"That MAC gun can put a round clean through a Covenant Capital Ship."
— Sergeant Johnson, talking to the Master Chief on board the Orbital Defense Platform Cairo
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, nicknamed "Super" MACs or the "big stick", of these 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.
Overview
The operation principle of a MAC is the same as that of a coilgun. 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.
Mounting
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.
Ammunition
A standard ship-based MAC fires slugs of either ferric Tungsten or depleted Uranium at around 30,000 meters per second.[2] 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 point four-tenths the speed of light, around 120,000 kilometers per second.
Aiming
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.
Firing
The firing process uses electromagnetism to fire a ferromagnetic-tungsten slug at high velocity. An extremely large amount of current is put through the first solenoid (coil of conducting wire) which 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, turns on, which attracts the now high velocity metal slug just like the first solenoid, and the process is carried on. By the time the slug is fired out the end of the barrel it has been accelerated to a speed of approximately 30,000 meters per second for a ship-based MAC and around 120,000 kilometers per second for a "Super" MAC. For ODP, a pair of thrusters on the bottom side of the station fire for a couple of seconds to counteract the acceleration 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.
Types
Standard Magnetic Accelerator Cannon
The standard ship-mounted MAC fires a 600-ton ferric-tungsten projectile with a depleted uranium core at 30,000 meters 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 1.17 teratons of energy per shot a single ship based MAC round can destroy any unshielded Covenant ship in one shot.
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 the standard MAC cannon 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 range and velocity of the projectile is greatly diminished.
An average UNSC frigate sports one MAC system, while a standard destroyer possess two. UNSC cruisers carry two and UNSC carriers carry an unknown number of these powerful projectile weapons.
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 cannon to be fired three times per full charge, unlike traditional shipborne MAC systems, which could only fire once per charge. The Pillar of Autumn also carried new lighter MAC rounds that had a less dense ferrous core, but a harder outer layer of tungsten carbide. This technology is only possessed by the Pillar of Autumn and is never seen in gameplay. Also, the Pillar of Autumn's MAC charges up faster than normal UNSC MAC cannons, most likely due to the Pillar of Autumn's advanced reactor(s).
