What is a railgun?

A railgun is a military device that is designed to launch high-velocity projectiles. railguns usually achieve speeds of Mach 3 (about 3700 km/hr). However, recent research shows that potentially higher velocities of Mach 10 (at sea level) can be attained in the near future. As opposed to conventional firing methods (i.e. gunpowder), railguns instead utilize the electromagnetic field to achieve extremely high muzzle velocities. Not relying on chemical propellants means that the railgun can be more efficient and powerful. Although railguns are usually installed on warships, both the US and China have been researching ways to miniaturize them and transform them into hypersonic guns. 

Early concepts of railguns

Although railguns seem to be a relatively modern concept, the idea of one has actually existed as far back as the late 19th century. Railgun-like devices were frequently depicted in sci-fi novels. 

Nevertheless, the technology was soon going to be a reality. In 1917, at the height of WWI, French inventor André Louis Octave Fauchon-Villeplée designed a prototype. As the French military had to modernize during WWI, the French government was intrigued by Fauchon-Villeplée's contraption. Hence, one year later, he was tasked with designing a viable electromagnetic cannon in order to rival the Paris Gun. However, the project was scrapped by the French military because WWI came to an end that year.

During the interwar period (1918-1939), research and development pertaining to the railgun stagnated as the railgun required an excessive amount of energy to operate. In spite of these technical challenges, railgun innovation persisted in WWII. German engineer Joachim Hänsler, who worked in the Nazi Ordnance Office, conceptualised a railgun that could reach a starting velocity of approximately 2000 m/s (Mach 5.8). Later on, American researchers concluded that his prototype needed enough energy to illuminate half of Chicago, which meant that railguns still consumed significant amounts of energy.

Railguns in the modern era

In the 1950s, Mark Oliphant, an Australian physicist, worked on the world's biggest homopolar motor; this could be a candidate for the energy source of a railgun. During the next few decades, laboratories and research institutes across the United States, the United Kingdom, and Australia focused on this technology.

However, other countries have began proliferating railguns, one of them being China. Even though their development into this technology has been greatly exaggerated, it is still a cause for concern for Western countries. 

Other countries such as India, Russia, and Turkey have conducted research on railguns.

How does a railgun work?

As mentioned earlier, railgun projectiles are propelled via electromagnetism. The Lorentz Force, which acts on a charged particle that moves through an electromagnetic field*, is responsible for accelerating railgun projectiles to extremely high speeds. 

A railgun is essentially a massive circuit that is made of two conducting rails (usually made of copper or other low-resistivity materials) instead of wires. Apart from that, the railgun uses a projectile made of a solid conducting material (usually aluminium) that can travel down the rails.

Firstly, a voltage source is essential to generating a large current. This is usually accomplished through capacitors as they are able to discharge extremely quickly in the absence of circuital resistance. Alternative energy sources such as pulse generators, disc generators, and homopolar motors are used as well.

Next, the current running through the rails generates a magnetic field. As per the right-hand rule, the magnetic field circulates around the rails. As the currents in the rails are in opposite directions, the overall magnetic fields do not cancel out. The current needs to be in the order of a million amps if the railgun is to launch projectiles at high speeds.

Per the equations* F=ILB (note that the magnetic field and projectile are perpendicular) and B=μ0I/2πr, a large current in needed for a strong Lorentz Force. Since the value μ0 is very small, a large voltage source (such as the aformenetioned capacitors) is required to generate a strong magnetic field. Additionally, the rails need to be long enough so that the magnetic field is powerful enough; hence, attempts to miniaturize the technology have been unsuccessful.

The Pros of Railguns

One of the major advantages of railguns is its ability to fire projectiles at significantly greater speeds than conventional artillery; this means that naval warships can attack from far away. In fact, the range of railguns is about 10 times that of ordinary weapons. Due to the insane muzzle velocity of the railgun projectiles, they are not affected as much by the wind, so railguns have greater accuracy. Last but not least, the kinetic energy of these projectiles is comparable to that of a tomahawk missile!

Not only do railguns have military applications, they can also be a vital tool in space missions (this concept has existed as far back as 2010!). The tech itself has a lot of variations that are being explored, examples being the helical railgun and the plasma railgun.

The Cons of Railguns

However, railguns do have significant drawbacks. Not only do they require insane amounts of energy, they also suffer from resistive heating (aka Joule Heating), which is caused when an electric current passes through the conducting rails. This may cause the rails themselves to melt if there is sufficient heat. Most attempts to fix this problem have been unsuccessful for the time being. Finally, as the magnetic force between the rails is repulsive, it can possibly cause the gun to wear and tear.

Notes on the mathematics

In this article, embedded links were included to supplement the understanding of these equations. However, here is a slightly more in-depth analysis.

^The electromagnetic force is composed of an electric field E and a magnetic field B, usually described in terms of vector fields.

*F=Force (Newtons), I=Current (Amperes), B= Magnetic Field (Teslas), r=Distance from the wire (metres), μ0= Magnetic permeability (4π*10^-7 NA^-2 in a vacuum). The equation for the magnetic field assumes an infinite-length wire/conductor; as this approximation can be unrealistic as the conducting rails are treated as one-dimensional, a better equation is shown below. Both equations can be derived using the Biot-Savart Law (whereas the first equation can also be derived with Ampere's Law), albeit with different assumptions (however, both equations assume the rails are significantly larger than the projectile).

Variables for the equations below: B (magnetic field), d (distance between the centerpoints of the rails), r (Radius of the rails), s (distance from the rails).

Sources/further reading:

Although some links have been featured in the article, here is a more extensive resource list on railguns.

Suciu, Peter. “Railguns: Everything You Always Wanted to Know.” The National Interest, The Center for the National Interest, 4 Sept. 2020, nationalinterest.org/blog/buzz/railguns-everything-you-always-wanted-know-168479.

Exmundo, Jex. “Railguns: All You Need to Know about the Weapon That Uses Electromagnetic Force.” Interesting Engineering, Interesting Engineering, 3 Nov. 2022, interestingengineering.com/innovation/railgun.

“What Is a Rail Gun and How Does It Work?” Defensebridge, Defensebridge, 17 May 2023, www.defensebridge.com/article/what-is-a-rail-gun-and-how-does-it-work.html.