For me, watching a movie with less than accurate battle scenes or soldiers using pistols for 500-yard kill shots is a travesty. I find novels with a poorly written military and weapons used inaccurately impossible to read. I am not the only person that feels this way. Most readers will react the same way.
You need to understand several things before you can begin to develop an army much less write about that army. There are a lot of modern and ancient weapons to consider, but for this article assume any examples I use involve medieval arms, armor and tactics. It doesn’t matter what era your weapons or military comes from; what matters is accuracy and getting the details straight.
You need to know what a bow does and can do and the same goes for a sword or mace. Do the research so you know how leather armor reacts to a sword strike compared to a metal armor. A sharp sword with enough power behind it could slice through leather armor, but the same attack would only dent metal armor.
That said, special consideration is given to novels in which the protagonist is supposed to be superhuman or able to accurately hit targets with a bow at 100 yards. Sixty yards is considered a sniper shot with a bow here in the real world, but we are writing fiction. If the hero can do amazing things with a weapon, within reason, that’s ok. These amazing feats of battle prowess should be kept to a minimum or at least require some special circumstances or a cool down so to speak. If the hero can kill a hundred men at a hundred yards with a longbow in less than a minute, the novel will be short.
Above all else, do not use television or movies as a blueprint or for research. Hollywood rarely gets these things right because they have explosions and cool, dramatic music to misdirect your eyes and mind. They can afford to be as far from accurate as they want because people will still watch a man throw knives and hit a bulls eye at 100 yards while rolling through explosions. I know I would.
That’s a lot to consider and probably added at least a few days to your research. It will be worth it. I’ll break things down a bit more to help.
Is there an army? What’s the army’s purpose? Who runs the army?
Typically, an army serves one of two purposes. An army either conquers or defends. Most armies could do both, but that might stretch the ranks a bit thin. The size of the army doesn’t matter at this point, but you should begin developing an idea of the size of the army. While you’re at it, will this army be an evil army or fighting for the good guys?
The people in charge of the army are as important as the army itself. You’ll get a deeper story and be able to write better battle scenes if some of your minor characters interact with your protagonist or antagonist. Develop a general or commander to oversee the army. Give that character a minor character or two to abuse or praise. Perhaps this can be a beloved son of the king that dies in a battle or defects to the enemy.
Be sure to get the ranks right. Sure, you are writing fiction, but people will relate and understand the story better if some things are familiar. You wouldn’t call a purple fruit shaped like a banana an orange in your story because it would confuse and annoy your readers. The same applies to ranks in your army.
It’s not a critical point, but a minor point to consider are where does the army get soldiers. Are they drafted or do they volunteer? This can be valuable plot material if the army is evil. For instance, the protagonist and the antagonist might be drafted into the same evil army, but the protagonist breaks free and becomes a resistance leader while the antagonist kills his way to becoming general of the army. The scenarios are endless.
What kind of technology, weapons and armor does the army have access to?
Technology needs to be believable even if it’s not accurate. At the time of the original series, the technology we saw watching Star Trek was pure fantasy, but we could believe in it. Technology allows for the greatest creative license, but don’t take it past any limits. Technology needs to mesh and fit in with all the other technology. An herbalist using a mortar and pestle to grind herbs for medicine wouldn’t have access to x-rays.
Weapons all work in specific scenarios. Spears are rarely thrown like we see in movies. A man with a spear and a shield is more likely to kill a man with a sword or dagger in a one on one fight; provided he has been trained of course. Every weapon has a use and that use is usually to counter another weapon. Cavalry counter swordsmen and archers counter both usually.
Armor is designed to counter weapons and protect vital organs. Leather armor reduces damage from slicing weapons and offers a little padding against blunt weapons. Metal armor counters everything except crushing blows and penetrating blows. Spears and arrows would penetrate leather and metal armor and a 300-pound boulder dropped on a soldier ends their fight.
Wait, what about magic?
This is where reality breaks down and you get to go wild. Magic can be a powerful and one of your army’s best weapons. Magic should not be all powerful however. If the people wielding the magic can snap their fingers and knock over a horde of charging cavalry, the novel would wind up being pretty short. They can simply walk across the battlefield snapping their fingers until the battle is won.
Limit magic to its source or saddle the wielder with consequences. Let’s say sorcerers can only cast fireballs if they have some ultra-rare spell materials or the magic user uses a relic of some sort that needs to recharge between uses. One of the most often used mechanics of magic is the all magic comes with consequences magic. Casting a spell that disintegrates an opponent might take a year from the life of the caster or fireballs burn the caster a little.
The twists and turns of writing the military in your novel are countless. That may seem daunting, but if you follow the basic rules of war and do the research, you can write in a solid, believable military. A good place to start is looking into military history where it pertains to your novel. Learn about their armor, weapons and tactics. Your story will be better and you’ll feel better knowing you wrote it that way.