The Orbital Magnetic Accelerator Cannon Platform, or Orbital MAC gun, is a geosynchronous weapons platform that fires a 2.727*10^6 kilogram projectile at four-tenths of the speed of light.  With a barrel length of 1336 meters this means that the projectiles undergo an acceleration of 2.10225*10^12 meters per second per second and experiences a force of 5.733*10^18 Newtons.  This imparts 7.66 zettajoules of kinetic energy, enough to punch clean through a Covenant capital ship's shields and still have enough energy left over to shatter the hull.