The Eldritch Knight Cannon Trick
The idea behind this has lived in green texts and forum threads for a while.
- Play Fighter (Eldritch Knight) 3.
- Perform the weapon bond ritual with a Cannon (or any siege weapon that can be fired by one person).
- Load the Siege Weapon.
Now you have a fully loaded Cannon that you can teleport to you with a bonus action, and fire at a +6 for 8d10 bludgeoning damage.
RAW Interpretations
First lets talk about weapon bond.
Weapon Bond
At 3rd level, you learn a ritual that creates a magical bond between yourself and one weapon. You perform the ritual over the course of 1 hour, which can be done during a short rest. The weapon must be within your reach throughout the ritual, at the conclusion of which you touch the weapon and forge the bond.
So we need to spend an hour within reach of a weapon, touch it at the end and it’s bonded.
“Aha! I’ve got you” says the rules lawyer, “Siege weapons are typed as Large Objects in the DMG, therefore they are not weapons.”.
If only the quality of D&D’s rules text was enough, unfortunately large object is still extremely ambiguous in terms of rules since all weapons are objects (in fact everything that’s not a creature, point in space, vehicle or structure is an object) and absence of evidence is not evidence of absence.
Once you have bonded a weapon to yourself, you can’t be disarmed of that weapon unless you are incapacitated. If it is on the same plane of existence, you can summon that weapon as a bonus action on your turn, causing it to teleport instantly to your hand.
This however is a much bigger dampener on things, “causing it to teleport instantly to your hand” heavily implies that the intent is for the use of at least man-portable weapons and pushes us into the realm of GM caveat. But you’re a grown up, you already knew that the answer to all of this was “Ask your GM if this is okay.”.
You can have up to two bonded weapons, but can summon only one at a time with your bonus action. If you attempt to bond with a third weapon, you must break the bond with one of the other two.
Now we get into something very spicy. The oft overlooked clause that says “oh no, it’s not just one Cannon… It’s two.”
Cannon
Large object
Armor Class: 19
Hit Points: 75
Damage Immunities: poison, psychic
Damn this thing is a tank. AC 19 and 75 HP is nothing to sniff at, even if it doesn’t go off you can still use the threat of it to soak enemy attacks.
A cannon uses gunpowder to propel heavy balls of cast iron through the air at destructive speeds. In a campaign without gunpowder, a cannon might be an arcane device built by clever gnomes or wizardly engineers.
A cannon is usually supported in a wooden frame with wheels. Before it can be fired, the cannon must be loaded and aimed. It takes one action to load the weapon, one action to aim it, and one action to fire it.
Now this is a tricky one, we’ll say that you’ve loaded it already, but it’s probably too much of a stretch to say you could have pre-aimed it unless you’re just setting it level and summoning it straight in front of you (and even then I’d probably rule that it was attacking with disadvantage). So you’re going to need two actions to do this, luckily you’re playing a Fighter already so you can action surge!
Cannon Ball. Ranged Weapon Attack: +6 to hit, range 600/2,400 ft., one target. Hit: 44 (8d10) bludgeoning damage.
Ah, well that’s not as shiny as we were hoping was it. Well let’s break this down, take an Owl Bear for instance, a pretty reasonable enemy for a level 3 Eldritch Knight. It has an AC of 13, so hit it 70% of the time. Oh, well at least that’s a slightly better rate than 5e’s standard 65%. Well let’s say we hit it, we’re doing 8d10 damage and it has 59 hp, so we can one shot it a whopping 3.69% of the time! Oh. Well maybe it’s action efficient!
We took two actions and a bonus action for a 70% chance at an average of 44 damage. Giving us an expected damage of 30.8.
What about our sharpshooter fighter friend. They only hit 55% of the time because of Sharpshooter, but they’ll do an average of 18.5 damage each time. So they only do 20.35 damage! Until the next level when they get crossbow expert and can use their bonus action too, jumping to to 28.9 damage.
This is the best the Cannon Trick’s math is ever going to be, as you get towards level 5 and above the static +6 is really going to hurt it’s ability to hit.
Optimizing
So you showed your GM the first half of this explaining that it’s not actually a scary amount of damage on a one off (read high variance) strategy that requires a lot of action economy investment as well as fun RP potential of your characters trying to get hold of a cannon.
Now let’s break it in half.
Class Features
Fighting Style Archery is really the only thing that jumps out at me and even then since the cannon has a Static +6 it probably doesn’t stack. War magic doesn’t really help us with our action economy on our Cannon turn, and Arcane Charge is nice for positioning but doesn’t help outside of maybe getting us advantage from height which is a little too situational.
Feats
- Eldritch Adept Devilsight darkness combo comes online once you get 2nd level spells at level 7.
- Elven Accuracy is cracked in half, it is the reason to play elves over custom origin. If you have a reliable way to gain advantage then this opens the door to not just making the cannon trick reliable, but also letting you crit fish with it.
- Gunner is a bit of a stretch, once again it will live of die on GM caveat. Firing a cannon in melee is extremely cool, and we would love to be able auto load the cannon.
- Sharpshooter while we don’t need the damage as much, not taking the long range penalty sets up some pretty absurd nonsense, take fights from 2,400 ft away, get your team to help out with reloading, and put shots down range until they catch up with you. Your GM will probably allow you to do this once before they learn an important lesson about line of sight.
Spells
1st Level Spells
First level spells give us access to Find Familiar, we can get them to take the help action to give us advantage on every cannon shot, which will keep it relevant against higher ACs and massively reduce the risk of us spending all those actions doing nothing.
Our alternative for Advantage farming is Silvery Barbs, which is also just an extremely good spell all round, but it’s probably better left to folks who have enough spell slots to use it more frequently.
Unseen servant is a strong maybe, a lot of it depends on if aiming or firing a cannon is a “simple task that a human servant could do”. I’d personally lean yes but as always it’s a check with your GM situation.
2nd Level Spells
Hold Person has a lot of potential but your save probably isn’t good enough for you to be casting it, leave it for the rest of the party, but god do I want you to try to point blank auto crit someone with a Cannon.
Darkness is a potential option, you can take Eldritch Adept to get Devilsight and farm advantage inside of your sphere of darkness.
3rd Level Spells
Fly - Worst comes to worse drop a cannon on them. Haste - If your GM rules that the attack action can be used to aim the cannon.
What can our party members help with?
- Artificer: Find an artificer as soon as possible, beg them, plead with them, threaten them. You need to convince them to give your cannon repeating shot. This is your number 1 priority.
- Cleric of the forge: They have a ritual version of magical weapon for a free +1 to hit and damage (but it’s probably better on a weapon that’s going to make more than one attack a turn), their channel divinity can set you up with 10 cannon balls and charges so if they cast it once in down time you’re probably set for most of the campaign, and why don’t you get them to throw on bless too for an extra 1d4 to hit. Hell, their channel divinity works up to 100GP, depending on the setting that might well get you a cannon.
- Thief Rogue: Fast hands, when they’re not busy throwing caltrops and alchemist’s flasks, you can get them to aim your cannon as a bonus action.
- Bards: That bardic inspiration is gonna help keep that Cannon relevant for a few more levels. Creation Bard might be able to keep you on cannonballs and powder too depending on GP costs.
The Build
This is not an optimal build by any stretch of the imagination and relies on some RAW interpretations that a lot of people will disagree with. But it’s a fun thought experiment so I don’t care.
Half Elf Stat Priority: STR/DEX > CON > INT > STR/DEX > WIS > CHA
I have a slight preference for Dex based fighters since Archery Fighting style fundamentally breaks the games bounded accuracy and Dex is free initiative.
Fighter 1 - We get Archery Fighting style (even better if our GM is happy with us adding the +2 to our Cannon).
Fighter 2 - Action surge comes online.
Fighter (Eldritch Knight 3) - Weapon Bond comes online and we get 2 cantrips, we can take one of the Bladetrips to use with war magic later and another of your choice (Mending, Mage Hand and Message are personal recommendations) and three 1st level spells, we’ll take Find Familiar, and the classic duo of Shield and Absorb Elements.
Fighter (Eldritch Knight) 4 - We take Elven Accuracy at level 4, and get our familiar to give us the help action for tri-vantage. We can also pick up Protection from Good and Evil. Then our road forks a little depending on what our GM says.
If we’re happy with Gunner letting us reload for free then we take Eldritch Knight to 6 and get the feat. Hopefully we can even bring them around to letting us use our 2 attacks to aim and fire in the same turn without having to commit to an action surge.
Otherwise we pivot to Fighter (Eldritch Knight) 4 / Artificer 2, and take the Repeating Shot infusion.
After that it’s up to you if you want to all in on fighter, or commit fully to artificer, on either of the builds.
Conclusion
So is the Cannon trick something to worry about at your table? If you let people cast Animate Objects/Conjure animals or take GWM/SS you don’t have to worry about the Cannon Trick. If I saw someone try it at my table, I think I’d probably be glad they wanted to play around with something other than GWM/PAM or SS/CBE.
Let the Eldritch Knight do the silly thing.