive Worlds, the Assault Cannon is invaluable. The high rate of fire makes the Assault Cannon unsuitable for extended engagements when used by Terminators, as the ammunition carried is quickly exhausted. This drawback is negated in vehicle and Dreadnought mountings, where ammunition storage capacity is far greater. The standard ammunition fired by an Assault Cannon is a cased round, comprising a dense metallic core covered in a non-metallic composite sheath with a diamantine tip. This provides excellent penetration capabilities against light and personal armour. It has long been reported by the Astartes that the Assault Cannon's massive rate of fire can allow it to chew through armour that would normally be impenetrable to a weapon of its calibre. Extensive testing by the Adeptus Mechanicus supported this observation, and Adeptus Astartes targeting doctrines have been officially amended to recognise this attribute. In general, the logistic shortcomings of the Assault Cannon are far outweighed by its destructiveness in combat and its effect on enemy morale.
Notable Assault Cannon Patterns
- Mark II Absinia Pattern Assault Cannon - This pattern of Assault Cannon is known to be used by the Red Brethren Terminators of the Carcharodons Chapter.
- Mark VIII Absolo Pattern Assault Cannon - This pattern of Assault Cannon is the one most often deployed by Space Marine Terminators and other Space Marine forces like Dreadnoughts and Land Speeders.
- Iliastus Pattern Assault Cannon - This prototype weapon system was designed as a more compact and portable variant of the highly successful Kheres pattern. It was, as can be divined by its pattern designation, first developed on the Iliastus Satellite in the Sol System by the Dyzanique techno-esoteric cult. This was a secretive organisation whose fealty to the Emperor predated his alliance with Mars. Under field testing with the VII (Imperial Fists) and IX (Blood Angels) Legions before the outbreak of the war of the Horus Heresy, the Iliastus pattern evidenced formidable firepower, but was prone to catastrophic failure under the rare conditions of heavy use.
- Kheres Pattern Assault Cannon - The Kheres Pattern Assault Cannon is an ancient pattern of the weapon that was commonly deployed on Contemptor Pattern Dreadnoughts during the Great Crusade and the Horus Heresy. It maintains a higher rate of fire than the standard pattern Assault Cannons used in the late 41st Millennium.
- Nomus Pattern Rotor Cannon - The Nomus Pattern Rotor Cannon is the ancient predecessor of the modern Assault Canon. It was commonly used amongst the newly-established Terminator-armoured elite veterans of the various Space Marine Legions during the Great Crusade and Horus Heresy eras during the 30th and early 31st Millennia.
- Codex: Blood Angels (5th Edition), pp. 56, 59
- Codex: Space Wolves (5th Edition), pg. 59
- Warhammer 40,000 Rulebook (6th Edition), pg. 54
- The Horus Heresy - Book One: Betrayal (Imperial Armour), pg. 239
- The Horus Heresy - Book Two: Massacre (Imperial Armour), pg. 104
- The Horus Heresy - Book Three: Extermination (Imperial Armour), pg. 267
- Warhammer 40,000: Compendium (2nd Edition), "Terminator - Space Marine Tactical Dreadnought Armour in Warhammer 40,000", by Rick Priestley & Andy Warwick, pp. 12, 15
- Warhammer 40,000: Rulebook (3rd Edition), pg. 61
- Warhammer 40,000: Wargear (2nd Edition)
- White Dwarf 112 (US), "Terminator: Space Marine Tactical Dreadnought Armour in Warhammer 40,000", by Rick Priestley & Andy Warwick, pp. 12, 15
- Carcharodons: Red Tithe (Novel) by Robbie MacNiven
- Tales of Heresy (Anthology) edited by Nick Kyme and Lindsey Priestley, "Scions of the Storm" by Anthony Reynolds, pg. 207