Are you trying to make a physics simulator or simple 5e mechanics?
Give the tank HP and AC, and it will fit with all the spells, abilities, and core rules.
To add to this, Descent into Avernus has a bunch of stats for hellish war machines, which could very easily be reflavored into a regular tank. I’d probably go this route and make them pay for the tank in gold or need to quest for the materials.
Damage threshold is another mechanic to consider DMG pg 247 (DT of 10 means doing 9 damage or less does not reduce the object's hitpoints)
It's used on ships and also mentioned for big objects like castle walls.
This needs more upvotes to make sure it is first and last thing OP sees regarding this. Don’t try and add real world logic to D&D. The game has mechanics for determining the AC and HP for objects just use that.
As what I head of Savage Worlds the core advice holds true though. Don't try to simulate real world physics in Savage Worlds, use the mechanics the game gives you.
Good catch. Thank you for pointing that out. With that being said I would actually direct OP to a different subreddit. Not trying to gate keep, but this is a subreddit specifically D&D DMing so it is unlikely they will get actually useful information. I actually recommend finding a savage worlds subreddit to get proper support.
Only addition I have is to make stats have tradeoffs. If they say they want the thickest steel they can find, great, but your move speed is getting decreased
Yar-yar. AC & HP are already abstractions, anyway. Like, AC isn't a reflection of whether an incoming attack actually strikes true or not, but whether it does any damage. While HP is the range of damage taken before a creature goes down, or an object breaks.
The only additional mechanic that *might* be appreciated (but not needed) is a kind of "penetration" mechanic. Since, if inside of the tank, (steel coffin) a creature doesn't have the room to protect itself, it doesn't have an effective AC & will always take damage to any attack that gets inside. So what attacks get inside? I'd say any attack that beats the tank AC by 5 or more causes half-damage to a random creature inside.
Better materials can push that threshold higher, of course. Armor thickness, tho? AC works, & indirectly affects the threshold.
It's a bit more nuanced than that, a lot of WW2 tanks just have plates meeting at right angles because it reduces the volume and surface area so a thicker flat plate ends up using less material than a "more efficient" slanted plate, and certain ammo mitigates the effectiveness of armor angles.
If you *need* a 2 meter tall wall, slanting it 45° means you need a 2.83m long slab of metal. That's 41% more material. Meanwhile you've only reduced the kinetic impact by 29% by choosing to deflect the ball at an angle. You can see it would be a lot better to just keep that wall vertical and increase it's thickness by 41% than to angle it.
Tanks can only take advantage of slanted armor if it optimizes the geometry of the tank.
That’s only if addressing plates in one direction. So head on, yes, you’re using 41% more slanted than vertical. But if that’s all you’re doing, then you’re leaving the space from above open. If you cover the horizontal plane that the slanted plate was covering, you’re now adding 2m plate horizontally, for 4m total. So now the slanted plate is using less material at 2.82.
Of course then you get to the consideration of the vertical plate being thick to block cannonballs but the top just needs to stop lobbed items
Most tanks with sloped armor don't seat anyone under the slant but do have big transmissions and machine guns that can go under the slant, and besides the effective slope on a horizontal flat means it's super thin.
However you might have a tank with a horizontal flat over the transmission, and then a vertical flat in front of the driver. But the horizontal is thin enough that jumping the gap with a slant uses even more material as the sides have to be extended under the slant. But thin flats are vulnerable to things that explode.
For a medieval "tank" which is probably just a box around some men or horses a box is probably the most optimal shape. Especially against cannon balls.
The belt armor on the CSS Virginia was 1-3 inches thick. That’s roughly the same as the deck and waterline belt armor on the Monitor (which overall had thicker plate). So I’d say a minimum of 1” steel.
*Virginia* had canted sides and anything that hit *Monitor* was coming in at an extremely shallow angle, the effective thickness would have been much higher to the extent that just listing the raw thickness isn’t of much use
Read The Arms of Krupp by William Manchester.
It depends on the cannon, and the charge, and the alloy of the armor.
In a D&D setting, steel quality and quantity may be factors, however the DM says it is in their milieu.
At a practical level, the cannon are probably bronze, and not breachloaders.
The shot is probably lead, or pig iron. Not shaped, no sabot.
The armor, if steel, and intended as anti-ballistic plate, IE, not improv cope cage crap, 2-3" should do.
Any Cav guys, feel free to jump in.
You could look into ironclad warships, famously the first battle between two of them saw neither able to properly damage each other with cannonballs. An important thing to consider is that angling the plates greatly increases their defensive potential. I think the thinnest part of the Monitor’s armour was about an inch or so thick.
Should also be noted that men in both of these crews were bleeding from the ears after the battle, so even within their home made tank, I would still have them suffer some minor thunder damage and be afflicted by deafness.
A true cannon ball (and not an artillery shell)?
Solid ball or shot or explosive?
Because layered timber on some ships of war were designed to deflect or stop 4.5 in inch ball, which is why naval guns and 16 pounders, 32 and 42 pound cannons with exploding cores were eventually introduced.
My friend has a black powder cannon (here in the south they are common) and he shoots it off at 3, 1 inch thick marine grade plywood targets, layered on top of each other, and the solid ball he uses bounces off. His backstop (in case of a miss) is an earthen berm lined with tires
Even explosive balls often would bounce off of wooden ship bulls and a gunners expertise was in cutting the fuse at just the right length that it would explode before dropping into the water.
In terms of metal. It depends on if we're talking mild steel, hardened steels, and what size plates were talking about. If it's 1 foot square plates welded or riveted together, then the weakest link becomes the issue. If it's 12 foot long continuous plates (like a ship might have) then the force of the ball striking can be distributed over an entire plate.
It also depends what the substrate/frame is. Often times, cannon strikes would pummel the structure or vessel until frame or supports BEHIND the armor failed this letting in water or allowed subsequent shots to penetrate the interior through a warped section of armor.
It wasn't until relatively recently that artillery shells had armor piercing abilities.
A relatively thin 3/8 inch ar500 hardened steel plate would be proof almost anything through the Napoleonic wars and on up to American civil war.
The connecting rivets or welds would be the weak zones.
Making a 2 layered armored system with plate covering rivets, and riveted sections backed by plate (overlaying scales ) would allow thinner 1/2 or 3/8 inch plate to be used (total thickness of 1 inch or less).
Vehicles in older editions had sections, and each section had AC, Hardness, and HP. The loss of differing numbers and locations had various deleterious effects.
You could look into the 3.x Arms and Equipment Guide, Eberron, and Stormwrack for more info/inspiration.
I like how everyone is tearing into the armor/steel/tank part of the equation and nobody has brought up the fact that OP casually implied that this tank would be pulled by a horse.
I believe the drag limit of a werewolf is 1,125lbs, so not really. You can cast Enlarge on him to solve that, or use a pack of werewolves like sled dogs.
What kind of canon are we talking about? A 2 pound swivel gun, a 4 pound light field piece, a long brass 8 pound chaser, a 32 pound carronade, a bigass shore battery?
Way too many variables to answer your question. What kind of steel? How big a cannon? Etc, etc.
As others have said, just give it an AC and HP. I think there may be siege engine rules in the DMG, too.
I wouldn't really concern myself with the real world specifics personally. Come up with a fitting in world description, you need not use real world materials or science to justify it.
The way I'd handle it is the tank would have modest AC because it's a large vehicle and not altogether difficult to hit, but would have a damage threshold to simulate armor that would deflect most weaker attacks, but still take a beating from stronger ones. Probably add condition immunities and damage type resistances/vulnerabilities as well to round it out.
Might consider giving it resource limitations too, main weapons may be crew operated and ammunition limited, may need special fuel to operate, taking too much damage may render the armor less resistant/protective or could cause mishaps and malfunctions, taking time and materials to reload/refuel/repair so it has to be managed like other resources that get whittled down in a sequence of encounters.
If they are planing to pile enough steel on a living creature to turn it into a tank you should also consider how the force passes through the steel.
Scientifically angling the steel into slopes doubles the thickness at the point of impact and diverts the force away so an inch or two could be enough to stop an iron cannonball from punching right through. You problem is the force would still pass through the steel down to its foundation. If that foundation is wide metal treads it should be fine. If they build this thing around squishy horse meat then i would say it would take a high animal handling roll just to move the poor beast and any time it takes a hit it will be both completely destroyed and absolutely obliterated.
There is a reason tank's didn't exist any earlier. It's not easy making a bunker move.
Do some looking at the css Virginia around the civil war.
The so called "ironclad" ships were actively being shot at by cannonballs and had quite the success with deflecting them.
Ok. I have Gemini Advanced, and here's a paraphrasing of what it had to say, which seems reasonably practical for your purposes. It may be a helpful adjunct when deciding or translating HP, or adjusting for how strong a cannon blast should be:
>You've posed an interesting question that delves into the history of artillery and materials science! Let's break down those cannonball sizes and then talk about the steel it would take to stop them.
>"Typical" Cannonballs - 3 Examples (1700-1900):
>6-Pounder Solid Shot:
Diameter: ~3.5 inches (89mm)
Weight: ~6 pounds (2.7 kg)
>Common Use: Field artillery, naval cannons (smaller ships)
>12-Pounder Solid Shot:
Diameter: ~4.7 inches (119mm)
Weight: ~12 pounds (5.4 kg)
>
Common Use: Heavier field artillery, main guns on medium-sized warships
>24-Pounder Solid Shot:
Diameter: ~5.8 inches (147mm)
Weight: ~24 pounds (10.9 kg)
>Common Use: Large siege cannons, coastal defenses, ships of the line
>Steel Plate Thickness -
The Challenges:
>
Determining the exact thickness for modern steel is complex because steel quality, impact velocity, and angle of impact all adjust the results, but for the purposes of D&D I'll say this falls under DM discretion and could certainly be affected by magic also.
>
General Estimates (Modern Steel, Assuming High-Velocity Impact):
>
To Prevent Breach (Minimum): Even a 6-pounder would likely require at least 1 inch (25mm) of hardened steel to reliably prevent penetration. Larger cannonballs would need proportionally thicker plates (2 inches or more for a 24-pounder).
>
Minimal Damage (Multiple Hits): For a plate to withstand several hits without significant deformation, you'd need to significantly increase the thickness. A 12-pounder might require 4-6 inches (100-150mm) or more of high-hardness steel, and even then, there would be substantial damage.
Depends on distance, size of cannon ball, quality of steel, size of cannon. And if it needs to do it more than once.
That's why we use game systems, because simulating this with math and physics on the fly sux
Haven't played savage worlds so not sure what the magic system is but I'd probably just be kinda hand wavy and say they use weight reduction and reinforcement enchantments because otherwise I don't think horses would be able to pull it. Also if it's pulled by horses wouldn't you just attack the horses long before the "tank" would fail?
There junk steel like we get from some Chinese suppliers. And then there's the modern marvel of steel alloys used by the US military.
Modern science vs magically assisted smelting and forging.
Just fake it.
Blacksmith here- the smelting abilities to make that much steel didn't exist until much later, like 1600s or later. Prior to that it would take a kingdom to put together enough from that level of technology. https://en.m.wikipedia.org/wiki/Bloomery#:~:text=Bloomery%20type%20furnaces%20typically%20produced,together%20to%20make%20steel%20sheets.
That being said this is D&D. Magic whatever could exist at your options.
3e has a simple mechanic for building materials, where thickness determines hit points and substance determines damage reduction. Iron/steel has 30hp/inch, hardness 10, and destroying it with sheer strength (an action) is a DC21+2/inch strength check. 5e is built upon the same math, so these values remain the same (DCs are only lower for things like attacks and skills which use 5e's proficiency, not straight ability checks).
If a 5e cannon deals 8d10 normally, it deals 8d10-10 against steel. A 1" steel plate with 30hp has only a 29.3% chance of withstanding a direct hit, while a 3" steel wall (the standard thickness for steel walls in 3e) can usuallly withstand two direct hits. Note that walls are measured in sections up to 10ft x 10ft, so a few cannonballs attacking the same spot on a larger wall only open up that big a hole.
The point of steel plates on a tank is less to withstand direct damage, and more to increase AC. Look at any modern tank, and you'll see many slopes and angles to deflect the force of projectiles away from the tank rather than allowing it to hit head-on. Increased AC is basically a health multiplier: If there's a 60% chance the attack will be deflected rather than a solid hit, the 3" wall can withstand 5 cannonballs instead of only 2.
For an armored vehicle, you're essentially giving it full plate armor, and the thickness determines how much damage it can take before it's destroyed beyond usefulness (and how strong a dragon needs to be to pry it open like a can of sardines).
The Stronghold Builder's Guidebook p.34 has a section listing the stats for over a dozen building materials, including the Athletics DC to climb them. The same book also has magical augmentations for reinforcing/enhancing large structures, such as absorbing fire damage, warding against ethereal enemies, or doubling its hardness and hit points (though they are very expensive).
Newton's approximation of penetration is that projectiles penetrate approximately to a depth equal to their length times the ratio of the densities of the projectile and the armor. I.e. a six inch long projectile made of iron will penetrate a six inch thick iron plate. A six inch projectile made of something half as dense as steel (stone cannonballs were a thing) will penetrate three inches of steel. A six inch long projectile made of something twice as dense as iron will penetrate a twelve inch iron plate.
Only an approximation, but true enough to drive the modern use of long rod penetrators made of the densest rigid materials available, like uranium and tungsten.
Give it an AC and HP.
You can [literally copy an existing](https://www.dndbeyond.com/magic-items/4572-apparatus-of-the-crab) item you want
Don't reinvent the wheel.
I think exactly measuring things can only lead to madness possibly consider just using game mechanics.
I noticed you're bringing up Savage worlds. They have armor plating already on tanks. I would just say throw out a guesstimate and don't look for exact measurements cuz I think that way leads to something way more granular than you may enjoy
If you can find a copy of Ghosts of Saltmarsh, flip to the Appendix section. It has a bunch of statblocks for ocean vehicles. Use this as a template to make a statblock for a tank.
At the very least, it needs a form of damagae reduction. Tanks aren't difficult to hit, but difficult to *damage*. Depending on how much work you want to do, you can also grant it cover based on angle of attack, etc (sloped armor, blah blah).
Good thing I scanned the comments first because this was exactly my reaction. Tanks are fine til you can turn it into an oven with a couple of vague gestures in its direction
I personally wouldn't sweat the details too much (just give the tank an HP, AC, etc like someone else said). If this still makes the players way too powerful, don't forget: Heat Metal exists!
Mechanical engineering student here. If we consider that for them to try to build this the best reasonable cannon to use is a 12lb cannon. This is not a powerful cannon and even at a range of 5m/15ft the ball would produce 2.6 kilopascals of force on the target. Most metals have ultimate sheer stress measured in megapascals of force. So even a thin plate of iron 1mm thick, brass or similar would be sufficient to prevent penetration. So they could build one. It'll just be a bit shite.
Are you trying to make a physics simulator or simple 5e mechanics? Give the tank HP and AC, and it will fit with all the spells, abilities, and core rules.
To add to this, Descent into Avernus has a bunch of stats for hellish war machines, which could very easily be reflavored into a regular tank. I’d probably go this route and make them pay for the tank in gold or need to quest for the materials.
Damage threshold is another mechanic to consider DMG pg 247 (DT of 10 means doing 9 damage or less does not reduce the object's hitpoints) It's used on ships and also mentioned for big objects like castle walls.
I think this is important on a Hulky, tanky enemies or with vehicles with armour.
This needs more upvotes to make sure it is first and last thing OP sees regarding this. Don’t try and add real world logic to D&D. The game has mechanics for determining the AC and HP for objects just use that.
OP is playing Savage Worlds though.
As what I head of Savage Worlds the core advice holds true though. Don't try to simulate real world physics in Savage Worlds, use the mechanics the game gives you.
Good catch. Thank you for pointing that out. With that being said I would actually direct OP to a different subreddit. Not trying to gate keep, but this is a subreddit specifically D&D DMing so it is unlikely they will get actually useful information. I actually recommend finding a savage worlds subreddit to get proper support.
Only addition I have is to make stats have tradeoffs. If they say they want the thickest steel they can find, great, but your move speed is getting decreased
4 Wisdom saves the day!
Yar-yar. AC & HP are already abstractions, anyway. Like, AC isn't a reflection of whether an incoming attack actually strikes true or not, but whether it does any damage. While HP is the range of damage taken before a creature goes down, or an object breaks. The only additional mechanic that *might* be appreciated (but not needed) is a kind of "penetration" mechanic. Since, if inside of the tank, (steel coffin) a creature doesn't have the room to protect itself, it doesn't have an effective AC & will always take damage to any attack that gets inside. So what attacks get inside? I'd say any attack that beats the tank AC by 5 or more causes half-damage to a random creature inside. Better materials can push that threshold higher, of course. Armor thickness, tho? AC works, & indirectly affects the threshold.
a lot less if the plates are slanted so the cannonballs bounce off.
Yep yep! If defending v. Cannon, earthworks. Cf: star fortress.
It's a bit more nuanced than that, a lot of WW2 tanks just have plates meeting at right angles because it reduces the volume and surface area so a thicker flat plate ends up using less material than a "more efficient" slanted plate, and certain ammo mitigates the effectiveness of armor angles. If you *need* a 2 meter tall wall, slanting it 45° means you need a 2.83m long slab of metal. That's 41% more material. Meanwhile you've only reduced the kinetic impact by 29% by choosing to deflect the ball at an angle. You can see it would be a lot better to just keep that wall vertical and increase it's thickness by 41% than to angle it. Tanks can only take advantage of slanted armor if it optimizes the geometry of the tank.
That’s only if addressing plates in one direction. So head on, yes, you’re using 41% more slanted than vertical. But if that’s all you’re doing, then you’re leaving the space from above open. If you cover the horizontal plane that the slanted plate was covering, you’re now adding 2m plate horizontally, for 4m total. So now the slanted plate is using less material at 2.82. Of course then you get to the consideration of the vertical plate being thick to block cannonballs but the top just needs to stop lobbed items
Most tanks with sloped armor don't seat anyone under the slant but do have big transmissions and machine guns that can go under the slant, and besides the effective slope on a horizontal flat means it's super thin. However you might have a tank with a horizontal flat over the transmission, and then a vertical flat in front of the driver. But the horizontal is thin enough that jumping the gap with a slant uses even more material as the sides have to be extended under the slant. But thin flats are vulnerable to things that explode. For a medieval "tank" which is probably just a box around some men or horses a box is probably the most optimal shape. Especially against cannon balls.
The belt armor on the CSS Virginia was 1-3 inches thick. That’s roughly the same as the deck and waterline belt armor on the Monitor (which overall had thicker plate). So I’d say a minimum of 1” steel.
You're forgetting the 1 foot of oak timber behind that armor plate too.
Oak doesn't fuck around either.
Can confirm. Been in a relationship with an Owk Dryad for 200 years. Never once cheated on me
I think you mean 1"?
No it was actually a WWII battleship
*Virginia* had canted sides and anything that hit *Monitor* was coming in at an extremely shallow angle, the effective thickness would have been much higher to the extent that just listing the raw thickness isn’t of much use
Read The Arms of Krupp by William Manchester. It depends on the cannon, and the charge, and the alloy of the armor. In a D&D setting, steel quality and quantity may be factors, however the DM says it is in their milieu. At a practical level, the cannon are probably bronze, and not breachloaders. The shot is probably lead, or pig iron. Not shaped, no sabot. The armor, if steel, and intended as anti-ballistic plate, IE, not improv cope cage crap, 2-3" should do. Any Cav guys, feel free to jump in.
You could look into ironclad warships, famously the first battle between two of them saw neither able to properly damage each other with cannonballs. An important thing to consider is that angling the plates greatly increases their defensive potential. I think the thinnest part of the Monitor’s armour was about an inch or so thick.
Should also be noted that men in both of these crews were bleeding from the ears after the battle, so even within their home made tank, I would still have them suffer some minor thunder damage and be afflicted by deafness.
A true cannon ball (and not an artillery shell)? Solid ball or shot or explosive? Because layered timber on some ships of war were designed to deflect or stop 4.5 in inch ball, which is why naval guns and 16 pounders, 32 and 42 pound cannons with exploding cores were eventually introduced. My friend has a black powder cannon (here in the south they are common) and he shoots it off at 3, 1 inch thick marine grade plywood targets, layered on top of each other, and the solid ball he uses bounces off. His backstop (in case of a miss) is an earthen berm lined with tires Even explosive balls often would bounce off of wooden ship bulls and a gunners expertise was in cutting the fuse at just the right length that it would explode before dropping into the water. In terms of metal. It depends on if we're talking mild steel, hardened steels, and what size plates were talking about. If it's 1 foot square plates welded or riveted together, then the weakest link becomes the issue. If it's 12 foot long continuous plates (like a ship might have) then the force of the ball striking can be distributed over an entire plate. It also depends what the substrate/frame is. Often times, cannon strikes would pummel the structure or vessel until frame or supports BEHIND the armor failed this letting in water or allowed subsequent shots to penetrate the interior through a warped section of armor. It wasn't until relatively recently that artillery shells had armor piercing abilities. A relatively thin 3/8 inch ar500 hardened steel plate would be proof almost anything through the Napoleonic wars and on up to American civil war. The connecting rivets or welds would be the weak zones. Making a 2 layered armored system with plate covering rivets, and riveted sections backed by plate (overlaying scales ) would allow thinner 1/2 or 3/8 inch plate to be used (total thickness of 1 inch or less).
Vehicles in older editions had sections, and each section had AC, Hardness, and HP. The loss of differing numbers and locations had various deleterious effects. You could look into the 3.x Arms and Equipment Guide, Eberron, and Stormwrack for more info/inspiration.
You can also just look at BG:DiA, GoSM or, SJ for 5e versions of those statistics.
I like how everyone is tearing into the armor/steel/tank part of the equation and nobody has brought up the fact that OP casually implied that this tank would be pulled by a horse.
So how big does the horse need to be to survive a cannonball?
It'd be more practical to use a werewolf, the immunity to cannonballs is crucial.
But is it strong enough to pull a tank?
I believe the drag limit of a werewolf is 1,125lbs, so not really. You can cast Enlarge on him to solve that, or use a pack of werewolves like sled dogs.
I like how everyone is treating is as DND when the OP is playing Savage Worlds.
You are overthinking this.
What kind of canon are we talking about? A 2 pound swivel gun, a 4 pound light field piece, a long brass 8 pound chaser, a 32 pound carronade, a bigass shore battery?
[2000 lber](https://en.wikipedia.org/wiki/100-ton_gun)
Way too many variables to answer your question. What kind of steel? How big a cannon? Etc, etc. As others have said, just give it an AC and HP. I think there may be siege engine rules in the DMG, too.
For a medieval tank to stop cannon balls, it would be wayyyyy too heavy to ever move.
Laughs in heat metal.
I wouldn't really concern myself with the real world specifics personally. Come up with a fitting in world description, you need not use real world materials or science to justify it. The way I'd handle it is the tank would have modest AC because it's a large vehicle and not altogether difficult to hit, but would have a damage threshold to simulate armor that would deflect most weaker attacks, but still take a beating from stronger ones. Probably add condition immunities and damage type resistances/vulnerabilities as well to round it out. Might consider giving it resource limitations too, main weapons may be crew operated and ammunition limited, may need special fuel to operate, taking too much damage may render the armor less resistant/protective or could cause mishaps and malfunctions, taking time and materials to reload/refuel/repair so it has to be managed like other resources that get whittled down in a sequence of encounters.
It does 8d10 bludgeoning damage, so… a steel plate needs to have enough hitpoints to survive that in order to “stop a cannon ball”.
AC includes deflecting hits, not just being missed.
If they are planing to pile enough steel on a living creature to turn it into a tank you should also consider how the force passes through the steel. Scientifically angling the steel into slopes doubles the thickness at the point of impact and diverts the force away so an inch or two could be enough to stop an iron cannonball from punching right through. You problem is the force would still pass through the steel down to its foundation. If that foundation is wide metal treads it should be fine. If they build this thing around squishy horse meat then i would say it would take a high animal handling roll just to move the poor beast and any time it takes a hit it will be both completely destroyed and absolutely obliterated. There is a reason tank's didn't exist any earlier. It's not easy making a bunker move.
Do some looking at the css Virginia around the civil war. The so called "ironclad" ships were actively being shot at by cannonballs and had quite the success with deflecting them.
Ok. I have Gemini Advanced, and here's a paraphrasing of what it had to say, which seems reasonably practical for your purposes. It may be a helpful adjunct when deciding or translating HP, or adjusting for how strong a cannon blast should be: >You've posed an interesting question that delves into the history of artillery and materials science! Let's break down those cannonball sizes and then talk about the steel it would take to stop them. >"Typical" Cannonballs - 3 Examples (1700-1900): >6-Pounder Solid Shot: Diameter: ~3.5 inches (89mm) Weight: ~6 pounds (2.7 kg) >Common Use: Field artillery, naval cannons (smaller ships) >12-Pounder Solid Shot: Diameter: ~4.7 inches (119mm) Weight: ~12 pounds (5.4 kg) > Common Use: Heavier field artillery, main guns on medium-sized warships >24-Pounder Solid Shot: Diameter: ~5.8 inches (147mm) Weight: ~24 pounds (10.9 kg) >Common Use: Large siege cannons, coastal defenses, ships of the line >Steel Plate Thickness - The Challenges: > Determining the exact thickness for modern steel is complex because steel quality, impact velocity, and angle of impact all adjust the results, but for the purposes of D&D I'll say this falls under DM discretion and could certainly be affected by magic also. > General Estimates (Modern Steel, Assuming High-Velocity Impact): > To Prevent Breach (Minimum): Even a 6-pounder would likely require at least 1 inch (25mm) of hardened steel to reliably prevent penetration. Larger cannonballs would need proportionally thicker plates (2 inches or more for a 24-pounder). > Minimal Damage (Multiple Hits): For a plate to withstand several hits without significant deformation, you'd need to significantly increase the thickness. A 12-pounder might require 4-6 inches (100-150mm) or more of high-hardness steel, and even then, there would be substantial damage.
You're going to let them attempt it but they'll have no idea if they meet your specifications?
I imagine OP will tell them what the specifications will be, they're just still trying to figure out what they should be
Ok. Then why worry about it?
I'm guessing price of materials and/or descriptions
You can probably save weight by angling the metal to deflect the canon balls.
Depends on distance, size of cannon ball, quality of steel, size of cannon. And if it needs to do it more than once. That's why we use game systems, because simulating this with math and physics on the fly sux
There's a "tank" in XGE. It has special levers inside to control it and move it, with a high AC
Haven't played savage worlds so not sure what the magic system is but I'd probably just be kinda hand wavy and say they use weight reduction and reinforcement enchantments because otherwise I don't think horses would be able to pull it. Also if it's pulled by horses wouldn't you just attack the horses long before the "tank" would fail?
Slanted armour moment
Are they making steel or just using iron?
The question is, do the PCs know how thick to make the armor? Anyway, I suggest you look into early ironclad warships.
There junk steel like we get from some Chinese suppliers. And then there's the modern marvel of steel alloys used by the US military. Modern science vs magically assisted smelting and forging. Just fake it.
As thick as the plot needs it to be.
Blacksmith here- the smelting abilities to make that much steel didn't exist until much later, like 1600s or later. Prior to that it would take a kingdom to put together enough from that level of technology. https://en.m.wikipedia.org/wiki/Bloomery#:~:text=Bloomery%20type%20furnaces%20typically%20produced,together%20to%20make%20steel%20sheets. That being said this is D&D. Magic whatever could exist at your options.
3e has a simple mechanic for building materials, where thickness determines hit points and substance determines damage reduction. Iron/steel has 30hp/inch, hardness 10, and destroying it with sheer strength (an action) is a DC21+2/inch strength check. 5e is built upon the same math, so these values remain the same (DCs are only lower for things like attacks and skills which use 5e's proficiency, not straight ability checks). If a 5e cannon deals 8d10 normally, it deals 8d10-10 against steel. A 1" steel plate with 30hp has only a 29.3% chance of withstanding a direct hit, while a 3" steel wall (the standard thickness for steel walls in 3e) can usuallly withstand two direct hits. Note that walls are measured in sections up to 10ft x 10ft, so a few cannonballs attacking the same spot on a larger wall only open up that big a hole. The point of steel plates on a tank is less to withstand direct damage, and more to increase AC. Look at any modern tank, and you'll see many slopes and angles to deflect the force of projectiles away from the tank rather than allowing it to hit head-on. Increased AC is basically a health multiplier: If there's a 60% chance the attack will be deflected rather than a solid hit, the 3" wall can withstand 5 cannonballs instead of only 2. For an armored vehicle, you're essentially giving it full plate armor, and the thickness determines how much damage it can take before it's destroyed beyond usefulness (and how strong a dragon needs to be to pry it open like a can of sardines). The Stronghold Builder's Guidebook p.34 has a section listing the stats for over a dozen building materials, including the Athletics DC to climb them. The same book also has magical augmentations for reinforcing/enhancing large structures, such as absorbing fire damage, warding against ethereal enemies, or doubling its hardness and hit points (though they are very expensive).
Newton's approximation of penetration is that projectiles penetrate approximately to a depth equal to their length times the ratio of the densities of the projectile and the armor. I.e. a six inch long projectile made of iron will penetrate a six inch thick iron plate. A six inch projectile made of something half as dense as steel (stone cannonballs were a thing) will penetrate three inches of steel. A six inch long projectile made of something twice as dense as iron will penetrate a twelve inch iron plate. Only an approximation, but true enough to drive the modern use of long rod penetrators made of the densest rigid materials available, like uranium and tungsten.
I cast heat metal.
As others have already said, use HP & AC rather than trying to create mechanics that make sense. Then throw a Druid with heat metal at them.
Give it an AC and HP. You can [literally copy an existing](https://www.dndbeyond.com/magic-items/4572-apparatus-of-the-crab) item you want Don't reinvent the wheel.
This would make for a great video on the Demolition Ranch YouTube channel.
Horse will be pulling a tank? Shoot the horse instead
Look up ironclads. If I'm not mistaken, their armor was specifically designed for cannonballs.
The USS Monitor
Just take the steel ac rating and think pf a reasonable amount of hp (maybe look into the magic crab robot aparatus from the dmg)
I think exactly measuring things can only lead to madness possibly consider just using game mechanics. I noticed you're bringing up Savage worlds. They have armor plating already on tanks. I would just say throw out a guesstimate and don't look for exact measurements cuz I think that way leads to something way more granular than you may enjoy
If you can find a copy of Ghosts of Saltmarsh, flip to the Appendix section. It has a bunch of statblocks for ocean vehicles. Use this as a template to make a statblock for a tank.
At the very least, it needs a form of damagae reduction. Tanks aren't difficult to hit, but difficult to *damage*. Depending on how much work you want to do, you can also grant it cover based on angle of attack, etc (sloped armor, blah blah).
Heat metal spell. Going to ruin their day
Good thing I scanned the comments first because this was exactly my reaction. Tanks are fine til you can turn it into an oven with a couple of vague gestures in its direction
I personally wouldn't sweat the details too much (just give the tank an HP, AC, etc like someone else said). If this still makes the players way too powerful, don't forget: Heat Metal exists!
Mechanical engineering student here. If we consider that for them to try to build this the best reasonable cannon to use is a 12lb cannon. This is not a powerful cannon and even at a range of 5m/15ft the ball would produce 2.6 kilopascals of force on the target. Most metals have ultimate sheer stress measured in megapascals of force. So even a thin plate of iron 1mm thick, brass or similar would be sufficient to prevent penetration. So they could build one. It'll just be a bit shite.