Weapon/Anti-Ship Model 21 Directed Ion Cannon

"It had us cold. The Assault Carrier swung right around the Zeus and was coming on our flank, our MAC turret wouldn't dent its shields. Then, the UNSC Thunder Lord fired off both its Ion Cannons, took that bastard's shields off straight away. It fired one of them again, blew out its wing section, screwed it with EMP. We blasted our MAC turret right into it's nose plasma turret and it just about blew off the whole entire prow section."

- Lieutenant Leonard Iridan

The is a experimental UNSC energy weapon, being mounted on warships. The weapon fires a particle beam of ionised atoms.

Description
The weapon ionizes hydrogen gas by either stripping an electron off of each hydrogen atom, or by allowing each hydrogen atom to capture an extra electron. When hydrogen gains electrons it forms anions. The weapon accelerates anions uses a traveling wave type particle accelerator. In this kind of ion accelerator, the negative ions are released inside a cylindrical ion acceleration chamber. This chamber has an electrode with an alternating electric charge of up to 1,000,000,000 (109) volts inside it. While the charge on the electrode is positive, the ions are attracted to the negative charge on the electrode, and thus bunched around it. The alternating voltage switches the charge to negative on the accelerating electrode. The negative charge electrostatically repels the negative ions and accelerates them to near the velocity of light. The resulting high energy beam of anions passes through a chamber filled with low pressure gas. There, collisions with the gas strip the extra electrons from the anions, and thus make the particle beam neutral. The particle beam proceeds straight to its target, and damages it by running into it, and by disrupting the structure of the target with its kinetic energy. The weapon has the background effect of Electromagnetic Radiation.

The weapon was in experimental stages during the Remnant War, being mounted on a limited number on Heimdall-class Frigates, Baal-class Destroyers, the larger, 21B version, mounted Thor-class Cruisers and the larger still C version being mounted on Ares-class Battlecruisers. During the Necros War it was brough out of experimental stages and mounted in increasing numbers, though no where near the same as the MAC and its varieties. The weapon was placed in lieu of MACs and had a augmentive effect when used in conjunction with MACs. The weapon was highly effective against ship shielding and its background EMP pulse could leave unshielded ships dead in the water.