Spelljammer

Ship-on-Ship Combat

During ship to ship combat, there are two tiers of combat: ship-to-ship salvos and boarding combat

Initiative Roll

At the start of combat, each pilot makes an initiative roll. Ship initiative in this manner is made as follows

Ship Initiative = 1d20 + pilot level

At the start of initiative, each ship has a speed of 1.

Ship-to-Ship Salvos

Each crewmember on the ship takes action as they wish following general combat rules (1 move, 1 action, 1 bonus action). This allows crew members to  work together to reload/rearm shipboard weapons, repair damage, and fire ranged weapons and spells.

The Pilot Actions

Bonus actions:

• Spellburn (ratchet up initiative): DC n/a - the pilot funnels energy into a spelljamming helm in doing so, causes it to hurtle forward with a sudden, albeit short lived, burst of speed, increasing their imitative order by +5 for every spell level sacrificed. There is no limit to the number of spells that may be sacrificed in this manner, although, only one spell may be sacrificed in this manner  per turn.

The pilot has a special list of normal actions they're allowed to make as they steer their ship.  These DCs are made as follows:

Maneuver Roll = 1d20 + spellcasting ability score + proficiency bonus (if any)

• Maintain Course (normal operation): DC 10 - maintain the ship's present speed and course

• Power to the Helm (accelerate): DC 10 - speed up. If using a spelljamming helm, this requires expending a spell slot. Increase the ship speed by 1. Air ships, blimps, etc. on normal terrestrial worlds max out at a speed of 3. 

• Ease off the Throttle (decelerate): DC 10 - speed slow down. Decrease the ship speed by 1. DC increased by 5 for each additional speed level shed. A failure requires a Dexterity save (DC 20) for ship occupants, or they fall prone and take 4d6 damage  (half on successful save).

• Offensive Maneuvers: DC 20 - all attack rolls from the ship and its crew have advantage against seen/observed ships until the start of the ship's next turn.

• Defensive Maneuvers: DC 20 - all attack rolls made against the ship and its crew by seen/observed ships have disadvantage until the start of the ship's next turn.

• Full Offense: DC 25 - all attacks from the ship are made as if the targets had vulnerability to all damage. All attack rolls made against the ship until the start of the ship’s next turn are made with advantage.

• Full Defense: DC 25 - all attack rolls made against the ship until the start of the ship’s next turn are made as if the targets had resistance to damage. All attacks from the ship until the start of the ship’s next turn are made with disadvantage. 

• Ramming Speed: DC 20 - the attacking ship deals damage equal to it's tonnage multiplied by its ship speed. Any creature within 15 feet of the point of impact must make a dexterity throw (DC 20) or take 4d6 bludgeoning damage and be knocked prone. A successful save reduces the damage by half and they remain on their feed. The attacking ship takes a similar amount of damage, unless the ship specially outfitted for such maneuvers and its crew receives advantage on saves to resist damage and falling prone.

• Evasive Maneuvers (delay action): DC variable - the pilot maintains a state of readiness and seeks to counteract the enemy advantage. If the enemy ship succeeds on their maneuver, the evading pilot makes a counter roll, if they beat the enemy pilot, they negate any advantage the enemy pilot attempted to employ 

The  DCs above are for normal conditions. Environmental factors (exposure to an asteroid field, combat in the phlogiston) may affect the DC listed above, or provide additional options.  On a maneuver failure, the attacks from the ship suffer disadvantage and attacks on the ship gain advantage.

Crew Actions

Crew actions proceed using normal D&D rules (1 move/action/bonus). 

When using large weapons (ballista, catapults, cannons, etc.) it takes time and effort to reload after a successful firing event. Short of marvelous inventions and magic items, there are the following steps involved, requiring one action apiece (and thus, typically three crewmembers):

• Re-arm (draw the ballista, prime a cannon, etc.)

• Re-load (load the ammunition)

• Aim & Fire!

Ship Damage:

In lieu of targeting individuals, crewmembers can target the enemy ship directly. In this case, the damage is made against the ship's AC. Ships are treated as having damage immunity unless the damage from a single attack exceeds the damage threshold, which varies based on the materials used in the ship construction. When damage exceeds the damage threshold, all damage applies normally.

Boarding Combat

Depending the intent of the assailants, they may seek to board the enemy ship. In this scenario, the enemy combatants that end up on another ship complete their action on their ship movement and on the next combat round, act AFTER the ship's crew on the pilot's initiative. Boarding combat works identically to normal D&D rules.

Ending Combat

Combat ends in one of the following ways

• Flee: If at any time, the difference in ship speeds exceeds 4, the faster ship is capable of evading the slower ship and combat ends. Spaces is big and that far away, its is difficult to locate your enemies.

• Ship Destruction: When one ship has been damaged to point of having 0 remaining HP, the ship breaks up. In space , this means the gravity plane is fractures and each creature enters freefall and the atmosphere around the ship drifts away. If combat is conducted inside a gravity well, all occupants and ship debris enters freefall. Falling damage applies normally.

• Purged Crew: When all the crew are slain, the ship maintains its speed and heading and takes no other actions until interrupted by an external force.

• Slain Pilot: When the pilot is slain or loses control of the helm, the ship maintains it speed and heading. Provided no-one takes the helm, the remaining combatants can flee if they so desire or the enemy pilot may make maneuvers with advantage against that ship.