The Magnetic Accelerator Cannon, or MAC, is the primary weapon mounted on UNSC combat ships. By accelerating a depleted uranium or tungsten slug to a fraction of the speed of light, the UNSC is able to physically punch through everything from energy shielding to Forerunner armor plating.
The MAC is the UNSC's primary weapon, mounted on almost every ship larger than fighters. It operates as the key strength in the UNSC's alpha-strike tactics, however it has a long cooldown. This weapon's Covenant counterpart is the weaker Plasma Torpedo.