Magnetic Accelerator Cannon

A MAC round fired from space as part of orbital bombardment.

Nils Thune: "Space? Those things even make noise in zero-gee?"

Ponder: "If you’re inside a MAC ship when the cannon fires? I don’t know if you’re a religious man, Governor. But it’s a little like a church bell—"

— Governor Thune and Captain Ponder discussing MACs.

The magnetic accelerator cannon, also referred to as a mass accelerator cannon or MAC, is a type of heavy weapon system employed by humanity, primarily the spacecraft of the United Nations Space Command. Within the UNSC, MACs are defined as a heavy weapon that fires a sizeable ferric-tungsten round at supersonic velocities from the bow of a capital ship, orbital defense platform or mounted driver emplacement. MACs are coilguns employing Asynchronous Linear Induction Motor (ALIM) technology and are typically used in military applications, though similar technology can be used in civilian mass drivers for industrial use.

Overview

MACs are fitted as a standard armament on most UNSC Navy vessels, ranging from small Gladius-class corvettes to Marathon-class heavy cruisers and even carriers or refit civilian ships such as the Phoenix-class colony ship. With a handful of exceptions, MACs are typically spinally-mounted, meaning that the entire ship is built around the gun, with the cannon running a significant portion of the ship's length. However, the technology is not exclusively used in spinally-mounted MACs, with naval autocannons (themselves sometimes referred to as "Mini-MACs") and even ground-based weapons such as the M68 Gauss cannon and M99 Stanchion operating on the same principle.

Operation

An animation of a coilgun's operating principle.

MACs operate on the basis of a coilgun. When firing, a series of stacked coil motors are sequentially activated, propelling a projectile with vast amounts of kinetic energy. The construction of the weapon takes the form of a series of coiled conducting wires (or solenoids). When a solenoid is activated, the projectile is attracted to the coil. As the projectile reaches the coil, a second coil is activated, attracting the projectile further down the barrel of the gun. This process is repeated as the projectile travels the length of the gun, with each successive solenoid accelerating the projectile to higher and higher velocities. As such, the longer a MAC's length is, the faster the muzzle velocity of the fired projectile.

This process differs from that of a railgun - a similar weapon system that feeds electrical current through a projectile to accelerate it along two conducting rails. Nonetheless, railgun weapon systems are occasionally referred to as MACs - as in the case of the Mini-MAC armament of the M510 Mammoth.

To fire a MAC, UNSC ships must draw power from the fusion reactor into a series of capacitors, storing the generated energy for firing. As such, charging the MAC draws power away from other sub-systems such as engines. As such, a MAC can be pre-charged and fired when ready, though at the cost of power to the aforementioned systems. Without the charge being maintained, the charge level does deteriorate. However, MACs can be fired at lower charge levels than 100% though likely to lesser maximum velocity. Likewise, firing the weapon at lower charge rates would also allow the weapon to fire more often if needed.

Ammunition

MACs are capable of firing a wide array of munitions, depending on bore and model. Some MAC rounds are extremely dense and constructed of ferric tungsten, noted by Captain Wallace of the frigate UNSC Commonwealth as a "heavy round". In the case of the MACs fitted onto the refit-colony ship UNSC Spirit of Fire, the rounds fired from its MACs are "low-mass" or consist of three-hundred-ton depleted uranium slugs. The MAC of the Spirit of Fire was later modified in a special project conducted by Ellen Anders, resulting in a specialised MAC capable of firing rounds that emit an EMP upon impact. Other munitions that can be fired from MACs include semi-autonomous drone missiles and for the larger 27 metre guns of UNSC Infinity, even include cargo pods and small spacecraft. A special kind of MAC round fired by the refit-UNSC Pillar of Autumn was composed of a ferrous core and an outer layer of tungsten carbide, which allows the round to splinter on impact with an enemy vessel, similar to the shredder rounds fired by an assault rifle.

Due to this variation, the masses, velocities and sizes of MAC projectiles can vary, ranging from 10 metre-long, 160 ton models fired by frigates and cruisers, to 600 ton depleted uranium models fired by Paris-class heavy frigates up to 3,000 ton projectiles accelerated to "point four-tenths" of the speed of light by the orbital defense platforms above Reach. The MACs of UNSC Infinity are additionally capable of firing various "sub-caliber" munitions for its massive twenty-seven metre bore, alongside some of the special types mentioned prior. MACs generally have a range of 10,000 miles (16,093 kilometers).

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  A slug fired by Cairo Station's massive "Super-MAC" gun.

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  A cross-section of the MAC found on Cairo Station.

Usage

Battle Group X-Ray firing their MACs at a Rasus-pattern interdictor.

"MAC rounds? In atmosphere?"

— Jorge-052 exclaiming his alarm at the intent to fire the MAC of UNSC Grafton during the Fall of Reach.

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As some of the largest and most destructive weapons available to humanity, their use is primarily constricted to space warfare. Most UNSC spacecraft are equipped with some form of spinal MAC, requiring the vessel to manually turn and face the target it wishes to fire on. MAC rounds are often fired in concentrated volleys by fleets of coordinated warships, and used as a long-ranged weapon for "sniping" enemy ships out of the sky. During the war against the Covenant, human MAC volleys were often fired in concentration, aiming to overload a target ship's energy shielding.

Atmospheric use and orbital bombardment

In select circumstances, MACs can be employed in atmospheres or for the purposes of orbital bombardment. Such orbital bombardment can be deployed against large targets such as enemy warships or bases, or against targets as (relatively) small as a Scarab. During the Battle for Arcadia, the UNSC Spirit of Fire made liberal use of up to forty MAC strikes in rapid succession to destroy a Covenant staging area near the Arcadia ONI facility.

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  UNSC Grafton fires its MAC at Spire One.

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  The frigates of Battle Group Victory fire their MACs at Anodyne Spirit - to negligible effect.

MAC classifications

MACs operate under a complex designation scheme composed of three primary naming components;

• MAC model number - the serial number designation for the specific MAC in question, composed of six alphanumeric characters consisting of two digits followed by a letter, a digit, another letter, and a final digit. The model number refers to the entire MAC assembly; in smaller vessels this applies to just the singular gun, in larger vessels it may be used to refer to the entire MAC battery. When used to refer to a MAC battery as a whole, the individual guns appear not to have any individual designations. The precise method for naming MAC models is unclear and does not have any outwardly-obvious sequential numbering or correspondence to the target ship(s) in question.
  • Example: 45J3D3
• Mark designation - Marks seem to be overall MAC generations, though the relationship of these weapons does not fully-line up with the years of introduction for the individual ships.
  • Example: Mark IX
• Size - this category denotes the overall size of the MAC, with the classifications of Light, Heavy, and Superheavy in use. The term "mini-MAC" is also sometimes informally used to designate naval autocannons or heavy railguns.

MACs are primarily divided into two distinct classifications; light MACs and heavy MACs (also referred to as Light Coil and Heavy Coil). Overall MAC generations are denoted as Marks, with specific models given a unique identifying code. Heavy MACs appear to be typically fitted on mainline fighting vessels such as those of the Autumn-class cruiser and Strident-class heavy frigate, while light MACs are predominantly fitted on lighter warships such as the Charon and Stalwart frigate classes, ships not intended as line warships such as the Epoch class carrier or ships historically considered under-gunned as capital ships, such as the Halcyon-class cruiser.

Some of the largest MAC types, such as those found on select orbital defense platforms and large warships, are referred to as "Super MACs".

Model	Mark	Size	Usage	Notes
14B11R2 battery		Light Coil	Halberd-class light destroyer	1x 1411BR2 battery; twin-linked 1170mm/647mm (46"/25.5") high-velocity coilguns. The larger gun is used for firing all standard munition packages, while the smaller is only used for firing kinetic rounds.
14D4A1	Mark V	Superheavy coil	Moncton-class orbital weapon platform	Can accelerate multi-ton rounds to "several kilometres per second".
	Mark V	Superheavy coil	Erőd-class orbital weapon platform	Capable of accelerating a 3,000 ton projectile to "point four-tenths" of lightspeed.
22B6R3 battery			Phoenix-class support ship (refit)	3x individual 530cm 22B6R3 MACs
20DA1C2			Gladius-class heavy corvette
20F989			Point Blank-class prowler
45J3D3	Mark IX	Heavy coil	Autumn-class heavy cruiser
49F9A1		Heavy coil	Marathon-class heavy cruiser
50GE1A		Heavy coil	Valiant-class super-heavy cruiser
56A2D4	Mark II	Light coil	Halcyon-class light cruiser Stalwart-class light frigate	In the case of the refit Halcyon-class cruiser UNSC Pillar of Autumn, the 56A2D4 runs two-thirds the length of the ship and employed special magnetic field recyclers along its length that, when combined with booster capacitors, allowed the gun to fire three times in rapid succession.
56A2F9	Mark II	Light coil	Epoch-class heavy carrier	Rapid-fire variant of the 52A6D4 model. On an Epoch, this weapon is intended as a defensive weapon though it was sometimes employed to add to coordinated volleys of fire.
5D7C2			Lancer-class fast-attack corvette	1x 5D7C2
5D8F6			Able-class heavy destroyer	The 5D8F6 was not standard on the original 2490 version and only became standard with the 2525 refit. Despite this, at least one Able, the UNSC Gorgon was refit with a MAC sometime in the 2490's
65P8V1		Light coil	Paris-class heavy frigate	1x 65P8V1 MAC
76G3V5 battery	Mark X	Superheavy coil	Vindication-class light battleship	1x 76G3V5 MAC battery; twin Mark X superheavy MACs
83B6R1			Hillsborough-class heavy destroyer
83B6R3	Mark II	Light coil	Charon-class light frigate	1x 83B6R3 MAC
90C1E1		Heavy coil	Orion-class assault carrier	2x 90C1E1 MACs
94B1E6	Mark IV	Heavy coil	Strident-class heavy frigate	Limited munitions supply, twelve capacitor banks for power.
CR-01D	Series 6	Superheavy coil	Punic-class supercarrier	2x CR-01D Series 6 MAC
CR-03	Series 8		Infinity-class supercarrier	Initial model also known as the CR03S8 MAC. Fielded on UNSC Infinity, these guns have a twenty-seven metre bore.
CR-03B	Series 8	Superheavy	Infinity-class supercarrier	Refit package model integrated late in 2558, though originally intended for the Eternity.

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  The 56A2D4 in the Pillar of Autumn.

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  The 56A2D4 in the In Amber Clad.

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  Internal workings of the 14D4A1 MAC on Cairo Station.

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  The forward CR-03B MAC's on the Infinity.

MAC batteries

"MAC batteries" refer to weapon systems in which multiple MACs are linked together as part of one weapon system. Such batteries may use differing bores and barrel lengths for different usage scenarios, or may consist of multiple identical guns.

Usage

Corvette MACs

Even on the smallest end of UNSC spacecraft designs, the MAC is a staple feature - forming the bulk of the spinal mount on the 243 metres (800 ft)-long Gladius-class corvette. The Gladius mounts a single 20DA1C2 MAC, and is currently the smallest known vessel to mount a full-scale ship MAC. The Lancer-class fast-attack corvette employs a single 5D7C2 MAC.

Frigate MACs

UNSC frigates typically run the length of the entire ship, averaging a length of 183 metres (600 ft). Frigates in the Human-Covenant War typically employed light MACs. The Stalwart and Charon-classes equipped a 56A2D4 Light Coil MAC and an 83B6R3 Light Coil MAC, respectively, with the post-war Strident heavy frigate equipped with a Mark IV 94B1E6 heavy coil MAC. Despite being a heavy frigate, the Paris-class employed a light MAC.

On the Paris and Charon-classes of ship, the barrel of the gun itself is located in the upper boom at the fore of the ship, with the lower boom containing fire-control systems and pulsed power storage. This is inverted on the Stalwart class, where the barrel is in the lower boom. The heavy MAC employed by the Strident frigate employs twelve capacitor cells, allowing it to achieve firepower levels similar to those of destroyers or light cruisers - limited only by the stock of ammunition carried aboard ship.

Destroyer MACs

The heavy destroyer UNSC Gorgon was the first ship of its class to mount a MAC, sporting one gun and carrying only three slugs. The later Halberd-class was fitted with a 14B11R2 MAC battery consisting of dual twin-linked 1170mm/647mm MACs, with the smaller gun only used for launching kinetic kill rounds and the larger gun compatible with all standard mission packages. The Halberd is able to fire its MACs on lower-than 100% charge levels for more rapid-firing, and can be equipped with MAC capacitor cells to easily recharge; these cells are easily replacable when damaged.

Destroyers like the Halberd are typically organised into wolf-packs, aiming to coordinate MAC volleys on enemy ships and overwhelm their defenses.

Cruiser MACs

Unlike their smaller counterparts, cruisers typically employ Heavy MACs as a standard armament - befitting of their status as the primary line warship of the UNSC Navy. The Marathon-class heavy cruiser sports two heavy MACs Late-war Marathons were in such high demand that even half-completed hulls were pressed into service for the use of their heavy MAC systems, often paired together with another Marathon as part of the "Gorgon" formation. These cruisers would pinpoint larger Covenant warships with sustained fire, giving smaller craft a chance to deal damage of their own.The Autumn-class heavy cruiser was fitted with a Mark IX heavy coil 45J3D3 MAC, and the Valiant-class super-heavy cruiser a heavy MAC of its own.

Contrary to the aforementioned examples, the Halcyon-class light cruiser does not employ a heavy MAC, but rather a light one - likely the cause of the ship being infamous for being undergunned within the UNSC fleet. When refit for Operation: RED FLAG, the Pillar of Autumn was fitted with a specialised modification to a Mark II light coil 56A2D4 MAC - the same as that found on the Stalwart-class light frigate. This gun ran two-thirds the length of the Autumn's length, and employed special magnetic field recyclers that - when combined with booster capacitors - allowed the gun to fire three times in rapid succession.

Carrier MACs

UNSC carriers employ a range of MAC types. On the smaller end, the Epoch-class employs the Mark II 52A6F9 light coil MAC, a rapid-fire upgrade of that seen on the Stalwart-class Frigate and intended for defensive purposes. In larger fleets, the Epoch may lend this MAC's fire to coordinated volleys. The Orion-class assault carrier employs a larger heavy MAC, while the extremely large Punic-class supercarrier employs two "Super-MACs", running the length of its enormous spaceframe. In addition to this, the Punic sports a number of smaller "Mini-MAC" turrets allowing it to fire on all angles.

Orbital defense platform MACs

Given their stationary nature, orbital defense platforms are able to employ much larger MACs than those employed on most warships, often dubbed "Super" MACs. The Moncton-class orbital weapon platform employed over Earth employed a single Mark V 14D4A1 MAC, purportedly capable of "putting a round clean through a Covenant capital ship". The 14D4A1 MAC employed on stations like Cairo Station employs hundreds of ALIM motors to line the barrel, capable of accelerating a projectile at multiple kilometres per-second. These stations employ stacked liquid-metal capacitor cells, allowing the gun to rapidly-cycle as long as their charge lasts.

The fortress-world Reach sported its own orbital defense guns, equipped with some of the most powerful MACs ever built. These rapid-firing MACs were connected to ground-based generators which allowed them to rapidly recharge and fire.

"Mini"-MACs

The so-called "Mini"-MAC is a nickname given to the primary weapon system employed by the ground-based M510 Mammoth siegework platform. The Mammoth sports a Mark 2457/35 cm HRG, a large railgun intended to target and eliminate hostile vessels, vehicles, and fortifications in terrestrial or suborbital positions. These weapons can be linked to a target locator, and are powerful enough to take out even Forerunner Z-8060 particle cannons.

A number of Mini MAC turrets serve as secondary armaments on the Punic-class supercarrier.

"Onagers"

An Onager MAC on Reach in the Asźod ship breaking yards.

Main articles: Mark 2488 Magnetic Accelerator Cannon, Mark 2551 Magnetic Accelerator Cannon

The Mark 2488 Magnetic Accelerator Cannon, informally known as the Onager, is a relatively small Magnetic Accelerator Cannon used for static defense. A manned version was used to defend the Pillar of Autumn on Reach. The Mark 2488 fires a 15 cm round with up to 1.1 gigajoules (0.25 tons) of kinetic energy. It is 32.6 meters long,

Related technologies

M68 Gauss Cannon

Main article: M68 Gauss Cannon

The M68 Gauss Cannon is a weapon mounted on the M12G1 Light Anti-Armor Vehicle as well as on stationary turrets. It utilizes the same coilgun technology used in MAC, but on a smaller scale.

M92 Principle Gauss Cannon

Main article: M92 Principle Gauss Cannon

The M92 Principle Gauss Cannon is a weapon system of similar MAC mechanics that runs along the length of the Open Frame 92/Extra-Vehicular Activity.

M99 Stanchion Gauss Rifle

Main article: Model 99 Special Application Scoped Rifle

The M99 is a man portable anti-matériel and anti-personnel special application weapon using 5.4mm/.21 caliber rounds. Like the M68 Gauss Cannon, it utilizes the same coilgun technology as a MAC, only on an even smaller scale. Though smaller than conventional ammunition, these rounds are accelerated to speeds fast enough to travel long distances with almost no change in trajectory, punch through any obstructing materials, hit their target, and still retain significant kinetic energy.

Mass drivers

Main article: Mass driver

The mass driver is an orbital launch assembly designed to propel low-weight payloads into orbit, otherwise known as orbital lifting, or to deliver them across a planetary system. The operating principle of the mass driver is essentially the same as that of the Magnetic Accelerator Cannon: it is a large coilgun that magnetically accelerates a package consisting of a magnetizable holder containing a payload.

While not a purpose-built weapon like the Magnetic Accelerator Cannon, these platforms are still potent weapons of opportunity. While never formally incorporated as a weapon, mass drivers have been used at as defensive magnetic accelerator weapons at Harvest, the Rubble, and Reach.

Gameplay

The MAC Blast in use.

Halo Wars

"Use the Spirit of Fire's awesome Mass Accelerator Cannon to incinerate enemy troops."

— In-game description.

In Halo Wars, the MAC Blast ability allows the player to use the UNSC Spirit of Fire's point-defense MACs for pinpoint orbital bombardment. It is mainly used as a support weapon to help the UNSC penetrate heavy Covenant defenses and Covenant bases, and is a potent weapon against Scarabs.

In Skirmish and multiplayer, the MAC Blast can only be used if Captain James Cutter is selected as the player's leader character. In the campaign, the MAC Blast is available in several missions, most notably Dome of Light, during which the player is granted access to forty rapid-fire MAC rounds to destroy a Covenant base that was located under a Covenant energy shield dome until part of the dome was overloaded using Rhinos.

Halo Wars 2

In Halo Wars 2, the MAC Blast has been upgraded by Ellen Anders and Isabel into MAC Blast EMP, which is very effective against all mechanical units. The EMP MAC is only available during the campaign mission "The Cartographer", where it is used to fire on a swarm of Aggressor Sentinels defending a Forerunner conduit. In Multiplayer and Blitz Mode, the MAC Blast is exclusive to Isabel and Sergeant Johnson. Isabel uses standard MAC rounds, while Johnson uses EMP rounds.

Changes from Halo Wars to Halo Wars 2

• MAC rounds can no longer can be upgraded via the Armory.
• Leader Points now can be used to upgrade MAC damage.

Gallery

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  An orbital defense platform above Reach firing its main cannon.

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  Nassau Station firing its MAC.

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  An example of an orbital defense platform firing its main cannon.

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  Cairo Station firing its "Super" MAC.

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  A frontal view of a Charon-class light frigate's MAC.

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  A closer view of the MAC muzzle on a Charon-class frigate.

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  Closeup side view of the MAC barrel on a Charon-class light frigate.

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  MAC slugs impacting the Forerunner Dreadnought, to little effect.

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  The UNSC Grafton firing its MAC at Spire One.

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  The muzzle of the UNSC Pillar of Autumn's MAC.

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  The UNSC Infinity fires her forward MACs at the Mantle's Approach.

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  The effect of a MAC round fired from an orbital defense platform on an Ceudar-pattern heavy corvette.

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  A MAC round impacting the surface of Harvest.

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  UNSC Commonwealth firing her MAC.

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  An Anlace-class frigate, lacking the traditional spiral mount, instead sports a downsized variant of the MAC atop its hull.

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  The rear of a slug for Cairo Station's Magnetic Accelerator cannon, seen in Halo 2: Anniversary.

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  The tip of a slug for Cairo Station's Magnetic Accelerator cannon.

List of appearances

• Halo: The Fall of Reach (First appearance)
• Halo: Combat Evolved
• Halo: The Flood
• Halo: First Strike
• Halo 2
• Halo: Ghosts of Onyx
• Halo: Uprising
• Halo 3
• Halo: Contact Harvest
• Halo: The Cole Protocol
• Halo Legends
  • Origins
• Halo: Evolutions - Essential Tales of the Halo Universe
  • Dirt
  • The Impossible Life and the Possible Death of Preston J. Cole
• Halo: Reach
• Halo: Combat Evolved Anniversary
• Halo: The Thursday War
• Halo 4
  • Spartan Ops
• Halo: Escalation
• Halo 2: Anniversary
• Halo: Fleet Battles
• Halo: The Fall of Reach - The Animated Series
• Halo 5: Guardians
• Halo: Shadow of Intent (Mentioned only)
• Halo Mythos
• Halo: Smoke and Shadow (Mentioned only)
• Halo Wars 2
• Halo: Envoy (Mentioned only)
• Halo: Silent Storm
• Halo: Oblivion
• Halo: Shadows of Reach
• Halo: Divine Wind
• Halo: The Rubicon Protocol (Mentioned only)