Rail gunU.S. Navy demonstrates 100-mile hypersonic rail gun test shot

Published 14 December 2010

The latest test by the U.S. Navy of a rail gun saw a trial firing which pushed muzzle energy to a blistering 33 megajoules (MJ); the Navy 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

Navy's rail gun during an earlier test // Source: engizmo.ru

The U.S. 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 rail gun 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.

Lewis Page writes that a rail gun 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 rail guns 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 has not got long to put poke behind it). Then there is the matter of making rails that would not be destroyed by the armature screaming along them, which is yet to be properly sorted out (at the moment, the ONR only trusts its rail guns to survive two or three shots before being knackered).

Assuming that the various issues of building a rail gun 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 electricity required for a combat rail gun is a warship, so it is no surprise to find the navy rather than the air force or army looking into this.

Page notes that not only would a 64 MJ railgun permit a warship to pound targets far away below the horizon with unstoppable Mach 5 hypersonic hammerblows, but lesser hypersonic cannon might also sweep the skies of 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: it is also aircraft which permit navies directly to influence events ashore. The aircraft carrier long ago supplanted the mighty big-gun battleship as top naval dog.

Rail gun warships might put an end to this, swatting down ship-killer missiles or attacking aircraft from afar with ease and hitting 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 rail gun dreadnought — just as in the days of old when the first armored 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.

Page writes 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. Rail gun warships would be less prone to blowing up when hit in combat, too.