A railgun is a device that uses electromagnetic repulsion to accelerate a projectile. Currently the United States military is looking into the use of railguns as naval weapons, although it will be some time before the first railguns are mounted aboard US navy ships. Railguns can achieve higher muzzle velocities than chemically-propelled firearms.
A similar kind of weapon is a coilgun, which uses magnetic coils instead of rails to accelerate a projectile. Arcflash Labs makes coilguns comparable in size to an infantry rifle or carbine, but these have such low accuracy and muzzle velocity that they are not really useful as weapons... yet.
Einhander is notable for being an avid fan of this technology.
Railguns in Science Fiction
Railguns are common weapons in science fiction; a few notable examples follow...
- In the Stargate universe, rapid-fire railguns are used by the United States as point defense weapons starting some time before the second season of Stargate Atlantis; they are used both as ship-mounted weapons and as towed AA emplacements (distingishable by blue tracers). The ones on Atlantis have 10,000 rounds and impact velocity of Mach 5 at a range of 250 miles.
- In the Warhammer 40,000 universe, the forces of the Tau Empire make use of railguns both in their navy and ground forces, with vehicle-mounted weapons on Hammerhead gunships, in their infantry as sniper rifles, and as shoulder-mounted heavy weapons on Broadside battle-suits.
- In the Halo universe, the UNSC uses large coilguns, called "magnetic accelerator cannons," as their primary anti-ship weapon, as well as using smaller Gauss cannons on some ground vehicles.
- Transformers: Revenge of the Fallen includes a rather gratuitous scene involving a US Navy railgun mounted on a cruiser.
- Most races in Mass Effect use "mass accelerators" that are similar to railguns as primary ship-to-ship weapons and firearms.