US Navy achieves '100 mile' hypersonic railgun test shot

Electro-hypercannon could bring back the dreadnought era

The US Navy, continuing its quest for a hypervelocity cannon which might restore the big-gun dreadnought to its lost dominion over the seas, has carried out a new and record-breaking railgun test.

This latest trial firing pushed muzzle energy to a blistering 33 megajoules (MJ). The muzzle velocity, as in the previous 10 MJ test in 2008, was still approximately Mach 7.5, but the heavier projectile used this time carried much more kinetic energy: approximately enough to strike targets 100 miles away in an operational weapon, according to the Office of Naval Research (ONR). The ONR wants to achieve lab trials at 64 MJ, potentially offering 200 mile range with projectiles striking at Mach 5, before trying to build an actual weapon.

A railgun works by passing vast amounts of electricity from one rail to the other via an armature linking the two: this generates a huge force driving the armature down the rails and out of the end of the gun. The armature can be the projectile itself, attached to it, or may be a sabot which will drop away once the slug is flying free.

The technical challenges of building railguns are many. Not least among these is the generation of very brief pulses of extremely high electrical power (the armature's run along the rails, even if they are quite long, is necessarily over very quickly – so the gun hasn't got long to put poke behind it). Then there's the matter of making rails that won't be destroyed by the armature screaming along them, which is yet to be properly sorted out (at the moment, the ONR only trusts its railguns to survive two or three shots before being knackered).

Assuming that the various issues of building a railgun can be solved, one must then deploy it to war and find power for it. About the only mobile platform able to supply the vast amounts of 'leccy required for a combat railgun is a warship, so it's no surprise to find the navy rather than the air force or army looking into this.

Not only would a 64 MJ railgun permit a warship to pound targets far away below the horizon with unstoppable Mach 5 hypersonic hammerblows, lesser hypersonic cannon might also sweep the skies of pesky, merely-supersonic aircraft and missiles.

Ever since the Battle of Midway, sailors have reluctantly been forced to accept that it is aircraft (and nowadays missiles) which win battles at sea, not ships: generally speaking it is also aircraft which permit navies to directly influence events ashore. The aircraft carrier long ago supplanted the mighty big-gun battleship as top naval dog.

But railgun warships might put an end to this, swatting down shipkiller missiles or attacking aircraft from afar with ease and splattering targets ashore quickly and responsively – no need to keep aircraft on station or wait endless tens of minutes for a subsonic cruise missile to cover the distance. The only way to deal with a railgun dreadnought – just as in the days of old when the first armoured all-big-gun battlewagons appeared – would be by using a ship just like it. Surface warships and surface-fleet officers, once again, would rule the seas and the naval roost.

Apart from all that, another major advantage would be on offer for navy logistics. Rather than troublesome missiles or shells crammed with explosive warheads and propellants, the supply chain would only need to handle inert projectiles and some extra supplies of fuel for the ships' engines. Railgun warships would be less prone to blowing up when hit in combat, too.

So it's all good, from a naval point of view. But the ONR has many hills to climb yet before their new technology is an actual functioning weapon rather than a one-off laboratory test rig. ®

Bootnote

The new Royal Navy Type 45 destroyers, the first warship class to use electric transmission for main full-speed propulsion, can supply a bit more than 40 megawatts of 'leccy. If fitted with one of the US ONR's desired 64-MJ railguns, they could recharge it for another shot in a little over a second and a half, though this rate of firing would leave little juice left for propulsion.

At the other end of the spectrum, a US Navy Nimitz-class supercarrier has twin 550-megawatt nuclear reactors (though it doesn't use electric transmission and so can't deliver this in the form of 'leccy). A railgun dreadnought built to the same outrageous scale would be able to ripple off 15 irresistible Mach-7 thunderbolts every second and still maintain steerage way.

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