From Halopedia, the Halo wiki
A coilgun, also known as a Gauss gun, is a type of mass driver weaponry employed by the United Nations Space Command for both ground and space applications. Coilguns utilize electromagnetic coils to propel a hyperdense projectile to high speeds. Coilguns are similar in design and function to railgun weaponry as both make use of electromagnets in their operation.
Coilguns utilize a series of electromagnetically charged coils powered in a timed sequence to propel a magnetic projectile at speeds faster than that of chemical weaponry. UNSC coilguns almost exclusively utilize Asynchronous Linear-Induction Motor (ALIM) technology which is capable of accelerating a projectile to such speeds that its impact seems instantaneous from the point of firing.
Mass drivers are a form of typically stationary coilgun used to fire payloads at high velocities.
Magnetic Accelerator Cannons
Magnetic Accelerator Cannons are naval coilguns employed for ship-to-ship combat by the UNSC Navy.
M68 Gauss Cannon
A smaller, portable coilgun often mounted on the M12G1 Gauss Warthog or independently on a mount.
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