The primary offensive armament of all UNSC capital ships is the Magnetic Accelerator Cannon (MAC). These weapons are massive coil guns that are used to accelerate projectiles ranging in mass from 600 tons in the case of smaller warships, and 3,000 tons in the case of Super MAC platforms, to extremely high velocities. These projectiles are composed of Titanium-A, depleted Uranium, and/or Tungsten with a ferrous (iron) core. Super MAC platforms accelerate MAC rounds to over point four-tenths of the speed of light or about 120,000 kilometers per second with twenty-three linear accelerator coils, while ship-based MACs have a lower velocity. Super MAC platforms can also reload a round in 5 seconds, where as the smaller capital ships will need several minutes .
The UNSC frigate Gettysburg is quoted as firing a 600 ton shell at 30 kilometers per second. Before Reach fell, the Pillar of Autumn was equipped with a modified MAC that could quickly fire three lighter projectiles in succession instead of just one heavier projectile. It was originally intended to allow the Pillar of Autumn a better chance of disabling a Covenant ship, which was a feature required for a mission that was later scrubbed following the Battle of Reach.
Almost all UNSC warships are equipped with Archer Missile pods for ship-to-ship engagements, which prove mostly effective against unshielded targets. A common tactic among UNSC ships is to disable the target's shields with MAC rounds and then pummel it with Archer missiles. UNSC ships in 2525 carried Fusion rockets as an offensive weapon. They seem to have been removed or replaced in later years. UNSC ships may also carry Shiva-class Nuclear Missiles. In addition, the UNSC mounts 50mm auto-cannons on its ships for defense against enemy fighters and boarding craft, controlled by shipboard AIs. However, these auto cannons can be used against Covenant capital ships if the two ships are close enough, as displayed by the UNSC Savannah during Operation Uppercut.
UNSC warships also carry significant Marine detachments for internal security, boarding actions, and planetary assault, and carry all the equipment and materiel needed by Marine forces. It is implied that a significant portion of the interior of UNSC warships are devoted to this purpose, as there are armories and barracks that hold these supplies.
Ships of the UNSC navy also carry a number of GA-TL1 Longsword-class Interceptor. These are armed with 110mm Rotary Cannons and ASGM-10 Missiles, and sometimes a Moray space mine system or even a single Shiva-class Nuclear Missile. They can also be remotely-operated and used to carry a remotely-detonated Shiva missile, which, when detonated, effectively destroys both the Longsword and its selected target.
Despite all of this firepower, however, UNSC warships have great difficulty defeating Covenant ships even with a numerical advantage. It typically takes multiple hits from a ship-based MAC weapon to disable a Covenant ship's shields, although larger, ODP-based Super MACs can fire a round that can literally shatter Covenant capital ships. Archer missiles must be used in tremendous amounts to breach Covenant shield systems. Even with their shields down, Covenant ships have been noted to remain operational after multiple direct hits from normal MAC rounds. This advantage in firepower and shielding gives the Covenant an effective 3:1 ratio and better against UNSC ships in combat.
