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"Enough of this. Bring up the railguns, let's finish this and go home."
— Theresa Yao

A railgun is a powerful ship-to-ship weapon used by the United Nations Navy (UNN), the Martian Congressional Republic Navy (MCRN), the Outer Planets Alliance (OPA), and Protogen Corporation for space combat.



Railgun Projectiles in The Expanse

Railguns are large, powerful mass drivers, cannons that use electroconductive rails and the Lorentz Effect to accelerate a dense metal slug at high velocities, relying on kinetic energy to punch clean through ships rather than warheads like with missiles. These weapons require significant power (presumably supplied by a fusion power-plant) to fire and must charge briefly before firing. They range from light, fast firing railguns with small calibers (presumably around 40 millimeters) to ultra-heavy types, firing much heavier slugs on a lower rate of fire.

Railguns are often spinal-fixed weapons (on ships smaller than battleships and cruisers) that require the ship to turn and face the target to aim the weapon. This is the case with Protogen's Amun-Ra-class stealth frigate[1], the Rocinante after her upgrade. Larger ships, however, can carry turreted railguns. The MCRN's Donnager-class battleships[2], the UNN's Leonidas-class[3] and Truman-class dreadnoughts[4] carry pairs of railgun turrets, allowing them to more easily engage targets without having to rotate the ship.

Railgun shots are powerful and accurate high-energy kinetic penetrators, capable of shooting clean through even large ships and doing critical damage, depending on their caliber and point of impact. Ultra-heavy/heavy railguns, mounted on battleships, are able of obliterating ships with a single hit, as shown by the MCRN Donnager against an Amun-Ra stealth frigate during the Attack on the Donnager. Smaller railguns are also capable of crippling bigger ships, if enough and accurate shots are acquired, and inflict severe damage on smaller units, taking them out with few well placed slugs. However in those cases, if the round does not strike any critical components, it will simply perforate the ship being attacked, leaving small holes that can be plugged relatively easily.

Though powerful and with technically almost unlimited range in space because of Newton's first law, railguns are limited in their effective range against targets in motion. Because while the round is quite fast but unguided, it can be dodged comfortably at longer ranges, although large slower vessels like the OPA Behemoth are more vulnerable. As a result, the use of railguns requires a sure lock and high accuracy in order to prevent misfires. Railguns are therefore used almost exclusively in CQB (close quarter battles) because there is no way to evade them or misfire in this situation. Because of their short-range lethality, it was considered suicidal to attack spacecraft such as a Donnager-class battleship at close range.[5]

Against immobile or very slow-moving targets however, the effective range is almost unlimited and in this scenario, largest and most powerful railguns are very effective weapons, capable in destroying their target over a millions of kilometers distance. The UNN proved this, when 5 of their orbital railgun platforms destroyed all 5 of the MCRN stealth C ballistic missile platforms positioned against Earth, during the UN-MCR War.

"But here they were, firing the ship's big cannons, which meant that the range was sufficiently short that a nonguided weapon was viable. Hundreds or even dozens of kilometers, not thousands."
— -Leviathan Wakes-

Ships and Stations carrying railguns[]

RPG MCRN flag Martian Congressional Republic Navy[]

RPG UNlogo United Nations Navy[]

RPG OPA logo Outer Planets Alliance[]

Protogenlogofromspacedockvideo Protogen[]

LaconiaFlagE Alt2 Laconian Imperial Navy[]


  • Rocinante: 1✕ keel mounted railgun (not standard to ship's design, added by crew)

Slow zone[]

Martian Congressional Republic Martian Congressional Republic Navy[]

UN logo United Nations Navy[]

Belternavybadge Outer Planets Alliance[]

Protogenlogofromspacedockvideo Protogen[]


  • Rocinante: 1✕ keel mounted ultra light railgun (not standard to ship's design, added by crew)

Ring space[]


*Possible Spoilers Alert*

Railguns first enter the stage on the MCRN Donnager, a Martian battleship, during the Attack on the Donnager against an attacking squadron of Protogen stealth frigates, taking out the attackers with single hits. The "bandits" then revealed their own railguns, putting shots clean through even the larger Donnager's hull. One shot penetrated so far into the Donnager that it decapitated Shed Garvey on its way through.

At the Assault on Thoth Station, a Protogen stealth frigate, the Osiris, brought her integrated railgun to bear against Rocinante at point blank range, scoring a hit on the frigate's hull. The shot hit nothing vital, but drove the Corvette-class light frigate back into the cover of the station until Amos Burton could fix a thruster hampering the ship's agility.

The Rocinante later acquired a spinal-fixed railgun of her own to further enhance her combat capabilities.

The UNN has deployed numerous UNN railgun platforms in Earth's orbit to serve as planetary defense platforms or more uncommonly as first strike weapons. 5 of these were used to eliminate 5 MCRN stealth C ballistic missile platforms aimed at Earth from long range, although one missile did fire before its launcher's destruction and struck a major South American city.

Once Fred Johnson recovered and claimed the Nauvoo, he rechristened it the OPAS Behemoth and, as well as installing 170 PDCs (Point Defence Cannons) and six missile launchers to the hull, had six heavy railgun turrets mounted to the bow. The mounting of these guns made the Behemoth the Sol system's largest-ever weapons platform.

Known Models[]

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UN logo Dawson-Pattern Medium Railgun[]

A sub-standard fully turreted railgun incorporated on the Leonidas-class. Part of the UNN's failed attempt at upgrading the fleet, Dawson-pattern turrets cannot be articulated under thrust, forcing ships that are armed with them to fire while drifting or to have to come to a relative stop. Leonidas-class are equipped with 2 Dawson-Pattern medium railgun turrets mounted opposite of each on the port and starboard sides of the hull.

UN logo Farren-Pattern Heavy Railgun[]

One of the most powerful and accurate weapon systems available to the UNN, matched only by the most advanced MCRN railguns. They are fully turreted. Its rounds impact almost instantly on targets within 1000 km. The Truman-class dreadnought is armed with 2 turret-mounted high-yield Farren-Pattern railguns mounted opposite of each other on the dorsal and ventral hull.

Martian Congressional Republic V-14 'Stiletto' Light Railgun[]

V-14 Stiletto light rail-gun sciroccoclass

A render of the V-14 'Stiletto' Light Railgun.

The V-14 'Stiletto' is a light turreted railgun employed by the MCRN on its Scirocco-class assault cruisers. These are 32 meters long.

Martian Congressional Republic VX-12 'Foehammer' Ultra-Heavy Railgun[]

An entirely new turreted railgun design purpose-built for the Martian Congressional Republic Navy's Donnager-class battleships, the VX-12 Foehammer boasts the longest range and greatest firepower of any ship-mounted railgun ever constructed. The barrel alone being longer than an entire Corvette-class, two such weapons are mounted on MCRN Donnager-class battleships. Another two 'Foehammer' railguns could potentially be mounted on hardpoints on the dorsal and ventral hull in the future.

OPA logo Zakosetara-Series Heavy Railgun[]

Six railguns of this fully turreted type were attached to the bow of the OPAS Behemoth. Zakosetara-series railguns were extremely powerful, and it was feared that the recoil from these guns would buckle the entire hull of the onetime generation ship, as well as causing ship-wide power grid failures, due to the ship not being designed for combat.

Protogenlogofromspacedockvideo S-24 "Khopesh" Light Railgun[]


A S-24 "Kopesh" Railgun briefly after firing a round.

The first ever railguns to be mounted onto a frigate-type vessel, one of these weapons was integrally mounted onto each of the Protogen Corporation's experimental Amun-Ra-class stealth frigates. These are spinally mounted, requiring the ship to face its target head on to aim the weapon. However, this gave a comparatively small warship a massive amount of firepower.


These turreted railgun models were supplied to the Free Navy at Medina station by the Laconian Empire to be incorporated on the Ring station.[6] They are extra large, and have an extremely high fire rate, and fire their projectiles faster than any other railgun model in history at about between 30 and 50K km/s. These railguns are between 230 and 250 meters long.


  • A railgun uses the Lorentz Force, in which it will move perpendicularly, or at a right angle, with respect to the direction of the current path and magnetic field to accelerate a projectile. The effect is initiated when a pair of electrically charged rails is bridged with an electroconductive material such as tungsten.[7]
  • 21st century US Navy testing of railguns[8] employ tungsten projectiles. Should the weapons be deployed, they will use tungsten or depleted uranium projectiles.[9]
  • In the Expanse series, rail guns are sometimes referred to as Gauss guns. This is inaccurate, as "Gauss gun" is a term for coilguns, which use magnetic coils to propel the projectile instead of conductive rails. The name "Gauss" comes from Carl Friedrich Gauss, an 18th-century German mathematician, who formulated mathematical descriptions of the magnetic effect used by magnetic accelerators. His principals are applied to coilguns.
  • The names of these weapons come from a variety of sources.
    • Foehammer references Tolkien's "Lord of the Rings," being the literal interpretation of Gandalf's sword "Glamdring." It is also referencing Stephen King's "Eye of the Dragon" and the callsign of a UNSC pilot in the "Halo" science-fiction franchise.
    • A khopesh is an ancient Egyptian curved sword.
    • A stiletto is a short knife with a thin, tapering blade resembling the heel of a woman's formal shoe.


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