The Buzz

US Navy's Railgun Dream Could Be Denied By Two Big Problems

There’s renewed interest of late in the US Navy’s (USN)  electromagnetic railgun. Plans to perform at-sea weapon testing appear to have been delayed in favor of further research. So, while development will probably continue, there are still two major problems holding the railgun back. The first is meeting the weapon’s massive power requirements at sea. The second is demonstrating that it’ll be ‘better’ than existing weapons.

The railgun launches rounds using electromagnetic force rather than explosive propellant. The USN prototype has 100MJ of pulse-power capacitors and a 25MW powerplant for recharging. The capacitors release their stored charge into the railgun barrel in a hundredth of a second, accelerating the projectile to about Mach 6. The USN’s goal is to fire ten rounds per minute, so the capacitors need to be recharged to fire every 6 seconds.

Few warships have the spare electrical capacity the weapon requires. The strongest candidate is the USN’s Zumwalt-class destroyer, whose 78MW integrated power system can dynamically distribute power between propulsion and on-board systems. It should have about 58MW of reserve power while steaming at 20 knots. By comparison, the Arleigh Burke-class destroyer has only 7.5MW for on-board systems.

The USN previously had several nuclear-powered cruisers, but the last were decommissioned in the 1990s. A new class of nuclear-powered warships could host multiple railguns (or other power-hungry weapons). But before the USN commits the kind of money required, it has to prove that the weapon is worth the investment.

There are three main roles envisaged for the railgun. The first is naval surface fire support—essentially artillery support for land operations. The Zumwalt’s 155mm Advanced Gun System (AGS) is also optimised for this role, using the rocket-assisted long-range land attack projectile (LRLAP).

The LRLAP is almost ten times the cost of a railgun hypervelocity projectile (HVP), but doesn’t match the railgun’s expected range. The HVP can also be made compatible with both the AGS and the 5-inch guns on USN’s cruisers and destroyers. Table 1 shows the estimated outcomes of this effort, although it doesn’t take into account the terminal effect of the munitions.

The HVP is a 10kg kinetic energy round, which means that the damage it does depends on its impact speed. A Tomahawk land-attack cruise missile packs a 450kg high explosive warhead, has a range in excess of 1,500km and costs about US$1.1m apiece. The USN has plenty of Tomahawks and efforts are underway to make them anti-ship capable. As well, the USN’s new-generation anti-ship cruise missile (LRASM) is stealthier than a Tomahawk, has a ship-penetrating warhead, and still has a range in excess of 900km.

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