# Are “Bomb Catapults” actually feasible?

I was recently thinking about which technologies an Isekai-Protagonist could give his allies in a medival fantasy world. For all those who don't know, Isekai is an anime genre where the protagonist is a real world human who get transported into a fantasy world. Come to think of it, this question applies to time travelers as well.

Assume that I've joined a local lord after I established my value and that I'm a respected advisor. Since he is at war with the good guy empire, I decided to help the war effort by introducing gun powder to this world. I don't know the exact formula, but I know that I need charcoal, sulfur and salpeter. With the might of the scientific method and the more or less voluntary help of laboratory slaves I'll figure it out.

However I'm uncertain which application of gunpowder I should pitch to the Dark Khan. Sure, splinter granades are a no-brainer, but I feel that I can do better. While I'm certain that I could teach the artisans the Overlord bound in this service conquering far away lands how to make guns and cadnnons eventually, I want to show results quickly.

The basic idea is to build large splinter bombs to devastate the enemy heavy infantry. Horse archers, shock cavalry and auxiliaries will do the rest. I want to use catapults to launch the bombs. Figuring out artillery maths was one of my early projects, so accuracy shouldn't be an issue.

I got three projectile designs in mind. All are strong, waterproof sacks filled with an outer layer of gunpowder and shrapnel, an inner gunpowder core and a lute. The first design is as simple as that and could be made quickly. However I'm wondering if having the bomb explode above ground would be deal more damage. This would mean that I would have to work out the timing of the lute. Another, even more complex idea of mine was to attach a wodden pole with large fletchings. I hope that this would make it predictable which side would be down during the fall. This might allow me to improve the bombs inner structure to some sort of directional bomb. This would of cause require even more research to figure out. Which of these designs is best? Does the improvement of the bombs performance type 2 and 3 would bring really justify the extra effort? Or are my bomb catapults a bad idea all together and I should use the gun power in another way altogether to help the war effort?

Note that sieges aren't the issue, large field battles are. Our shamans got biological warfare down to the pont that most cities prefer to surrender.

• Which "lute" are you referring to? – Alexander Mar 2 '20 at 17:57
• Does "lute" mean "Fuse"? – Paul TIKI Mar 2 '20 at 18:02
• – Alexander Mar 2 '20 at 18:04
• @Alexander If you can "corn" the gunpowder (mix it wet, compress it into cakes, grind it up, and then sieve it into different "grades") then you can make more reliable fuses. The question then is whether OP's protagonist would think of or remember that... – Chronocidal Mar 3 '20 at 12:10

Gunpowder more of a low explosive rather than a high explosive -- it burns slowly compared to more modern explosives and is therefore much more effective as a propellent. This is exactly how it was first used in the early gunpowder era, to propel first rockets and then to fire cannonballs - first stone, then iron and lead projectiles.

Of course, you can make a bomb from gunpower, and many people still do-- the modern improvised 'pipe bomb' made from black powder is exactly this sort of weapon. It's just not very effective (luckily).

Arranging an airburst is possible, but extremely difficult: you need a fuse which will burn for exactly the right length of time to within a fraction of a second.

If you are set on explosive warheads rather than cannonballs or rockets, here's an alternative suggestion: cluster bombs! Instead of one large projectile, hurl dozens of small grenade-like bombs which will cover a wide area and cause far more infantry casualties than a unitary warhead. They will be less effective against fortifications, but that doesn't seem to be your requirement.

• Or an even easier alternative to cluster bombs would be grapeshot: basically artillery sized shotguns. – Nosajimiki Mar 2 '20 at 19:29
• How do we detonate cluster bomb units? – Alexander Mar 3 '20 at 1:41
• @Alexander Normal fuses should be fine, no need to be as precise as with a single large warhead. – user72778 Mar 3 '20 at 6:07
• @user-658537 how do you ignite them all at once? – Alexander Mar 3 '20 at 8:26
• @Alexander tie the fuses together and light the knot before launching. – zovits Mar 3 '20 at 8:57

Yes, but only to an extent

If the only thing that you have to play with is black gunpowder, you will get much more effect by developing artillery rather than "trebuchet shells".

Yes, we can have explosive shells filled with gunpowder. The biggest issue is how to timely set them off, and avoid your artillery team accidentally blowing itself up. Generally, you need a lot of trial and error to develop even somewhat reliable "slow fuse", and even then its reliability won't be very good.

Your design #1 "a sack with a fuse" will burst when it hits the ground. A natural fix is to switch to hard shells, like cast iron. This way you can have an effective bombardment.

Design #2 "short fuse" would endanger your own forces, because, as I said, you can't have reliable fuses, and you would have to set explosion time too short to be comfortable.

Design #3 "javelin bombs" might work, if javelin design is worked to perfection. However, the charge can't be big, because the javelin would not fly right, or either break or topple on landing.

Your trouble can be fixed in two ways:

1) Contact detonators. It won't be an airburst, but still much more effective than gunpowder fuses;

2) Clockwork fuses. Those are in fact reliable and actually used to produce an airburst attack.

Both of those fixes, unfortunately, would require XIX century level technology.

Meanwhile, good old cannons were effective very early in gunpowder era.

• Artillery is only worthwhile if you've got access to vast quantities of bronze. If you don't have that, your only options are catapults and gunpowder rockets (and remember, the rockets are going to be horribly inaccurate). – Mark Mar 3 '20 at 1:23
• @Mark bronze was indeed an early preferred metal to make cannons, but iron could be (and actually was) used as well. – Alexander Mar 3 '20 at 1:34
• Iron guns have a disturbing habit of shattering when fired, killing everyone around them. Bronze guns also fail, but they tend to do so less violently, only killing the people who actually get caught in the blast. – Mark Mar 3 '20 at 1:37
• "Yes, we can have explosive shells filled with gunpowder. The biggest issue is how to timely set them off" - this did exist historically, see howitzers and mortars. It was a great art back in the 17th century, to make shells and set fuses so they exploded right above the head of the enemy. When they got it right, it had a devastating effect on close formations. – vsz Mar 3 '20 at 5:16

Assuming for some reason that you cannot or will not be able to create cannons (and early cannons were made using the same process as casting bells, or using the skills of coopers to make "barrels" out of metal strips rather than wooden ones, so it is difficult to understand why you would not), then using some sort of catapult mechanism to fire fused projectiles makes sense.

Early bronze cannon, cast in the same manner as a bell

As many other posters have noted, the key issue is making reliable fuses. This problem persisted even into the late 19th century until reliable mechanical fuses were perfected, so the ability to make something like this is likely lacking in your environment. One issue which I don't think has been touched upon is the need for the fuse to stay lit while in flight. A simple piece of burning cloth, paper or cork is likely to go out under acceleration during the shot, or while flying through the air, leaving a live bomb in the hands of the enemy (who may know enough to either recover the gunpowder or shoot it back at you!). Early "Matchlock" firearms used a piece of cord soaked with potassium nitrate in order to ensure the match would burn reliably. One thing gunners would do was blow on the burning match to ensure the tip was hot enough to ignite the powder. The act of flying through the air should serve the same purpose, but once again, there will be variability (if the round rotates in flight, the match might be shielded from the airflow that keeps it hot).

Using a "javelin" type projectile can increase reliability and accuracy, but at the cost of needing a ballista to fire it. Ballista were "torsion" engines that used skeins of sinew or rope to provide the driving power, and were quite expensive and needed trained engineers to operate and maintain. However, ballista were quite powerful and accurate, so the ability to send a javelin or a bomb carrying javelin may be enough justification to develop and use these weapons.

Large ballista

The advantage of a ballista is you can shoot javelins several hundred meters, and switch over to "bombs" as the enemy closes the distance. A ballista can also shoot ordinary projectiles as well, so the crew can switch from explosives to ordinary javelins and rocks as the situation dictates. This also saves a great deal of expense, since explosive projectiles might be very expensive. Another advantage is if the projectiles are made carefully, the crew can fire ranging shots with non explosive projectiles and then fire the explosive one once the range to the enemy haas been established. This requires that all rounds have the same weight so the performance is known.

So there is no reason not to be able to use ballista as your mechanism to shoot explosive rounds, and a ballista will provide the performance and reliability needed to make this work.

• I believe it is not that they cannot make cannons, but OP mentioned he is looking for equipment for field battles rather than sieges, and cannons are not as useful there. – Junkrat Mar 3 '20 at 15:52
• Cannons were used in the field as far back as the 1400's, so that argument is a bit thin. It is true, however, that effective field artillery needed about 200 years to be developed - King Gustavus Adolphus of Sweden pioneered effective mobile field artillery in the 30 years war. – Thucydides Mar 4 '20 at 17:33

Well, once you figure out how to create the gunpowder, you are going to have to work on standardization.

The key to creating an effective Air burst type bomb is going to be the fuse. So you have to work the standard throughout the process. So lets start with the gunpowder. When you figure it out, make as certain as possible that the proportions are recorded and used EVERY time. Next, there is variation in charcoals from different types of wood. I once read an old treatise on creating gunpowder during the westward expansion in the US. The author stressed that you should only use charcoal from a Willow tree to make black powder as it burned faster. So if you find this to be true, record it and always use the same kind of charcoal. Same with the "Saltpetre" The treatise I read said something about creating raised straw beds to pee in out in the sun, and you could harvest the crystalline material left after the water evaporated. He also mentioned that sourcing it from seabird guano worked even better but may not be available. Find the best source and again, document. Same with the Sulfer. The point of all of this is that you want to go to a huge warehouse of gunpowder, pick a batch at random, and it will perform exactly the same as any other.

Next, your first fuses are going to be pretty much gunpowder rolled into paper. Again, standardize the process. For every 12 inch fuse, you use exactly 1 oz of gunpowder in paper of x and y dimensions, sourced from a factory that gives consistent results. Your goal, again, is to be able to take 25 fuses out of a huge batch and they all burn at exactly the same rate.

Now you blend your expertise in ballistics with the fuse timing. You know your fuse burn rate now, and you can calculate the time it will take a projectile to impact the ground. Cut your fuse to the length you need for the projectile to travel, subtracting a second or two of burn time. If it's a little short, it still explodes over the battle field. It may be a bit less effective than you'd like, but will still be scary as heck. If it goes long, the explosion after it hits will still cause a lot of problems. The ones that work right will be hugely effective.

This moves me along to building your shells in such a way that they are deadly to the enemy no matter what they do. Make them heavy, make them large. Even throwing large rocks from a trebuchet is effective against massed ranks of the enemy. If the big rock goes boom after it has crushed a bunch of infantry and maybe a horse or two, even better.

The idea of putting some sort of guidance pole on the back of a projectile isn't going to be helpful as far as the explosive part unless you have the means to create a proximity fuse.

So, If all of your Trebuchets are the same, and all of your Bombs are the same, and all of your fuses are the same, you should be able to set up reasonably reliable airiel bursts. Even if it doesn't work perfectly, you are still building a reliable weapon.

You are describing artillery, The King of the Battlefield. If you could make cannons, that would be better, but trebuchets throwing 150+ lbs explosives shells is a pretty good approximation and would be devastating against massed soldiery.

In general, airbursts are most effective against ground forces. The shrapnel -- splinters in your case -- rains down on the soldiery with its highest velocity and they don't have any cover except their armor and shields. Ground bursts throw dirt and debris up and out, but the ground itself can shield the targets from the explosion and shrapnel.

Contact explosions are good against structures and very heavily armored vehicles. You may not breach the walls or armor but the shockwaves along can kill humans on the other side.

There is another factor to your weapons that you didn't raise that is a powerful killing action. Create enough heat and combustion that you consume all the oxygen in the local area and leave heavy gases -- particulates, $$CO_2$$, $$NO_x$$, $$SO_x$$ -- in their place so your targets either have to run for their lives -- breaking cover -- or suffocate. This is one lethal mechanism of Fuel Air Bombs like the MOAB. Obviously, anything like a MOAB can't be delivered by catapult. The topic is raised to identify an additional measure of lethality.

• @Alexander, I double checked my assertions, and you're right. I was off by a factor of 5 or so. Thanks – EDL Mar 2 '20 at 19:22
• Do you have a proposal for getting air burst to work with medieval technology? – user72778 Mar 3 '20 at 6:11
• The OP seems to have a proposal already. They refer to use a lute as a triggering mechanism. Otherwise a fuse or acid-wax system should work to a few 10 of msecs. – EDL Mar 3 '20 at 7:02
• @user-658537 : they did have airburst with medieval technology, with a carefully measured length of fuse. Of course, it didn't always work, but they didn't fire just a single shot. It took a lot of practice, it was almost a form of art (or just luck) to get it right. – vsz Mar 3 '20 at 8:10