Got a Real-World Weapon, Armour or Tactics Question? Mk. XXVIII

[Brother Oni]

Real World Weapon, Armour and Tactics Thread XXVIII

This thread is a resource for getting information about real life weapons, armour and tactics. The concept has always been that the information is for RPG players and DMs so they can use it to make their games better, thus it's here rather than in Friendly Banter.

A few rules for this thread:

• This thread is for asking questions about how weapons, armour and tactics really work. As such, it's not going to include game rule statistics. If you have such a question, especially if it stems from an answer or question in this thread, feel free to start a new thread and include a link back to here. If you do ask a rule question here, you'll be asked to move it elsewhere, and then we'll be happy to help out with it.
• Any weapon or time period is open for questions. Medieval and ancient warfare questions seem to predominate, but since there are many games set in other periods as well, feel free to ask about any weapon. This includes futuristic ones - but be aware that these will be likely assessed according to their real life feasibility. Thus, phasers, for example, will be talked about in real-world science and physics terms rather than the Star Trek canon. If you want to discuss a fictional weapon from a particular source according to the canonical explanation, please start a new thread for it.
• Please try to cite your claims if possible. If you know of a citation for a particular piece of information, please include it. However, everyone should be aware that sometimes even the experts don't agree, so it's quite possible to have two conflicting answers to the same question. This isn't a problem; the asker of the question can examine the information and decide which side to go with. The purpose of the thread is to provide as much information as possible. Debates are fine, but be sure to keep it a friendly debate (even if the experts can't!).
• No modern real-world political discussion. As the great Carl von Clausevitz once said, "War is merely the continuation of policy by other means," so politics and war are heavily intertwined. However, politics are a big hot-button issue and one banned on these boards, so avoid political analysis if at all possible (this thread is primarily about military hardware and tactics). There's more leeway on this for anything prior to about 1800, but be very careful with all of it, and anything past 1900 is surely not open for analysis (These are arbitrary dates but any dates would be, and these are felt to be reasonable).
• No graphic descriptions. War is violent, dirty, and horrific, and anyone discussing it should be keenly aware of that. However, on this board graphic descriptions of violence (or sexuality) are not allowed, so please avoid them.
• A few additional comments following the premature demise of thread XXVI: Words from Roland St. Jude.

With that done, have at and enjoy yourselves!

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[hymer]

I'm looking for some inspiration on a coming fight at a ford, pre-gunpowder.

With that in mind, if a small force are holding a ford against enemy raiders and scouts, what are some things to take into account when deploying said force? They may need to be there for days, and there is no certainty which side the enemy might try to attack and/or sneak across from. Any interesting and illuminating accounts of skirmishes at fords I might read for ideas?

[Kiero]

I'm looking for some inspiration on a coming fight at a ford, pre-gunpowder.

With that in mind, if a small force are holding a ford against enemy raiders and scouts, what are some things to take into account when deploying said force? They may need to be there for days, and there is no certainty which side the enemy might try to attack and/or sneak across from. Any interesting and illuminating accounts of skirmishes at fords I might read for ideas?

Why are they holding the ford? Does the geography make it the only viable crossing, or could an enterprising foe make their own passage by other means (eg pontoon bridge)? How capable are the defenders, can they prepare measures to slow the enemy, such as putting up stakes? How good is their communication with other elements of the defending force? How big is the mobile reserve which could respond either to reinforce the ford, or defend alternate crossings? Could the attacking force attempt a night-time crossing?

[hymer]

Why are they holding the ford?

Opportunism is their leader's main motivation. They are part of a loose confederation of tribes allied against invaders. Holding the ford is good for charging tolls or picking up slaves. The defenders will have to concentrate their forces once/if the enemy gets closer with their main force. In the mean time, it's skirmishing and trying to prevent/delay the invaders finding out about the lay of the land, and what they are up against exactly.

Does the geography make it the only viable crossing, or could an enterprising foe make their own passage by other means (eg pontoon bridge)?

That can be decided according to what would be more interesting or appropriate. But it is at least the best crossing in the general area, let's say within a day's march.

How capable are the defenders

No more capable than a group of PCs can rout them. But then, five or six heroes do make for quite a force.

can they prepare measures to slow the enemy, such as putting up stakes?

They can, if it makes for a more interesting encounter. They may have taken over from a more industrious group.

How good is their communication with other elements of the defending force?

Sluggish. I intend for there to be an initial encounter where the PCs seize the ford. And then two or three encounters when others try to recapture it. Then the PCs' allies will arrive and cross, and they'll all be on their way out of the area as fast as they can. So the ford guards should manage to get help within a few hours, although that may come down to someone else coming by to check up on them. Possibly someone better organized if the initial fight is easy.

How big is the mobile reserve which could respond either to reinforce the ford, or defend alternate crossings?

Perhaps three to five times the small force holding the ford. But they'd rather not commit them all to the ford if they can avoid it, especially since the PCs are not with the main invaders.

Could the attacking force attempt a night-time crossing?

Absolutely.

[fusilier]

It’s not an acceptable risk for reenactors in the present day.

And Sharpe is the first time I heard of spit loading. Tap loading maybe. But until I see a better source, I just don’t believe it. Especially for the Rifles, who should have been more concerned with accuracy than rate of fire, and should have demonstrated better weapon handling

“Don’t point it at your face” is pretty much rule one, not some overly cautious nagging

Yeah, the manuals of the day had the soldiers return the ramrod with your pinky finger, to prevent putting your hand over the muzzle of a loaded musket.

And rifles need a tight fitting ball -- I can't imagine that it would be possible to spit load (or tap load) one. Maybe if they carried undersized balls for rapid fire? But I haven't heard of that in the Napoleonic period.

However, poor training among soldiers was also all too common. In the early 1850s when a group of US regulars had their old weapons replaced with new ones, some inspectors-general happened to be on hand to inspect the old weapons before they were cleaned. Something like half of the weapons they inspected had been loaded incorrectly, with the ball placed down the muzzle first, and the powder poured on top!

[Mike_G]

Yeah, the manuals of the day had the soldiers return the ramrod with your pinky finger, to prevent putting your hand over the muzzle of a loaded musket.

And rifles need a tight fitting ball -- I can't imagine that it would be possible to spit load (or tap load) one. Maybe if they carried undersized balls for rapid fire? But I haven't heard of that in the Napoleonic period.

However, poor training among soldiers was also all too common. In the early 1850s when a group of US regulars had their old weapons replaced with new ones, some inspectors-general happened to be on hand to inspect the old weapons before they were cleaned. Something like half of the weapons they inspected had been loaded incorrectly, with the ball placed down the muzzle first, and the powder poured on top!

I totally buy bad training. I mean, in Vietnam some early M 16s were issued without cleaning kits and troops were told they didn't need them, the rifle was "self cleaning" which simply isn't a thing.

But these guys are the Rifle regiment, so marksmen who should know about guns and shooting, and a group of "chosen men" so the best of the Rifles.

And I've been a history nerd all my life and never encountered spit loading before reading Cornwell. It sounds like something a guy who doesn't spend a lot of time on the range would think is cool and unique to put in a book. But putting your face in front of the muzzle of a gun after you just primed the pan and pour powder down the barrel is a red flag range violation everywhere. I can't see a Somali pirate thinking that's safe, let alone a sharpshooter.

In the movie "The Crossing" about Washington's sneak attack on Trenton, a sharpshooter loads his rifle and then dribbles candle wax over the lock to keep the powder dry. It's an interesting idea, but I never saw it elsewhere so it seems more like something s screenwriter would think was cool to include than something a sharpshooter would do, ie waving a candle around a loaded black powder musket.

So to me, "Cornwell put it in a book" seems more "Rule of Cool" than "Supported by Fact." And the fact a a reenactor tried it just says "some reenactors are really dumb." As well as the fact that the Rifles reenactors only cite Sharpe as a source, not any kind of historical manual or primary source like a period letter or whatever.

Vizzini's third classic blunder should be "never take safety advice from a Sean Bean character."

[KineticDiplomat]

Cornwell put it in a book was more a “for the loose purposes of historical fiction, and its RPG counterpart, you have more than enough to go with here, regardless of the swirling academic debate”.

Re: the ford.

A few things that may help a clever PC group:

1. How are the defenders feeding themselves? You can only carry so much food on your (or your horse’s) back, cooking and eating take time, and if they are “living off the land” there are entire cycles of foraging, hunting, gathering, and food preparation that should create opportunities.

2. Given it is a tribal confederation, what’s the command structure look like? Does the leader owe loyalty to the confederate whole, just his tribe, a specific tribal leader? Is he a young man out to show he’s got bones, take loot, earn some wife-rights - the type that maybe gets ansty without action, maybe sees “hold the ford” less as hold the ford and more as “engage in glorious battle with anyone near the ford”? Is he an old passed over man who just wants this to be quiet, and is barely doing more than camping by the river?

3. How are they talking to the main body? Are they sending back messengers? Completely isolated? Using signal fires the PCs can see?

A few things that may hinder the PCs:

1. Depending on the force size, a few scattered patrols or scouts on the far side, maybe even a foraging party may alert the defenders, harass the PCs, or even fight a delaying action. Now the PCs have to race against the clock to clear the ford.

2. A layered kill zone. The far side of the ford is blocked up with barricades like logs, brush, and ditches - maybe just a shield wall - but something to bottle the PCs in the ford itself as they fight. Depending on the tech/magic level, there could be obstacles below the water surface, tripping, snaring, and slowing movement through the ford. And if you have missile troops that can overwatch from a flank or high position, they can shoot the attackers apart as they struggle through the water.

3. Let the PCs out into a killing cup. Basically, you know the PCs have to cross on a given line, hence the ford. You can let them drive head, bowing the line around their axis, then fall on them from multiple sides.

[Pauly]

I'm looking for some inspiration on a coming fight at a ford, pre-gunpowder.

With that in mind, if a small force are holding a ford against enemy raiders and scouts, what are some things to take into account when deploying said force? They may need to be there for days, and there is no certainty which side the enemy might try to attack and/or sneak across from. Any interesting and illuminating accounts of skirmishes at fords I might read for ideas?

One incident from Napoleon’s 1809 Austrian campaign comes to mind. At one of the smaller battles the French were looking to Ford the river, but didn’t know where the ford was. They noticed that a stretch of river had an artillery battery deployed facing it.

They made the assumption that the only reason to defend that part of the river was that it must have been where the ford was, attacked and crosssed there.

[The Jack]

Swiss Alpenflage, Belgian Jigsaw, Rhodesian bushstroke (to a lesser extent)

are there any other camouflage patterns where you look at them up close and think 'nope, that'd never work' but then which get absurdly effective with a little bit of range?

Because I think they're works of genius.

[Pauly]

Swiss Alpenflage, Belgian Jigsaw, Rhodesian bushstroke (to a lesser extent)

are there any other camouflage patterns where you look at them up close and think 'nope, that'd never work' but then which get absurdly effective with a little bit of range?

Because I think they're works of genius.

The rifle green of the Rifle Regiments and the Ghurkas in the 19th C. To my mind was amazing. Turns a man crouching/kneeling in an open field into a bush. The Ghurkas kept their rifle green for quite a while after the rest of the British and Indian armies had moved onto khaki.

[fusilier]

I totally buy bad training. I mean, in Vietnam some early M 16s were issued without cleaning kits and troops were told they didn't need them, the rifle was "self cleaning" which simply isn't a thing.

But these guys are the Rifle regiment, so marksmen who should know about guns and shooting, and a group of "chosen men" so the best of the Rifles.

And I've been a history nerd all my life and never encountered spit loading before reading Cornwell. It sounds like something a guy who doesn't spend a lot of time on the range would think is cool and unique to put in a book. But putting your face in front of the muzzle of a gun after you just primed the pan and pour powder down the barrel is a red flag range violation everywhere. I can't see a Somali pirate thinking that's safe, let alone a sharpshooter.

In the movie "The Crossing" about Washington's sneak attack on Trenton, a sharpshooter loads his rifle and then dribbles candle wax over the lock to keep the powder dry. It's an interesting idea, but I never saw it elsewhere so it seems more like something s screenwriter would think was cool to include than something a sharpshooter would do, ie waving a candle around a loaded black powder musket.

So to me, "Cornwell put it in a book" seems more "Rule of Cool" than "Supported by Fact." And the fact a a reenactor tried it just says "some reenactors are really dumb." As well as the fact that the Rifles reenactors only cite Sharpe as a source, not any kind of historical manual or primary source like a period letter or whatever.

Vizzini's third classic blunder should be "never take safety advice from a Sean Bean character."

Agree 100% about the riflemen being elite, well trained soldiers, and as I pointed out spit-loading makes even less sense for a rifle. I was just pointing out that spit-loading *may* have been done, even if the particular context presented in the Sharpe's series makes no sense. (But, as you said, we should really see the original sources for such practice.)

One of the things that I've heard, but haven't been able to track down a good source on, is the claim that they sometimes skipped priming. The vent hole was drilled large, allowing powder to escape from the barrel to pan, the soldier giving the musket a good flick of the wrist to shake some powder into the pan. The pan still had to be closed, but the fiddly bit of pouring the right amount of powder out of a paper cartridge is skipped. I've seen this done, and it can work surprisingly well, but I would still rather have a contemporary source for it.

I might want to look into the wax thing; I have heard of similar things, although I am concerned about molten wax coming in contact with powder. On the other hand, concerning waving a candle around a loaded musket . . . I have used a matchlock!!

I'm constantly learning new things, even about things I thought were well understood. Probably too esoteric for this board but there's a debate in the ACW reenactor crowd about oblique firing that may overturn how it's been interpreted for decades.

[snowblizz]

I might want to look into the wax thing; I have heard of similar things, although I am concerned about molten wax coming in contact with powder. On the other hand, concerning waving a candle around a loaded musket . . . I have used a matchlock!!

The wax thing I remember has cropped up before in these threads. Just can't recall the context.

Wax won't be hot enough to set of the powder, and you are presumably waxing the outer parts of the mechanisms like the lock which should be fairly safe. As safe as wielding a matchlock anyway around loose powder.

[Mike_G]

Agree 100% about the riflemen being elite, well trained soldiers, and as I pointed out spit-loading makes even less sense for a rifle. I was just pointing out that spit-loading *may* have been done, even if the particular context presented in the Sharpe's series makes no sense. (But, as you said, we should really see the original sources for such practice.)

One of the things that I've heard, but haven't been able to track down a good source on, is the claim that they sometimes skipped priming. The vent hole was drilled large, allowing powder to escape from the barrel to pan, the soldier giving the musket a good flick of the wrist to shake some powder into the pan. The pan still had to be closed, but the fiddly bit of pouring the right amount of powder out of a paper cartridge is skipped. I've seen this done, and it can work surprisingly well, but I would still rather have a contemporary source for it.

I might want to look into the wax thing; I have heard of similar things, although I am concerned about molten wax coming in contact with powder. On the other hand, concerning waving a candle around a loaded musket . . . I have used a matchlock!!

I'm constantly learning new things, even about things I thought were well understood. Probably too esoteric for this board but there's a debate in the ACW reenactor crowd about oblique firing that may overturn how it's been interpreted for decades.

I'm not saying tap loading never happened. My issue is just with spitting the ball down the barrel, since it's risky (I will never accept that pointing the muzzle at your own damn face is anything but stupid and negligent) but has no significant payoff even if the slim chance of blowing your head off seems like a reasonable risk.

Tap loading eliminates the need to ram the ball down, which clearly saves a significant amount of time, including drawing and replacing the ramrod. And if it shakes powder into the pan, it saves the step of priming, so it probably increases your rate of fire by a lot.

But how much time do you actually save by spitting the ball into the barrel versus putting it there with your fingers?

The concept annoyed me when I first read "Sharpe," especially since the rifle needed a tight fit, and was really short, so you can't put the butt on the ground and spit a ball into it unless you basically kneel down.

I just thinks it's stupid and dangerous and unsupported by any source material and ineffective and probably never done by the Rifles, if it was done at all. It really kinda soured me on Cornwell.

[Kiero]

I can see why tap-loading (just in terms of not using a ramrod) could speed things up for a smoothbore musket.

However, rifles have grooves which give the ball a snug fit, I don't think gravity and a tap alone would make the ball fall all the way to the bottom of the breech. Even moreso if the barrel is already fouled from previous firing.

[Aneurin]

While I don't know of a source that says spit-loading the rifle actually happened, I don't think it's all that implausible.

It might sound stupid and dangerous to put your face over the barrel of a charged (and soon to be loaded) gun, but so does urinating in the barrel of a musket or rifle to clear the caked powder. So does crawling under the engines in mills to clear jams by hand while the engines are working. The world was very different back then, and didn't care much for health and safety laws - in fact, it didn't have any.

Spitting the ball into the barrel has one significant advantage over loading by hand, which is that it requires less movements to complete and there is less opportunity for tired and cramping fingers to fumble and drop the ball while trying to move it from mouth to barrel. Every movement, and every opportunity to fumble, you can cut out is an advantage as it means fewer mistakes and even a fraction of a second could be enough for you to fire before the enemy does. I believe that the official British musket drill was mostly shortened by veteran regiments, who took shortcuts in order to increase their rate of fire as the official drill was slow and complicated - spit-loading sounds like another one of those short cuts, not the "right" way of doing things but something that probably was done on the battlefield.


Re: tap loading the rifle, the rifle balls were encased in leather to make them snug enough that the rifling would be effective. By leaving the leather off, or using regular musket balls, you could tap load the rifle - though it would be a bit inferior to the Brown Bess and lose the accuracy and range of the rifle, in exchange for a significantly higher rate of fire.

[fusilier]

Re: tap loading the rifle, the rifle balls were encased in leather to make them snug enough that the rifling would be effective. By leaving the leather off, or using regular musket balls, you could tap load the rifle - though it would be a bit inferior to the Brown Bess and lose the accuracy and range of the rifle, in exchange for a significantly higher rate of fire.

That's a good point! If they were using patches to make up the windage (rather than simply a tight fitting ball), then it may be just loose enough for spit/tap-loading if they discarded the patch. I'm not too sure about this though: researching the Baker rifle the windage doesn't look all that great (although I'm seeing conflicting information). The Brown Bess, on the other hand, used a .69 caliber ball in a .75 caliber barrel.

Mike_G: I'm not disagreeing with you, I think you are bringing up good points. Clearly this has struck a nerve. ;-)

[Gnoman]

I don't remember the title, but I remember reading a novelized story about an underage Civil War drummer boy which featured spit loading. IIRC, it was written in the 50s and predates the Sharpe books.

[Mike_G]

I don't remember the title, but I remember reading a novelized story about an underage Civil War drummer boy which featured spit loading. IIRC, it was written in the 50s and predates the Sharpe books.

It makes even less sense with a Minie ball.

[Gnoman]

Not going to argue with you there, just pointing out that I'd seen it in an earlier work.

[Mike_G]

I'll have to just let this go, but as a guy who learned about gun safety in the Marines, and who has worked two decades as a paramedic, I just can't wrap my head around the idea of putting your face over the muzzle of a loaded gun, then banging the loaded weapon with a half-**** safety on the ground, hoping you seat the ball safely.

My mid swims with images of headless reenactors.

[snowblizz]

It makes even less sense with a Minie ball.

Not *all* civil war weapons used Minie balls though. Especially the South had to use both older and non-standard weapons due to shortages.

Plenty of older vintage, and even shotguns, used.

Still agree it seems weird.


I am having trouble even picture how it works. It can't be "spit" the way I imagine it because that'd mean you're trying to hit a tiny hole at distance.....

[Brother Oni]

I am having trouble even picture how it works. It can't be "spit" the way I imagine it because that'd mean you're trying to hit a tiny hole at distance.....

I can think of a number of adult videos that can help with the visualisation.

[Grim Portent]

I am having trouble even picture how it works. It can't be "spit" the way I imagine it because that'd mean you're trying to hit a tiny hole at distance.....

I think the idea is; hold bullet in mouth, raise gun to mouth or bend/crouch to bring mouth to gun, spit bullet down barrel of gun from point blank. Obviously this means the gun barrel is pointed at the face, which is generally ill advised.

As opposed to say spitting a cherry pit a dozen paces or trying to hawk a blob of phlegm into a spittoon across a saloon.

[fusilier]

Not *all* civil war weapons used Minie balls though. Especially the South had to use both older and non-standard weapons due to shortages.

Plenty of older vintage, and even shotguns, used.

Still agree it seems weird.


I am having trouble even picture how it works. It can't be "spit" the way I imagine it because that'd mean you're trying to hit a tiny hole at distance.....

The rifle-musket was relatively new in the US at the outbreak of the war, most going to small regular army. As a result large numbers of smoothbores and rifled muskets* were used by both sides. After the fall of Vicksburg some of Grant's regiments were able to exchange their French/Belgian smoothbore muskets for Enfield rifle-muskets captured from the Confederates. So sometimes the Confederates were better equipped than the Yankee opponents. Despite some early problems which beset both sides, the Confederates seem to have done a reasonable job of equipping their army with modern firearms.

I haven't seen any original references to spit-loading, and I know of no ACW reenactors who have promoted it. My initial understanding of it was to simply blow/spit down the barrel and hope that seats the ball at the base (if it doesn't the barrel could explode). But reading about it here, it sounds like the ball was actually placed in the mouth, then spit down the barrel? I'll admit, I never studied it much, because I never took the concept too seriously . . .

*A "rifled musket" is a smoothbore musket that was subsequently rifled. A "rifle-musket" was produced with rifling. This distinction is often lost, even on period documents -- only pedantic ordnance officers seem to have respected the difference. Rifled muskets were typically of a larger, less efficient, caliber than the rifle-muskets. Also, as smoothbore weapons were not designed to be rifled, the act of rifling made their barrels effectively thinner, which reduced the amount of powder that could be safely used. This led to a further deterioration of the ballistic properties.

[Mike_G]

I haven't seen any original references to spit-loading, and I know of no ACW reenactors who have promoted it. My initial understanding of it was to simply blow/spit down the barrel and hope that seats the ball at the base (if it doesn't the barrel could explode). But reading about it here, it sounds like the ball was actually placed in the mouth, then spit down the barrel? I'll admit, I never studied it much, because I never took the concept too seriously . . . .

I don't think many people did. Until bloody "Sharpe's OSHA Violation" or whatever book one of that series is.

It's dumb and dangerous and doesn't shave much time off the loading process. I'm sure somebody did it, because people are stupid, but I doubt it was ever widespread or authorized.

But now there are a number of reenactors courting a 69 calibre lobotomy because Sean Bean made it cool.

[rrgg]

I think it's specifically the spitting part that doesn't make much sense to me. Going back to even earlier treatises though I have definitely found complaints about soldiers using bullets small enough that they don't need to use the ramrod.

[fusilier]

I think it's specifically the spitting part that doesn't make much sense to me. Going back to even earlier treatises though I have definitely found complaints about soldiers using bullets small enough that they don't need to use the ramrod.

We've discussed this before, the so called "rolling gauge" bullets, and even De Gheyn's manual (circa 1610) makes a comment about drawing the ramrod *if* you are using one. It does not, of course, mention spitting down the barrel. While there's enough evidence to convince me that sometimes soldiers loaded loose ammo without using the ramrod, I still haven't seen anything to support spit-loading.

Trying to check this up on the internet, it is invariably frustrated by references to Sharpe's rifles, rather than primary sources. I did find a discussion, which includes two Napoleonic era references to what could be described as "tap-loading" but they did NOT involve spitting.

http://theminiaturespage.com/boards/msg.mv?id=330789

[Shepsquared]

Question relating to ships, particularly in the (early?) medieval period where ships like cogs became widespread: would a fireball spell be a ship killer? Would it just burn away the mast and set some parts of the deck one fire, which sailors could deal with? Or was everything on a ship very fireproof?

[Mr Beer]

Question relating to ships, particularly in the (early?) medieval period where ships like cogs became widespread: would a fireball spell be a ship killer? Would it just burn away the mast and set some parts of the deck one fire, which sailors could deal with? Or was everything on a ship very fireproof?

OK, so we have to specify system and edition, so let's do this:

D&D 5e Fireball spell "ignites flammable objects in the area that aren’t being worn or carried.".

Looks like a GM call to me. Medieval ships are not fireproof but may take precautions, especially if they expect to face fire weapons e.g. flaming arrows.

I think the sails and rigging are going up. A poorly run ship is going to have flammable material on deck (e.g. buckets, rags, ropes etc. just lying around). A well run warship will not - stuff gets stowed. I would consider decking to be not very flammable so presumably is not going to just light up. Note that it looks like people probably aren't going to get ignited according to the spell description.

My ruling would be that a fireball directed at a 60' long cog around its' single mast is going to ignite the sail and rigging.

The crew of a well run ship will be able to cut down the flaming wreckage, saving the ship and mast, but they will be unable to get under power until they can re-rig the whole thing, making them vulnerable for quite some time.

A poorly run ship is going to be alight in a bunch of places and the crew probably won't be able to prevent the whole thing eventually going up in flames.

Basically, yes this would initially be a shipkiller if used against mediaeval cogs, were I running the game.

However, in a world with fireballs, war captains will enchant the sail and rigging or use exotic non-flammable construction materials or at the very least, hose everything down with sea water prior to a battle. That should change the situation.

[AdAstra]

Question relating to ships, particularly in the (early?) medieval period where ships like cogs became widespread: would a fireball spell be a ship killer? Would it just burn away the mast and set some parts of the deck one fire, which sailors could deal with? Or was everything on a ship very fireproof?

It would likely depend on the nature of the Fireball, but I can tell you that sailing ships were very, very flammable. Aside from the structures being made of wood, you had rope (often tarred for waterproofing), cloth, and other materials waiting to catch. In addition, most ships were waterproofed with pitch, which is usually either petroleum or plant-resin based. Needless to say, all of this basically makes your sailing vessel a floating torch with delusions of grandeur. In fact, shot heated to a glowing red was used by shore forts as very effective anti-ship munitions, one that could not be safely replicated on ships themselves due to the obvious dangers (though obviously that wouldn't apply here). Hell, even nowadays fires aboard ships are considered extremely dangerous, as even though the hulls are metal, there's usually lots of fuel aboard.

However, sailors were (and usually still are) very well aware of this fact, and usually were very well trained, or at least motivated, in fire prevention and management. While even a small fire left unattended might be able to doom a vessel, an attentive crew would quickly be smothering it with water and sand. Also note that getting solid, well-seasoned wood to do anything more than scorch is a lot harder than it would appear, and a great deal of the outer surface of a ship, including the sails/rigging, will likely be soaked with water, further hindering ignition.

As for fireball specifically, I will be using 5e's version of it, which is a 20 ft. radius sphere that spreads around corners and explicitly lights up flammable objects in the area. Depending on your definition of flammable you might have next to no effect (assuming you consider solid wood and/or or materials soaked with water to not be flammable), or literally everything on the outer surface of the ship set alight. Might not be so bad, except that the spell spreading around corners (and presumably through significant gaps) means you also may have to deal with everything on the inside, which is likely to be much drier, and still include many obviously flammable materials (hammocks, spare rope, etc.). And with that area of effect, there's no way most ships have a crew capable of adequately fighting the fire conventionally, even assuming they all survived the blast.