"Technology is more than merely the means by which weapons are forged, my student, it is proof that we shall prevail. There is no challenge we cannot overcome, no wisdom we cannot master, no opposition we cannot defeat. One by one, the secrets of the galaxy will become ours, and all the worlds touched by the light of our star will know the joy of the Greater Good. Progress shall be ours, so long as we have the will to seek it."
- — Commander Puretide
A Rail Rifle is a Tau ballistic Rail Weapon that makes use of electromagnetically-induced linear acceleration to fire a projectile at hypersonic speeds. A potent weapon, the Rail Rifle makes use of the same technologies as the larger Railgun and Heavy Rail Rifle, albeit on a smaller scale so that it is infantry portable. Possessing an impressive long range and ability to deal great damage, its true strength lies in its armour penetration capabilities. The Rail Rifle's projectile is able to punch through even Terminator Armour with ease. As a dedicated elite infantry killer, enemy units that manage to survive a Rail Rifle fusillade are often pinned down temporarily afterwards, unable to do anything in the face of such deadly fire. The Rail Rifle also proves effective when used against light vehicles. Rail Rifles have only recently been authorised for issue to frontline Tau units, having just completed an extensive field-testing phase. As of the Third Sphere Expansion, Rail Rifles are only issued to Pathfinder scout teams to provide them with their own much-needed heavy weapons support.
A Rail Rifle uses a series of super-conductive electrodes to electromagnetically accelerate small, solid and conductive projectiles to hypersonic speeds. The resulting high levels of kinetic force imparted to the weapon's projectile then allows it to penetrate and kill the most heavily armoured of enemy infantry at long ranges. Because the projectile is capable of achieving a velocity of anywhere between six and ten times the speed of sound, it strikes its target with such force that it produces more damage than what would be produced by an explosive charge of the same size. Such is the speed of the projectile that those near its ballistic path will often find the breath sucked from their lungs.
The size of the weapon determines the size of its power source and thus the kinetic force imparted to the type of projectile used as ammunition. Rail Rifles fire single, solid projectiles, and because the actual projectiles fired are so small, large numbers can be carried by the weapon's operator at a time; usually up to a hundred rounds of trilium-tipped solid darts. However, the energy requirements of the weapon are too great to be met by its internal power cell, and additional cartridge cells provide limited surplus power, fulfilling a role that can be likened to a ballistic weapon's ammunition magazines. A Rail Rifle makes an iconic "whip-crack" sound when it fires, which is created when the Rail Rifle's round breaks the sound barrier.
The basic physical principle behind Rail Weapon technology is well known to the Adeptus Mechanicus, but the Imperium has never been able to utilise it due to the myriad of issues inherent in the operation of such weapons. The limitations of such technology include the staggering amount of power required to propel the projectile along the rail, and the dissipation of the heat generated by the process. The Rail Rifle manages these issues through the use of several pre-charged disposable capacitors which are replaced after every shot.
Even before the Tau Empire's First Sphere Expansion had drawn to a close, Earth Caste scientists turned their efforts to further refining Rail Weapon technology, the goal being to create a version compact and durable enough for use by a Fire Caste infantryman. Thus did the development of the Rail Rifle begin. Success was not immediately forthcoming. Early Rail Weapons required substantial shielding in order to avoid flooding their Hammerheads and Battlesuits with harmful levels of radiation. These shields were inevitably formed of super-dense metal alloys, and contributed greatly to the mass of the weapon. Even when the payload of the prototype Rail Rifle was reduced, allowing a comparable reduction in power requirements, the weapon was too heavy to be carried by fewer than three Fire Warriors, and was therefore relegated to seldom-used defensive emplacements.
Progress was slow for many standard years. The Earth Caste reduced the Rail Rifle’s bulk by increments, but never by enough to meet their stated objective. Nevertheless, their labours were not wasted, as many of these refinements were retro-fitted onto existing Hammerhead and Broadside Railguns. Even though the goal of a Shas’la-portable Rail Rifle was still some way off, Rail Weapon technology as a whole was becoming more compact, more accurate and cheaper to produce with every year that passed.
The breakthrough finally came in the Second Sphere Expansion, during the campaign known to the Imperium as the Damocles Gulf Crusade. Here, the Tau were faced with a better-equipped enemy than any they had fought before, and the resulting conflict spurred unprecedented advancement in all fields of Tau scientific endeavour. Amongst the developments was a new ceramic, named or’es’var – literally "mighty bulwark" in the Tau Lexicon. Originally conceived as an ablative hull material to counteract the devastating effects of the Imperium’s fleet-borne Nova Cannons, the material was soon discovered to have unparalleled radiation absorption across a wide spectrum -- and better than that, it was light, almost weightless. With the way forward finally revealed, the Earth Caste presented the Fire Caste with the first prototype Rail Rifles.
At this stage, the Rail Rifle was still undergoing field trials with specialist units, but it was hoped that the new weapon could be issued more widely and eventually mass-produced. The relatively slow rate of fire, the bulk of the weapon and the early, unstable targeting mechanism did not meet the expectations of the Ethereal and Fire Castes, and these early prototypes often displayed a dangerous malfunction where the immense power generated by the weapon could generate fatal feedback through the Rail Rifle's neural targeting system. Yet the Rail Rifle's ability to penetrate armour made it highly valuable to Tau forces despite the difficulties incurred in its development. Indeed, it was found in early testing against various armour types in the Tau arsenal that only the armour used in XV88 Broadside Battlesuits could offer any protection against its fire. The weapon was capable of penetrating even the hardened carapaces of the larger Tyranid bioforms. The impact of the Rail Rifle was also such that its target was frequently hurled bodily by the impact, and this effect, combined with the distinctive whine of its hypersonic slug, often had a demoralising impact upon the foe.
Further developments of the weapon and refinements in its design eventually removed the risk of dangerous neural feedback to the user, and the weapon was issued to frontline Pathfinder units for field testing. This stable variant of the Rail Rifle has since been improved upon throughout the Third Sphere Expansion until it has reached its current refined state. At the sacrifice of a small modicum of range, the Rail Rifle is now used on the move more easily and can be fired faster. Its projectile can penetrate all known forms of infantry armour and even poses a threat to lightly armoured vehicles.
Now, centuries after its first development, the Rail Rifle is a common sight in Pathfinder vanguard and reconnaissance teams, though it has not yet fully supplanted the Pulse Carbine. Indeed, current Fire Caste doctrine dictates that Rail Rifles never be fielded to the exclusion of all other weaponry. Even though the current models are considerably more reliable than the initial prototypes, they are still prone to occasional misfires or targeting system failures. These mishaps occur rarely-- perhaps once in ten thousand firings -- but until this minor quirk is rectified, the Fire Caste will consider the Rail Rifle an augmentation to Pathfinder Teams, rather than a mainstay weapon.
Whilst Rail Rifles officially remains exclusive to Pathfinder Teams, there are persistent rumours that more compact versions of the weapon are currently being trialled by Fire Warrior cadres on the Tau Empire’s eastern fringe. It is difficult to say whether there is any truth to these tales, though it is certainly the Earth Caste’s avowed intent to oversee further refinement to the weapon. Their next goal is to evolve the Rail Rifle to a point where its killing power is comparable with its larger, Broadside-mounted cousins.
Rail Rifle Mechanics
A Rail Rifle functions through the manipulation of electromagnetic force. An electromagnetically responsive projectile in an electrically conductive sheath is inserted between two conductive rails attached to a power source, making a complete circuit. As the current moves through the circuit, it generates an electromagnetic force that pushes outward, forcing the projectile down the rails. The further the projectile moves down the rail, the greater the current generated and the stronger the electromagnetic force becomes, causing the projectile to accelerate along the full length of the rails. This allows it to achieve a tremendous velocity by the time it passes the end of the rails and breaks the circuit. After this, another round can be readied as soon as enough charge can be built up to power the next shot.
To achieve the necessary charge to fire a shell at combat velocity typically requires a bulky array of capacitors attached to a powerful generator, which a Rail Rifle provides via disposable capacitor packs that augment the weapon's own internal power supply. While a Rail Rifle is conceptually simple, manufacturing and fielding one presents several engineering challenges, requiring highly conductive materials with strong resistance to thermal expansion, efficient cooling systems, very precise machining processes, and methods of quickly servicing and re-machining the rails in the field to keep their interior surfaces in pristine condition. Even minor wear can have a significantly deleterious effect upon the weapon's performance.
- Chapter Approved 2004, pg. 46
- Codex: Tau (3rd Edition), pg. 17
- Codex: Tau Empire (4th Edition), pg. 30
- Codex: Tau Empire (6th Edition), pp. 42, 66
- Imperial Armour Volume Three - The Taros Campaign, pp. 68, 175, 198, 208, 284
- Deathwatch: Mark of the Xenos (RPG), pg. 6
- Warhammer 40,000: Munitorum - Rail Rifles (Digital Edition)
- The Kauyon (Audiobook), by Andy Smillie