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The Magnetic Accelerator Cannon, also known as Mass Accelerator Cannon, MAC Gun and MAC Cannon, is a large coilgun that serves as the primary offensive weapon for UNSC warships. Larger versions are used as orbital defense platforms. MAC guns are the only non-nuclear weapons in the UNSC arsenal capable of effectively reducing or destroying Covenant capital ships' energy shields. Smaller shipborne versions can take as many as three hits to overload a shield while an orbital platform can put a hole through any Covenant vessel even with fully charged shields. The Magnetic Accelerator Cannon should not be confused with the Railgun, despite their superficial similarities. An Onager-class cannon is capable of disabling a CCS-class battlecruiser, with its shielding down.
The operation principle of a MAC is that of a coilgun.[notes 1] The cannon fires a massive metal projectile using a linear system of magnetic fields coils down a long shaft, increasing the projectile's velocity until it carries an incredible amount of kinetic energy. The ship-based models use ferric, ferrous, or depleted uranium cores, while orbital platforms and station-based versions use ferric tungsten rounds.
The size of a Magnetic Accelerator Cannon is such that it is normally an integral component of a warship's structure. Some types of Defense Stations are literally built around the massive weapon for orbital defense.
A standard ship-based MAC fires slugs of either ferric Tungsten or depleted Uranium and approximately 9.1 meters long at around 30,000 meters per second. The high muzzle speed gives the 600-ton slug the kinetic energy and momentum necessary to damage a target and partially mitigates the unguided nature of the slug and its lack of maneuverability. Orbital Defense Platforms fire a 3,000-ton slug at four-hundredths, or 4% of, the speed of light, around 12,000 kilometers per second.
Magnetic Accelerator Cannons are built into the superstructure of a ship or weapons platform, requiring that it maneuver in order to aim the weapon. Shipboard versions generally require an AI to aim the cannon, as the projectiles are unguided and are extremely hard to aim by manual fire. Orbital platforms have dedicated targeting computers.
The firing process uses electromagnetism to fire a ferromagnetic-tungsten slug at high velocity. An extremely large current is put through the first Solenoid (coil of conducting wire). This creates a strong magnetic field which attracts the metal slug. As the slug passes into the solenoid, the solenoid is quickly turned off and the second solenoid, which is further up, is activated, this attracts the now high velocity metal slug just like the first solenoid. This process is repeated along the barrel of the cannon. By the time the slug is fired out the end of the barrel it has accelerated to a speed of approximately 30 kilometers per second for a ship-based MAC and around 12,000 kilometers per second for a "super" MAC.
For ODPs, a pair of thrusters on the bottom side of the station fire for a few seconds to counteract the inertia imparted to the station. It normally takes five seconds to recharge the capacitors as well as load the slug, which is why boarding craft are usually deployed to take the stations out.
Mark II "Standard MAC"
The standard ship-mounted Mk. II MAC fires a 600-ton ferric-tungsten projectile with a depleted uranium core at 30 kilometers per second The large amount of energy needed to fire the weapon is particularly onerous on a warship, and the extended recharge time is a significant factor in combat against Covenant warships as multiple MAC rounds are required to penetrate Covenant shields. At 2.7e14 Joules per shot (KE = .5 x 600,000 kg x 30 km/s x 30 km/s), it has a standard destructive output of 64.53 kilotons TNT-equivalent.
Shipborne MAC draw power from the ship's reactor and require a charge of the weapon's magnetic coils in order to be fired. According to Halo: the Fall of Reach it takes three shots from a standard MAC to effectively lower the shields of a Covenant ship and destroy it. The time it takes to bring the MAC's systems to full charge on a UNSC vessel is the deciding force in a conflict. Thus, while a vessel may not run out of ammunition for a long time (depending on the size/weight of the shots and the capacity of the ship), a captain or commander has to carefully analyze the situation of a battle and use his shots strategically. The weapon can be fired even when not at full charge, but the velocity of the projectile is greatly diminished.
UNSC frigates and Halcyon-class light cruisers sport one MAC, UNSC destroyers and Marathon-class heavy cruisers carry two, UNSC carriers carry an unknown complement, and UNSC Infinity carries 4 MACs, most likely the most ever sported on a UNSC ship.
Mark II "Modified MAC"
When the UNSC ship Pillar of Autumn was refitted for the war against the Covenant, it received the latest version of the ship-based MAC weaponry. Magnetic field recyclers coupled with booster capacitors allowed the light coil cannon to be fired three times per full charge, unlike traditional shipborne MAC systems, which could only fire once per charge. Pillar of Autumn also carried new lighter MAC rounds that had a less dense ferrous core, but a harder outer layer of tungsten carbide. Also, Pillar of Autumn's MAC charges up faster than normal UNSC MAC cannons, most likely due to Pillar of Autumn's advanced reactor(s). This technology is only possessed by the Pillar of Autumn and is never seen in gameplay.
Mark 2547 "Mini MAC"
This weapon is first seen on the UNSC Mammoth and fires a smaller round than the standard MAC gun. It uses the same technology as the standard-sized MAC, housed in a smaller frame for more power during siege operations. It is capable of hitting targets in orbit.
Mark V "Super MAC"
- Main article: Orbital Defense Platform
UNSC Orbital Defense Platforms typically mount larger and more powerful versions of the standard Magnetic Accelerator Cannon, nicknamed "super" MACs or "the big stick."
These cannons fire a 3000-ton ferric-tungsten round at 12,000 kilometers per second, or 4% of the speed of light, impacting with a massive amount of kinetic energy. According to the formula for kinetic energy, KE = 0.5 * m * v2, the force of each shot will be, 0.5 * 3'000'000 * 11991698.322, which is 2.15701e20. Given that a kiloton = 4184000000000 joules, then each shot produces 51553834.34 Kilotons of force (51553.83 Megatons, or 51.56 Gigatons)
Against Covenant shield technology, the rounds possess enough kinetic energy to punch through shields, cut through the ship, and, upon exit, still retain enough energy to destroy a second ship, and cripple a third ship.
It is theorized that if a ship's armor or shields were to absorb all the kinetic energy of a super MAC round, the release of thermodynamic energy would still vaporize the ship. By receiving power from ground-based power plants, orbital platforms could achieve recharge and reload times as short as five seconds.
Series-8 "Super-Heavy MAC"
Only seen on board UNSC Infinity, the CR-08 Series-8 MAC fires an ultra-dense projectile at a fraction of the speed of light and is capable of creating terrestrial craters several miles wide. The shock-wave generated is powerful enough to knock in-atmosphere star ships out of the air. Its exo-atmospheric combat capabilities were shown when the UNSC Infinity managed to use the Series-8 to puncture the Mantle's Approach's hull.
M68 Gauss Cannon
- Main article: M68 Gauss Cannon
The M68 Gauss Cannon is a UNSC weapon mounted on the M12G1 Light Anti-Armor Vehicle as well as on stationary turrets. It utilizes the same coilgun technology used in Magnetic Accelerator Cannons, but on a smaller scale.
M99 Stanchion Gauss Rifle
- Main article: Model 99 Special Application Scoped Rifle
The M99 is a man portable anti-material and anti-personnel special application weapon. Like the M68 Gauss Cannon, it utilizes the same coilgun technology as a MAC, only on an even smaller scale, using 5.4mm/.21 caliber rounds. 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.
M92 Principle Gauss Cannon
The M92 Principle Gauss Cannon is a Magnetic Accelerator Weapon that runs along the length of the Open Frame 92/Extra-Vehicular Activity.
- Main article: Mass driver
The mass driver is a somewhat primitive United Nations Space Command orbital launch assembly designed to propel low-weight payloads into orbit, otherwise known as orbital lifting. 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 UNSC's 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, Reach, Ivanoff Research Station and on UNSC Infinity.
- “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 UNSC Spirit of Fire's MAC 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 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, a feat that would be impossible outside of gameplay.
- The Magnetic Accelerator Cannon is twice wrongly addressed in the Halo Universe - once as the "Mass Accelerator Cannon" in Halo: Contact Harvest, and as the "Mass Accelerated Cannon" in Halo Wars.
- The upgraded colony ship UNSC Spirit of Fire's MAC cannon is unable to penetrate a Covenant citadel's shield in Halo Wars with one round.
- The total energy released from the impact of a MAC round fired from a UNSC Orbital Defense Platform releases a colossal 194.7 exajoules of energy (46.5 gigatons). To put this in perspective, this is about 3,090,195 times the energy released from the atomic bomb detonated over Hiroshima in World War II, which released a comparatively small 63 terajoules of energy (15.5 kilotons).
- According to calculation based on given statistics, a blast coming from a shipborne MAC has 58.16 kilotons of force. The given math is as follows. In order to find the kinetic energy of the round, you must take the velocity(30,000 m/s) and square it (900,000,000) then multiply that by the projectile weight (540,784 kg) and then divide that number by 2. This gives us 243 terajoules of energy approximately 2.5 times as powerful as the more powerful Fat Man atomic bomb dropped on Nagasaki in World War II.
- The primary MAC on UNSC Infinity was capable of creating a crater several miles wide on Sanghelios.
- ↑ A coilgun (not to be confused with a railgun) is a type of cannon which uses one or more electromagnetic coils to accelerate a magnetic projectile to high velocity.
- Halo.bungie.org: Overview of an Orbital Defense Platform by Stephen Loftus
- Wikipedia's article on Coilgun