Ship Armament: Spelljammer 5e Conversion


One of my favorite things about the original Spelljammer campaign setting was the inclusion of ship-to-ship combat. This combat is conducted using armament such as ballistae or catapults mounted on weapons decks. Hopefully you’ve already picked out the type of ship that your Spelljamming party is going to sail the stars on (I know my players have). Now you’re going to need to decide which weapons to equip that ship with. This post will convert the armaments from the Spelljammer boxed set for inclusion in a 5e campaign.

Ship armament was originally covered in the Lorebook of the Void included in the Spelljammer campaign set. All of the armament listed in there used 2nd Edition AD&D rules such as THAC0 and Hull Points. Much like I did with the ships from the previous two posts I used updated rules for siege equipment in the 5e DMG as the starting point for this conversion.

The current DMG lists three types of siege equipment that mirror Spelljammer armament; the trebuchet, the cannon and the ballista. The original Spelljammer rules detailed three different types of ballistae so I focused on the cannon and the trebuchet as templates for the conversion. The 5e trebuchet equates directly to the heavy catapult and the 5e cannon equates directly to a bombard.

Ship Armament

NameSizeACHit PointsAttack ModifierRangeDamageIdeal CrewCostNotes
Light CatapultMedium1590+52,500 yds/2,286 m22 (4d10) bludgeoning31,000 gpCan't hit targets within 120 ft. (37 m) of it
Medium CatapultLarge 15120+52,000 yds/1,829 m33 (6d10) bludgeoning42,500 gpCan't hit targets within 90 ft. (27 m) of it
TrebuchetHuge15150+51,500 yds/1,372 m44 (8d10) bludgeoning55,000 gpCounts as two large weapon installations, can't hit targets within 60 ft. (18 m) of it
Light BallistaMedium1530+63,000 yds/2,743 m5 (1d10) piercing2500 gp
Medium BallistaLarge1550+62,000 yds/1,829 m16 (3d10) piercing31,000 gp
Heavy BallistaHuge1570+61,000 yds/914 m27 (5d10) piercing41,500 gpCounts as two large weapon installations
CannonLarge 1975+61,000 yds/914 m44 (8d10) bludgeoing320,000 gp
Light JettisonMedium1590+51,500 yds/ 1,372 m3 (1d6) bludgeoning to all creatures in a 5 ft. (1.5m) radius21,000 gp
Medium JettisonLarge15120+51,000 yds/ 914 m7 (2d6) bludgeoning to all creatures in a 10ft (3 m) radius32, 500 gp
Heavy JettisonHuge15150+5500 yds/ 457 m10 (3d6) blugeoning to all creatures in a 15 ft (4.5 m) radius45, 000 gp Counts as two large weapon installations
Greek Fire ProjectorLarge1980+6500 yds/ 457 m27 (5d10) fire410,000 gpStarts fires

Armament Characteristics

Size- The size categories for this conversion are taken directly from the 5e size categories. I used the trebuchet in the DMG to determine size categories for Spelljammer armament. Heavy weapons fall into the Huge size category, medium weapons are Large and light weapons are Medium.

Armor Class (AC)- The armor class of these weapons will come into play for attacks that directly target them. I determined this AC based off of the materials that each armament is constructed from.

Hit Points- Armament Hit Points determine how much damage the weapons can sustain from direct attacks or area effects before they are destroyed. I converted these Hit Points based off of the trebuchet and cannon.

Attack Modifier- This is the standard attack modifier from 5e. This was determined using the trebuchet and cannon information from the DMG.

Range- The range for these weapons is taken from the original Spelljammer rules. Weapons in space were given expanded ranges since their ammunition spends part of its flight without air resistance.

Damage- This is the damage that the armament deals out. This damage can be against other ships, objects or creatures.

Ideal Crew- This is the number of trained crew members required to operate the weapon at a rate of one attack per round. Each crew member must use their turn during that round to perform their weapon crew task, e.g. loading, aiming, etc. Operating the weapon with less than the ideal crew decreases the rate of fire. For example, a trebuchet with a crew of only four can only fire once every two rounds.

Cost- The cost of outfitting a Spelljammer ship with this weapon type. This cost is taken directly from the original Spelljammer rules.

Spelljammer Armament

Ship armaments are mostly modified from the siege equipment used by ground-based peoples, but the ingenuity of space-faring races has led to new weapons as well. Most ships employ a combination of ranged weapons as well as having a ram installed on the prow of the ship. The armaments on a Spelljammer ship are usually fixed in place restricting their attacks to the three hexes directly in front of them. However, they enjoy a greater range due to the lack of air resistance when firing through the void of space.


Catapults are devices that hurl stones or other heavy ammunition in a high arc. This allows them to hit targets that are behind cover. Unfortunately, the need to arc their shots makes catapults ineffective against targets that are close to them. There are three types of catapults available to equip on a Spelljammer ship.

Light Catapult

The light catapult is the least powerful of the catapults, but is able to hurl stones the farthest. This armament is crewed by a team of three. It takes one action to load the catapult, one to aim it and one to fire it.

Medium Catapult

The medium catapult does more damage than the light catapult, but has a shorter range. A crew of four is required to operate this weapon at peak efficiency. Two actions are required to load the catapult, one to aim it and one to fire it.


The largest of the catapults also does the most damage, but has the shortest range. It takes two actions to load the trebuchet, two to aim it and one to fire it.


Ballistae are large crossbows that fire huge bolts, javelins or spears with exceptional force. These armaments do less damage than catapults, but they have greater range and are able to directly attack any target in front of them. They also require smaller crews than catapults.

Light Ballista

The smallest of the ballistae the light ballista has the farthest range, but does the least amount of damage. It takes one action to load and aim the light ballista and one action to fire it.

Medium Ballista

The medium ballista does more damage than the light ballista, but has a reduced range. It takes one action to load this armament, one to aim it and one to fire it.

Heavy Ballista

The largest of the ballistae has the shortest range, but does the most damage. It requires two actions to load the heavy ballista, one to aim it and one to fire it.


Cannons are one of the most powerful weapons in the known spheres. They do the same amount of damage as a trebuchet, but require a much smaller weapons crew to operate. It takes one action to load a cannon, one to aim it and one to fire it. Cannons require gunpowder to operate. A critical hit against a ship has a 10% chance of igniting gunpowder stores. This makes the storage of large amounts of gunpowder an extremely risky proposition for a Spelljamming crew.


Jettisons are a series of small catapults that hurl large amounts of trash, stones, wood, etc. at enemy ships to clear their decks of personnel. Jettisons do not do any damage against ships.

Light Jettison

The light jettison hurls a barrage of ammunition that impacts in a 5 ft. (1.5 m) radius area. One action is required to load the light jettison, and one action to aim it and fire it.

Medium Jettison

The medium jettison is able to hurl larger size ammunition and a larger amount of ammunition. It does damage to any creature within a 10ft. (3 m) radius area. It takes two actions to load the medium jettison, and one to aim it and fire it.

Heavy Jettison

The heavy jettison is able to clear a 15 ft. (4.5m) radius area of deck with a barrage of ammunition. It takes three actions to load the heavy jettison, and one to aim and fire it.

Greek Fire Projector

Greek fire projectors are useful when two ships come into close contact with each other. The weapons spews forth a stream of liquid that bursts into flame when it hits an object. The liquid lands in a 5 ft. (1.5 m) radius area, but the fire will continue to spread and do damage after the initial attack. Greek fire projectors are extremely dangerous to use in the Phlogiston and only the most desperate of crews would attempt it.


Rams are installed on Spelljammer ships to be utilized in ramming attacks. The cost for the installation of a ram varies depending on the amount of Hit Points a ship has and the type of ram installed. Installation of a piercing ram or a blunt ram costs 5 gold pieces per 25 Hit Points of the ship. Installation of a grappling ram costs 10 gold pieces per 25 Hit Points of the ship. A ram inflicts 1 Hit Point of damage for every 25 Hit Points the ramming ship multiplied by the ship’s SR at the time of ramming. For example, a Galleon traveling at an SR of 5 does 80 points of damage with a ramming attack.

Piercing Ram

The piercing ram is a sharp pointed ram that is designed to break up an enemy ship. In addition to damage from the ramming a successful attack with a piercing ram has a chance to lock the two ships together. This chance is 1% for every 25 Hit Points the target ship has. 

Blunt Ram

The blunt ram is a flattened ram that does standard ram damage. 

Grappling Ram

The grappling ram is a series of movable arms that latch on to an enemy ship after ramming. This causes the ships to be grappled reducing their SR to 0. The grappling ram does not do any ramming damage to the other ship.


Turrets are rotating platforms that armament can be mounted on. Turrets allow all ranged weapons to be fired in a 360 degree range. The cost of a turret varies depending on the size of the weapon mounted to it.
Medium: 250 gp
Large: 500 gp
Huge: 1,000 gp
The turret requires an additional crew member to perform the action to turn it. Installing a weapon on a turret also provides its crew members with half-cover.


That finished up ship armament. Next time I will be covering some pretty dry, but necessary rules such as breathing in space, gravity, and fire in space.


Art credit: Jim Holloway



6 thoughts on “Ship Armament: Spelljammer 5e Conversion”

    1. Each ship has its own plane of gravity. The stone curves as it’s going up out of the launching ship’s gravity, then curves down when it enters the target ship’s gravity. The sights on Spelljammer ship weaponry are calibrated to take that into account.

  1. Not mentioned in this (and you may easily have missed it in the basic books) is that catapults can launch other projectiles than stones. Greek Fire casks, gas globes, and such. Also, Ballistas, in addition to doing damage, can be equipped with cables to “grapple” ships from more than a mile away in order to slow them down and bring the two together for a boarding action. Something to keep in mind when considering weapon choices.

    Lastly, I’m afraid your math doesn’t work out again. If a Galleon, which has 40 tons and 400 Hitpoints does one point of damage for each 25 HP, times its SR, then it should do 16 x 5 SR = 80 damage, not 200.

    Ramming certainly is something needing to be fixed though. It was amongst the most broken mechanics in 2e Spelljammer. Originally, you did your ship’s tonnage in Hull Points (not Hit Points) times your current SR. So a 35 ton Nautiloid moving at a paltry SR of 3 could ram and instantly obliterate an Elven Armada. A 100 ton Illithid Dreadnaught could ram a 300 ton Dwarven Citadel at the same speed (since it’s not “greater than three times your tonnage”) and immediately turn it into floating jetsam.

    The easiest fix would be to make it so you do your ship’s tonnage in *Hit Points*, rather than Hull Points, times speed. Then your ram-equipped galleon of 40 tons moving at SR 5 would indeed do 200 HP damage – a significant chunk out of a Nautiloid, Mindspider, or Hammership, but not enough to “you die now” end combat at a single stroke.

    1. You’re right about the different types of ammunition available. I just didn’t include them for the sake of simplicity. I didn’t want to just rewrite everything that was in the published rules.

      I fixed the numbers for the ramming example, though.

  2. If nothing else, I think the grapple lines out of Ballistas is important because sometimes the other guy is *faster* than you. Besides, boarding gives the party more to do than just “repeatedly fire a weapon while the mage steers the bus”.

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