Science fiction authors seem to love to imagine the weaponry of the future more than they do almost any other aspect of technology's ongoing march forward. When considering the combat systems that might codify World War IV or V, certain ideas seem to take hold and become popular go-to choices.
When a sci-fi fan imagines a standard weapon of the genre, they might picture the classic Star Trek phaser or the iconic Star Wars lightsaber. While lasers have a long and storied history, there are still some works that prefer good old-fashioned lead and steel. Those who are feeling indecisive, however, will be happy to know that there's a great option in-between.
Magnetic weapons use magnetic fields to accelerate a physical projectile or to focus a charged particle beam. Go-to examples include railguns, which use two parallel metal rails to produce a magnetic current between them, and coilguns, which pass the current along a single line and pulse in sequence to fire. In the real world, their military applications are limited and largely experimental. Modern research suggests that magnetic weapons can fire projectiles with much greater velocity than traditional explosive charges. This means that a weapon such as a railgun might have substantially greater range than a typical gun. Many logistical concerns render the weapon less ready for real-world military application, including the difficulty of acquiring and transporting an appropriate power supply. Researchers have been at work on this concept for ages, and there are tons of consumer-ready magnetic weapons, but they may never be ready for war. Wars of the sci-fi future, however, love the concept.
The first example of this trope in science fiction came in 1897, seven years before the first coilgun was patented. Norwegian scientist Kristian Birkeland claims to have been working on the concept from as early as 1845, but the concept wasn't publicly known until 1904. John Munro's novel A Trip to Venus tells the tale of a group of astronauts who discover the toxic planet to house a utopian society. This era was the wild west when it came to depictions of space travel since the real thing was such an outlandish idea. Anyone could reasonably suggest a way someone might make it past the atmosphere and any guess would be considered valid. Munro's novel suggested a system identical to what mankind now knows as a coilgun, but on a scale large enough to launch a spaceship. Munro's description is uncanny, and he also correctly guesses concepts like retrofired rockets and compressed gas jets. Whatever the merits of A Trip to Venus as a work of fiction, Munro had some incredible insight into the future of space travel.
One of the first uses of the concept as a weapon came in Robert A. Heinlein's groundbreaking 1966 novel The Moon is a Harsh Mistress. Heinlein is one of the fathers of science fiction as a modern discipline, so it stands to reason that he would put his fingerprint on this concept as well. The plot of The Moon is a Harsh Mistress concerns a violent uprising by the incarcerated denizens of the moon, which has been turned into an off-world penal colony. Heinlein describes a method of delivering grain to Earth from the farming land on the moon via a miles-long mass driver system. During a revolt, the citizens of the moon weaponize this mass driver system to fire steel-dipped stones as an orbital cannon. It's a devastating weapon concept that has its origins in real life and countless other authors have used similar ideas.
Amongst more modern science fiction, the magnetic weapon is simply one option of many that are available to the armies of the future. James S. A. Corey's beloved sci-fi novel series The Expanse takes a slightly harder sci-fi look at the humble railgun. In mid-range ship-to-ship combat engagements, the railgun is the ideal choice. If the ships are too far apart, the target can simply evade, but the steel projectiles can't be targeted by torpedoes. The lesser-known Arnold Schwarzenegger classic Eraser was built around the illegal smuggling of handheld railguns, which were pitched as weapons of mass destruction. Neil Blomkamp's second feature Elysium featured a ChemRail gun, which is pitched as a comically destructive arm-held weapon. Most modern sci-fi epics see the railgun as the end all be all, largely just because of how cool it looks.
Another interesting version of the trope largely comes from anime. Some characters pitched with superhuman powers can use their gifts to function as a railgun. The character most directly tied to the term is unquestionably Mikasa Mikoto from A Certain Magical Index. Mikasa uses her powers to electrify the air in two rails, firing a coin off at breakneck speed. This iconic moment is a ton of people's mental image of the term railgun. Kentaro Yabuki's early 2000s manga hit Black Cat features a similar concept. Lead character Train uses electrical powers to magnetize his revolver and wield it like a railgun. This is a more supernatural take on the trope, but it still fits well in its evolution.
Magnetic weaponry is a fascinating concept that evolved from the scientific exploration of the day into one of the coolest sci-fi ideas. It's a perfect example of how science informs science fiction.