So the Navy has built a working rail gun….

Science got one step closer to science fiction Thursday morning, when the Navy used an electromagnetic railgun to fire a 7-pound slug at seven times the speed of sound.

The record-breaking shot, witnessed by a roomful of VIPs via remote camera at the Naval Surface Warfare Center, also moved the armed forces further down the road to a faster, safer, lighter, cheaper form of firepower.

So what are they going to use if for?

The Navy’s ultimate goal is a ship-mounted weapon capable of firing missiles 200 nautical miles in a six-minute arc into outer space and back to land, guided by GPS.

This dwarfs the range of the Navy’s current workhorse gun, the 5- inch MK 45, which shoots about 13 nautical miles.

The railgun uses electricity to propel its missiles, so they carry no fuel. The damage is caused purely by the kinetic energy of the missiles’ descent, which is projected to reach Mach 5, so they carry no warheads.

This means the missiles are cheaper. They are also smaller and safer, making them easier to store aboard ships and allowing for more variety in a vessel’s design.

For the Marines the gun would support, there are further benefits.

A ship carrying a rail gun would be able to begin bombarding the shore much sooner, far beyond radar range. It also would be able to fire more quickly.

The gun has a projected accuracy of 5 meters, which would minimize risk to Marines on the ground as well as any collateral damage.

I am sure that this gun has some uses as a ground support weapon. But I think that navy is being willfully blind here. A rail gun will only be an incremental improvements on the navy’s ability to blast ground targets. But it could change naval warfare completely. Just how would you defend a carrier from a rail gun?

Cruise missiles you can shoot down. In theory you can also shoot down ballistic missiles. But how are you going to stop an accurate rail gun that can fire from outside of radar range from sinking your carrier?