There wasn’t much left of the 23-pound bullet, just a scalded piece of squat metal. That’s what happens when an enormous electromagnetic gun sends its ammo rocketing 5,500 feet in a single second. 

The gun that fired the bullet is the Navy’s experimental railgun. The gun has no moving parts or propellants — just a king-sized burst of energy that sends a projectile flying. And today its parents at the Office of Naval Research sent 33 megajoules through it, setting a new world record and making it the most powerful railgun ever developed.

Reporters were invited to watch the test at the Dalghren Naval Surface Warfare Center. A tangle of two-inch thick coaxial cables hooked up to stacks of refrigerator-sized capacitors took five minutes to power juice into a gun the size of a schoolbus built in a warehouse. With a 1.5-million-ampere spark of light and a boom audible in a room 50 feet away, the bullet left the gun at a speed of Mach 8.

All that energy was “dump[ed] in 10 milliseconds,” says Charles Garrett, project manager at Dahlgren for the railgun.


But since there no explosion powering the projectile, why should the railgun have made any noise at all? Answer: the bullet went so fast it released a sonic boom.

Since 2005, the Navy has spent $211 million testing whether it can harness electromagnetic energy into a gun. The ultimate goal is to fire the gun at 64 megajoules, making it capable of sending a bullet 200 miles in six minutes. That’s 10 times farther than the Navy’s already-powerful guns can fire, keeping its ships far out of range of enemy anti-ship systems.

The Navy wants to put the railgun on a ship and power it through the ship’s batteries, something that’ll take years to develop. And since the gun’s power can be adjusted — it depends only on the batteries and the capacitors on board a ship, railgun scientists explained — it could theoretically be used to stop cruise missiles or even ballistic missiles.

That’s still a long way off. The Office of Science and Technology will keep running tests until 2017, largely for “thermal management,” says program manager Roger Ellis, basically to ensure that the materials used for the gun don’t get as fried as the bullet under the intense power generated. The Navy guesstimates that it’ll be ready for shipboard defense between 2020 and 2025.

Oh, and the last record holder for most powerful railgun? The same gun when it fired off a shot using 10.64 megajoules two years ago.

By Spencer Ackerman December 10, 2010