A Railgun is a heavy T'au ballistic Rail Weapon that makes use of electromagnetically-induced linear acceleration to fire a projectile at extraordinary speeds. Characteristically powerful, Railguns are renowned for their deadliness to enemy armour at extreme ranges. The cylindrical projectile it fires can hammer straight through Power Armour and even redoubtable Tactical Dreadnought Armour with ease, passing through at such incredible velocity that the sudden burst of pressure followed by violent decompression reduces all living matter inside to a tangle of semi-liquid mush. Even a Space Marine's enhanced physiology is no match for such pinpoint devastation.
The Railgun is roundly hated by the Adeptus Astartes Chapters that have encountered it, for not only does it kill their Battle-Brothers upon impact, but it destroys or renders inoperable the Progenoid Glands that allow their Apothecaries to create more Space Marines from the fallen. In this way, it not only kills the Adeptus Astartes of the present, but also kills the warriors of the future. The Railgun is most commonly mounted on the Hammerhead gunship and Swordfish gunship, though larger variants have been employed as starship weapons by the Kor'vattra (T'au Navy).
A Railgun uses a series of powerful electromagnets and super-conductive electrodes to accelerate small, solid and conductive projectiles to a significant fraction of the speed of light in a vacuum. The resulting high levels of kinetic force imparted to the weapon's projectile then allows it to devastate and destroy the most heavily armoured vehicles on impact, even at extremely long ranges. Few vehicles are able to withstand a direct hit from a Railgun without suffering critical damage. Because the projectile is capable of achieving a velocity of 0.02c (2% the speed of light), it generates a tremendous force when it strikes its target that is often far more than would be produced by an explosive charge of the same size. As such, the speed of the projectile is enough to punch through virtually any amount of armour. 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.
Railguns usually fire single, solid projectiles and rely on the projectile's speed to penetrate armour, even at long ranges. Because the projectiles are so small, large numbers can be carried by the weapon's operator at a time. However, when used against infantry, a Railgun can have a devastating effect where the round will simply vaporise the target. Those near the travelling path of the projectile will also find the breath sucked out of their lungs, such is its speed. A Railgun makes an iconic "whip-crack" sound when it fires, which is created when the Railgun's round breaks the sound barrier. A Railgun is also able to fire sophisticated submunition rounds, which consist of smaller projectiles that can strike a wide area. Whilst the overall damage imparted on impact is less, such submunitions are extremely useful for suppressive area fire against infantry targets.
The basic physical principle behind Railgun technology is well known to the Adeptus Mechanicus, but the Imperium has never been able to utilise it in a worthwhile form 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 T'au appear to have implemented solutions to these problems, and many Hereteks amongst the Adeptus Mechanicus would very much like to understand how.
Theorised Railgun Mechanics
The Railgun functions through the manipulation of the electromagnetic force. A magnetically 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 a magnetic force that pushes outward, forcing the projectile down the rails. The further the projectile goes out, the greater the current that goes through and the stronger the magnetic force becomes, causing the projectile to accelerate along the full length of the rails, achieving 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 back up for the next shot.
To achieve a charge necessary to fire a shell at combat velocity typically requires a bulky array of capacitors attached to a powerful generator, which tends to limit the use of the battlefield Railgun to dedicated vehicles. While a Railgun 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 as even minor wear could have a significantly deleterious affect on the weapon's performance.
A Heavy Railgun is a larger version of the standard Railgun and is usually only mounted on the Manta, Moray and Tiger Shark AX-1-0 aircraft. Heavy Railguns fire larger rounds at higher speeds, and the projectiles are fin-stabilised to provide extra lift, and therefore extra range, whilst in an atmosphere. The Heavy Railgun's submunition shell is equipped with a drone processor that is programmed to direct the shell accurately towards its target. This capability is mostly used during void combat to find weak points in the armour of enemy starships as standard submunition rounds lack the necessary penetrating power. They are also useful in ground combat, however, as the shell can saturate an extremely large area with its submunitions and deny cover more effectively to enemy forces due to being fired from the air.
Starship Railgun Batteries
Despite recent T'au advances in superconductor technology, Railguns mounted on T'au starships are of such enormous size and require such large amounts of energy to fire that they are grouped into batteries and fired one barrel at a time in sequential order, ensuring the first barrel is loaded and ready before it is charged again. T'au starship Railgun batteries are considered comparable in firepower and effectiveness to the weapons batteries of Macrocannons employed by Imperial starships.
- Battlefleet Gothic Armada (Specialty Game Background Book), pg. 98
- Codex: Tau (3rd Edition), pg. 17
- Codex: Tau Empire (4th Edition), pg. 30
- Codex: Tau Empire (6th Edition), pp. 50, 66
- Courage and Honour (Novel) by Graham McNeill
- Deathwatch: Mark of the Xenos (RPG), pg. 6
- Imperial Armour Volume Three - The Taros Campaign, pp. 68, 175, 198, 208, 284
- Warhammer 40,000: Dataslate - Tau Firebase Support Cadre (Digital Edition)