M66 light railgun

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The M66 light rail gun (M66 LRG) is an anti-vehicle weapon system mounted in pairs to the SP42 Cobra self-propelled artillery vehicle, in conjunction with the larger M98 light rail gun. The M66 is often mounted in pairs to prefabricated automated defensive turrets for use as a static defensive measure.

Overview
The M66 LRG is a powerful anti-armor weapon that fires 30mm high-density ferrous projectiles at ultra-high velocity. The velocity of these projectiles allows them to penetrate armor at extreme range and with superior penetration to the M512 90mm cannon used by the M808B Main Battle Tank. Though the weapon performs similarly to the M68 Gauss cannon, the M68 is a coilgun, which operates on different principles from those of a railgun.

When twin-mounted on the SP42 Cobra and on automated turrets, each weapon is fired alternatively, as the energy required to fire both railguns together is beyond what the platform is capable of producing. This alternating also improves the weapon's rather low rate of fire, maintaining more consistent power output.

Trivia
The Halo Wars official website initially identified the weapon as the M66 50mm Gauss cannon. After the game's release, references to the M66 Gauss cannon were removed from official material and the weapon was renamed the LRG rail gun. It was stated that the Cobra uses a pair of 16 megajoule LRG rail guns when in normal mode and a single 8 megajoule version when locked down. Halo: The Essential Visual Guide retconned the 16MJ version of the LRG rail gun into the M66 30mm light rail gun, while it retconned the 8MJ version into the M98 105mm light rail gun.

List of appearances

 * Halo Wars