How Do Cannons Affect Your Naval Combat?

Recently, I went over the naval tactics your characters might use in a world without gunpowder. This raises the natural question, what happens when gunpowder is introduced? As you might imagine, the answer is complicated. Gunpowder isn’t a single toggle switch. There are hundreds, possibly thousands, of innovations and changes that your setting could go through thanks to this explosive compound, even just within the realm of naval combat.

To keep this article to a manageable length, today we focus exclusively on the effect of cannons on maritime battles before the introduction of steam engines. That means we need to determine how the cannons in your setting work and the ways they’re used. Once you’ve got that sorted out, you can describe broadsides and recoil to your heart’s content.

How Powerful Are They?

We tend to think of cannons as great iron monsters, belching fire and tearing the mightiest fortifications apart at will, but cannons didn’t start out that way. If your world mirrors our own history, the first cannons will be relatively small, certainly not powerful enough to cause structural damage to a ship.

If these smaller cannons are the norm, then their main effect will be as a weapon against the enemy crew prior to boarding. They can make a big impact on the battle, but the action will still be decided in hand-to-hand combat.

Once cannons get powerful enough to cause structural damage to another ship, boarding becomes less common as ships stand off at a distance and bombard each other instead. Note that this switch probably won’t be made all at once, and it may take tactics some time to catch up with technology.

That’s what happened to the famous Spanish Armada in 1588. The Spanish admirals assumed the battle would be decided by boarding, so they packed their ships with soldiers and tried to close in. Meanwhile, the English kept their faster ships at a distance and pelted the Spanish with cannon fire. As a result, England remained notably unconquered.

However, even with more powerful cannons, it won’t be common for ships to actually sink during the battle. More likely, ships will take enough damage that they can’t fight any longer and then be sunk or captured afterward. Historically, it wasn’t until the development of the explosive shell that sinking ships in combat became common, and that technology is beyond what we’re talking about today.

What Are They Made Of?

It won’t surprise you that the material used to build a cannon has a lot to do with the cannon’s capabilities. While it is technically possible to make a cannon out of wood, most will be made of metal, and the two prominent metals for this task are bronze and iron.

Bronze cannons have a number of major advantages. For one, they’re lighter, which is confusing since bronze is actually heavier than iron. Even so, historical casting techniques meant that bronze cannons could be made with thinner walls, and it’s likely to be the same in your world unless you feel like getting really into the weeds of metalwork.

Another advantage of bronze is that it doesn’t rust, whereas iron cannons have to be regularly cleaned due to oxidation from the salty sea air. Bronze cannons also require less extensive facilities to make. But the most notable advantage of bronze is that it’s more flexible than iron, so it won’t randomly explode under the pressure of being fired the way iron cannons do. You can bet that makes a big difference to the people who crew these weapons.

Iron has exactly one advantage over bronze, but it’s a big one: cost. Iron is simply much easier to find,* and historically, an iron cannon would often cost a third or even a fourth as much as its bronze equivalent. Weight isn’t as big a factor for ships as it is on land, and the lower cost means iron cannons are likely to be the norm once facilities to cast them are commonly available, explosions be damned. After all, the people ordering naval guns are rarely the ones who have to operate them.

With advanced metalworking techniques, it is possible to reduce or eliminate the risk of explosions in iron cannons. You can see this in historical weapons like the distinctively curved Dahlgren guns, which were specifically designed with safety in mind. But just like exploding shells, these weapons aren’t likely to appear within today’s timeframe.

Where Are They Mounted?

In addition to power and construction material, where a cannon is placed on a ship says a lot about how it will be used. There are basically two choices – the front or the sides – but deciding which one your navies will opt for is no simple feat.

Cannons placed at the bow of a ship have the major advantage of being easy to aim. You just point the ship at whatever you don’t like and let the round shot fly. The drawback is that there isn’t room for more than a handful of guns on a ship’s prow. A ship’s sides, on the other hand, can hold a LOT of cannons, hence the term “broadside.” The problem is that weapons pointed sideways are a lot harder to aim.

With these tradeoffs in mind, front-facing cannons are likely to dominate as long as the cannons themselves are rare and expensive. That way, it doesn’t matter if you can’t fit more than three or four per ship – you couldn’t afford more than that anyway. Fewer cannons also means they can be mounted on oar-powered galleys, which aren’t great for broadsides since they have all those oars in the way. Rowed ships make front-facing guns even more accurate since captains don’t need to depend on the wind to steer their ships.

However, once cannons get cheap enough, all the advantages of mounting them forward go out the window in favor of the sheer weight of fire that a broadside can bring to bear. Not only is there more room on a ship’s sides, but you can add extra gun decks for even more cannons. Historically, this transition played out in the Mediterranean and Indian Oceans, as formerly dominant Ottoman galleys eventually gave way to the tall ships used by other European powers.

That’s not to say there are no drawbacks to a broadside. For one thing, cutting holes in the ship’s side for gunports requires a sturdy hull, and the higher up you place heavy cannons, the less stable your ship gets. Expect your navy to lose more than a few vessels as they lean too far over and water flows in through the open gunports. More guns also make for a heavier ship, requiring a lot of sail to move at any speed. Plus, getting the sides of a ship into position to fire on the enemy is no simple task and requires a lot of maneuvering. Even so, side-mounted cannons provide so much firepower that these downsides are likely to be ignored.

It’s entirely possible that your ships might have cannons on the front and sides, but in most cases, one or the other will constitute the primary armament. Why no guns on the stern, you ask? Largely because a ship’s stern will typically have the least armor, and so pointing it at the enemy is a bad idea in any case.

Are the Crews Well Trained?

While cannons might look simple, operating them is anything but. It requires a team of gunners working in tandem, and their skill level will have a huge impact on the battles in your setting. The first thing to think about is aiming, which is a whole process in and of itself.

Unless your cannons are a lot more advanced than their real-world counterparts, all aiming is done by hand. To change elevation, gunners adjust a wooden block under the cannon’s breech, which is relatively straightforward. Moving side to side is another issue entirely and requires the incredibly scientific method of shoving the cannon into place with crowbars. You can see how it would be easy for inexperienced crews to over- or under-compensate.

Assuming you can get the gun properly aimed, there’s the timing of the shot to consider. Ships at sea have a habit of rolling with the waves, which changes the cannon’s elevation. Fire when the cannon is too high, and you overshoot. Fire when it’s too low, and you only scare some fish. That said, experienced gunners can use higher elevation to shoot farther, and even use a low elevation to skip cannonballs off the water and into the enemy. That last one sounds made up, but it has historical precedent. Even so, it may come across as cartoonish to audiences, so use with caution.

Once the cannon’s been fired, the crew has to deal with recoil. This is no small matter, as a gun weighing up to three tons suddenly leaps back against its harness. Gunners who stand in the wrong place can easily be maimed or killed. If it breaks free, it is a “loose cannon” and everyone is in for a bad day.

If the recoil goes well, the reloading begins. Fresh powder is brought up from the magazine, then rammed down the barrel and followed by the shot. That sounds simple, but the trick is to do it over and over again in quick succession. A well-trained crew can get somewhere between three shots every five minutes to possibly one shot per minute,* while less experienced gunners will struggle to make half that.

Gunners have to do all this in cramped, poorly lit* conditions, with deafening explosions all around them. You can see why training would have such a big impact on the outcome of a fight.

What Are They Aimed At?

If there’s one thing I emphasize in my ship-related posts, it’s that ships are complicated. There are a nearly infinite number of parts and components for your gunners to aim at, and that number only grows if you look outside the commonly cited European Age of Sail. Fortunately, for storytelling purposes, we can focus on just three categories: hull, rigging, and crew.

The hull is the actual body of the ship, and shots aimed there are meant to do structural damage, along with taking out both enemy guns and their gunners. For this type of work, the standard round shot is used, also known as a cannonball. Enemy crew not struck directly by incoming shot are often hit by spear-sized splinters instead, which can result in truly horrific injuries, so describe with care. While ships at this tech level aren’t likely to actually sink from the hits they receive, firing at the hull is the fastest way to destroy the enemy’s ability to fight back.

Firing at the rigging, on the other hand, does significantly less damage to both ship and crew.* Instead, the goal is to reduce the enemy’s speed by destroying lines, sails, spars, and possibly even a mast if you’re lucky. While it’s technically possible to render an enemy completely immobile and thus helpless, it’s unlikely, so this method is generally used as a prelude to escape. As for ammunition, round shot can work, but for the best results, more specialized options like chain shot and bar shot are available. These are essentially a cannonball split in half and connected by either a chain or a bar, respectively, and the wider area increases the chance of catching something in the rigging.

Finally, there’s the possibility that your ships will have to fire directly at the enemy crew. This is most likely to happen just before boarding and usually done with grapeshot or canister shot, essentially a container of musket balls that turns the cannon into a giant shotgun. If ammunition is low, cannons can be loaded with nails, iron fragments, and any other bits of debris.

Grapeshot is devastating against a packed enemy, and like the splinters from earlier, it can cause some truly horrific wounds on the human body. How much detail you want to use there depends on how dark you’re looking to make the story.

How Well Armored Is the Target?

The final consideration isn’t about the cannons themselves but what they’re firing at. For the most part, this will be the wooden sides of other ships. Barring inferior building techniques, these sides will be quite strong, able to repel cannon fire except at close range. At that range, however, there isn’t a lot of protection available, and the battle largely comes down to who can shoot faster and more accurately.

Metal armor is a possibility, but it will probably be extremely rare. For one thing, metal is heavy and puts a real strain on sail- or oar-powered ships. But more importantly, producing iron in the quantities necessary for armor is simply beyond the reach of most navies unless your setting has gone through something akin to the industrial revolution. The Korean turtle ship does exist as a historical counterpoint, but it’s unclear whether its armor was really used to repel cannon fire or only meant to deter boarders.

Even so, it’s entirely possible that the crews in your setting might create some ad-hoc metal armor for their ships, especially before a difficult battle. There are a few historical accounts of wooden ships using lengths of iron chain as additional protection, so it’s entirely believable that something similar could happen in your setting. This makeshift armor wouldn’t be nearly as effective as a true ironclad, but it might do in a pinch.

Where a ship is struck can also affect how much damage is done. I mentioned a ship’s sides before, but in most cases, being struck on the bow or the stern is significantly worse. For one thing, those areas tend to have less protection, especially the stern. A sailing ship’s stern is likely to be open and full of windows, sometimes for engineering purposes, other times because the captain wanted a nice view.

Beyond the weaker armor, a shot that penetrates the bow or stern can travel the entire length of the ship, wreaking havoc all the way. This type of attack is called raking, and it’s a devastating way to win a battle.

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Just like with my previous posts about ships, it’s possible to go into a lot more detail than we’ve covered today. I haven’t even mentioned the line ahead or the line abreast formations yet, to say nothing of the horrors that are naval medicine. But for now, you’ve at least got the basics of how cannons work, and that’ll be enough for the level of detail most stories want in their naval battles.