They still guzzle way too much power.
The US Navy has been wowing people with electromagnetic railguns, a long-range electrically-powered weapon, in concept and prototype for years now. But the single big obstacle that keeps the railgun off boats remains the same as it ever was: ships can't generate enough power to fire them.
At the Naval Future Force Science and Technology Expo, Vice Adm. William Hilarides explained that three problems with the railgun remain: room on ships, integrating the new weapons with the old weapons systems, and power—as in, not enough of it.
The railgun doesn't rely on chemical explosions like more conventional weapons. Instead, the projectile is housed in a electrically conductive metal armature, which connects two parallel, 30-foot rails. A huge 25-megawatt electric pulse is sent down the rails, creating the magnetic fields that shoot the armature and projectile out.
For the Navy, the upsides to an electromagnetic railgun are clear: its range of 100 miles is about double that of conventional high-velocity projectiles, and its projectiles, which go seven times the speed of sound, aren't explosive.
Not only does this make them cheaper and easier to store and transport, but it also eliminates the threat of ordnances lying unexploded long after the war ends.
It takes a significant amount of power to fire something that far and fast, however.
It's hard to conceptualize 25 megawatts, for me anyway. For some perspective, the Navy's next generation Zumwalt-class destroyer, the 21st-century stealth battleship with electric engines, is powered by a 78-megawatt array of turbine generators. So, firing a rail gun once would take almost a third of the most advanced ship's whole capacity. Most ships today don't have more than 9 megawatts to spare, according to Popular Science.
For now the next generation ships are being designed with two 155mm Advanced Gun Systems, which are also all electric but fire conventional rockets and require 800kW of power—much less than the railgun but still more than most ships today can handle.
Hilarides said that, physics willing, one of those systems could be removed to make room for a railgun.
"We have begun real studies—as opposed to just a bunch of guys sitting around—real engineering studies are being done to make sure it's possible," he said. "It's physics. Without taking something off, you're not putting on a many ton system, so a gun would be a logical thing to take off and put the railgun in its place."
The railgun is going to be tested on the USNS Millinocket next year. The first of three Zumwalt-class ships—railgun or no railgun—is slated to be delivered to the Navy next year, and the last in 2018. They're estimated to cost $22 billion in total.