Ship Combat

Combat between ships in The Expanse is similar in some regards to combat between characters, but on a much larger (and often slower) scale and more simultaneous in execution than character-scale combat. Space combat uses the following series of steps:
  1. Maneuvers At the start of a round of combat, determine the range between the ships involved. Space combat ranges fall into one of three broad bands: Long Range, Medium Range, and Close Range or CQB (Close Quarters Battle). Range determines effective weapon attacks and defenses. Ships can attempt to maneuver to extend or close the distance between them.

  2. Electronic Warfare Determine the effectiveness of the ship’s sensor information and any efforts to deceive enemy sensors, and therefore targeting, using electronic warfare techniques.

  3. Weapon Attacks All ships involved in the combat select targets and make attacks with their available weapons.

  4. Defensive Actions All targets of weapon attacks take defensive actions, including evasion and the use of point defense weapons.

  5. Attack Damage Resolve the damage of any weapon attack that successfully gets past defenses in Step 5.

  6. Damage Control If a ship is suffers losses due to damage but is not taken out, its crew can attempt to minimize the effects of the losses.

Then repeat the process starting at Step 1 again until all ships on one side of the battle are either taken out or choose to roll over.

A round of space combat tends to be a bit longer than a round of character-scale combat, upward of a minute or so, although the exact time is flexible as with character-scale combat. It’s long enough for all of the ships involved to execute all of the steps listed previously.

For combat to occur between ships, they must be within range of each other’s weapons. Ship combat at the longest range uses torpedoes, then medium range weapons like rail guns, and finally relatively short-distance weapons like point defense cannons, primarily used defensively to shoot down incoming projectiles, but also used offensively in close quarters. If a ship is not within range to use its weapons, it can execute all of the other steps of combat, but cannot effectively attack the opposing ship.

Long Range (100 to 1000 miles or more)
At this distance, self-guided torpedoes are the only really effective weapons, as other attacks are too easy to predict and dodge under normal circumstances.

Medium Range (5 to 100 miles)
At this distance, direct fre weapons like rail guns are effective, whereas they are fairly easy to evade at longer ranges.

Close Range (5 miles or less)
At this distance, a ship’s point defense cannons make effective ship-to-ship weapons for close quarters battle.

Changing Range
In the maneuver phase, ships can shift their relative positions by one range band, moving from Long to Medium Range, for example, or from Short to Medium Range. If a ship wants to maintain the distance between it and a pursuing attacker, roll an opposed Dexterity (Piloting) test between the two ships, with the smaller (and therefore faster and more maneuverable) ship getting a +1 bonus per Size category smaller than the larger ship. So, for example, a Large ship maneuvering against a Gigantic ship has a +2 bonus for being two Size categories smaller. If the maintaining ship wins, the relative range remains unchanged. If the closing ship wins, it decreases by one range band.

High-G Maneuvering
A pilot has the option of going for a high-g maneuver, adding a bonus from +1 to +6 to the maneuver test result and allowing the ship to shift up to two range bands. This puts strain on everyone on board the ship, however, requiring a Constitution (Stamina) test with a TN of 8 + maneuver bonus. On a failure, the character suffers 1d6 penetrating damage per point of maneuver bonus, half that (rounded down) with a successful test. For a +1 bonus, that means a successful Constitution test results in no damage.

In order to effectively fight, a ship must be able to detect its opponents to target and out-maneuver them while working to fool their sensors and present as little of a target as possible. Roll an electronic warfare test for each ship involved in the combat. This is an opposed Technology (Computers) test plus the ship’s Sensors score, against a target number of 11.

Electronic Warfare Test = 3d6 + Technology (Computers) + Sensors vs. TN 11

The winner of the test gains a bonus d6, which can be applied to either defensive actions or the TN to evade the winning ship’s attacks that round. The character performing the electronic warfare test determines how the bonus is divided.

Each round, each of the ship’s weapons within range can attack an available target designated by a crew member with weapons control. Sensor-guided targeting and computer-controlled firing mean a weapon attack within the weapon’s range automatically hits unless the target ship executes a defensive action to evade it  (see Defensive Actions, following).

Ship Weapon Attacks

Grapplers do not inflict damage and can only be used at Close Range (usually a mile or less). A grappler hit that is not evaded locks on to the target ship and, when it moves, the grappling ship moves with it. The grappled ship is treated as having a Size category equal to one greater than the Size of the larger of the two ships, if its drive is moving their total mass. Once a ship is grappled, neither ship can evade the other, which is why grappling is usually only performed on ships unable to fire weapons.

Point Defense Cannons
Primarily defensive weapons, PDCs can be used for attacks at Close Range (5 kilometers or less). A PDC hit does 2d6 damage. If the ship’s PDCs are used to attack that round, the TN for any Point Defense test using them increases by +2 (see Point Defense under Defensive Actions, following).

Laser Cannons
Laser cannons are Medium Range, light-based weapons that can be used to attack enemy ships, but can be used to in conjunction with a ships PDC's to provide Close Range protection against missiles. These weapons do 2d6 damage. If the ship’s Laser Cannons are used to attack that round, the TN for any Point Defense test using them increases by +2 (see Point Defense under Defensive Actions, following).

Rail Guns
Rail guns are useful out to Medium Range, after which their shots are easy to evade. A rail gun attack can only be made against a target in the gun’s firing arc, either in front of or behind the ship (for spinal-mounted rail guns) or along one side of the ship (for turret-mounted rail guns). A rail gun hit does 3d6 damage.

Plasma Cannon
Plasma cannons are powerful Close Range weapons meant to take an enemy out with a single, well placed shot. They deal 3d6+4 damage on a successful hit. On a Snake Eyes roll, the miniature Jump Drive that feeds the plasma cannon fails catastrophically. A character onboard can make a Technology (Repair) test vs. TN 11. One a success the uncontrolled energy release is harmlessly discharged, resulting in the weapon being destroyed but no damage done to the ship. On a failure, the plasma cannon explodes, dealing 2d6 damage to the ship.

Torpedoes are Long Range weapons since they can accelerate faster than any ship, becoming virtually impossible to evade, although they can still be shot down with PDCs. A torpedo hit does 4d6 damage. Plasma torpedoes (see Ship Qualities) do 3d6 damage, but reduce the target ship’s Hull score by one category against their damage.

Torpedo Acceleration
Torpedoes have to accelerate towards their target, using the firing ship’s targeting and their own internal guidance systems. Torpedoes fired at Close Range reach their target on the same round. At longer ranges, it takes the torpedo an additional round per range band, so at Medium Range the torpedo reaches its target on Step 4 of the following round. At Long Range, it reaches its target on Step 4, 2 rounds after launch. On the other hand, torpedoes fired at longer ranges are traveling faster when they reach their targets, making them more difficult—or even impossible—to evade (see Evasion under Defensive Actions, following).

Targeted Weapon Attacks
Weapon attacks are normally assumed to be aimed to inflict the greatest possible damage to their targets. Characters can choose, however, to fire a targeted weapon attack aimed at causing a particular type of loss to the target (see Losses under Attack Damage, following). In this case, a successful attack is reduced by only half of the target’s Hull score (round down after rolling a Hull total) but the attack cannot cause any effect greater than the intended loss, and therefore cannot take out the target ship. Any damage in excess of the intended loss has no effect.

Targeted weapon attacks are sometimes the only effective attacks small ships can make against much larger targets, until they have inflicted enough losses on the target’s systems to give them an advantage. The GM rules if a particular targeted weapon attack is reasonable, given the nature of the target, and may choose to modify the Hull penalty against the target accordingly.

GM NOTE: This is like in some action sci-fi shows where ships will target an enemies' weapons, engine's, or shield generators to disable the ship. And sometimes targeting an enemy ship's life support to get their point across.

Once attacks are declared, targeted ships can take defensive actions. There are two ways to defend against incoming weapon attacks: evasion and point defense.

The targeted ship’s pilot can make a Dexterity (Piloting) test to maneuver the ship out of the path of a weapon attack. The target number is 10 + the attacking ship’s Sensors score, plus any bonus from electronic warfare this round (see the Electronic Warfare step, previously). If the test is successful, the attack misses the ship. If it fails, the attack still hits.

Evasion Test = 3d6 + Dexterity (Piloting) vs. TN 10 + Attacking Ship's Sensors

If outside the weapon’s effective range, an evasion test is automatically successful. Rail gun and PDC rounds don’t just disappear beyond Medium and Close Range—they keep on flying at the same speed through space until they hit something—but evading them becomes child’s play at that distance.

Evading a torpedo actually increases in difficulty with range, as the torpedo accelerates to greater and greater speeds. At Medium Range, the TN to evade a torpedo is 12 + the attacking ship’s Sensors. At Long Range, ships cannot evade torpedoes and can only use point defense to shoot them down, as the torpedoes are moving too fast. If the ship doesn’t have PDCs or Laser Cannons, it cannot defend itself against a Long Range torpedo attack.

High-G Maneuvering
The pilot has the option of going for a high-g evasive maneuver, adding a bonus from +1 to +6 to the maneuver test result, much the same as a high-g maneuver for changing range (see High-g Maneuvering under Maneuvers, previously). This requires the same Constitution (Stamina) test to avoid damage from the maneuver.

A high-g evasive maneuver has another cost—it throws off targeting. If a pilot chooses it, the bonus from the maneuver test also applies as a bonus to the evasion tests of other ships trying to evade the attacks from the pilot’s ship that round.

Point Defense
Ships can also defend against torpedo attacks with point defense and laser cannons, using them to shoot down the incoming attack before it hits. This is a test of the ship’s Sensors, since the reaction time required is faster than the best human gunner. The target number is the same as evasion: 10 + the attacking ship’s Sensors score, plus any bonus from electronic warfare this round.

Point Defense Test = 3d6 + Sensors vs. TN 10 + Attacking Ship's Sensors

If the defending ship’s PDCs were used to attack during the weapon attacks step of the round, the TN for the point defense test is increased by +2 to 12 + the attacking ship’s Sensors. The same applies to the ship's Laser cannons. If a ship is equipped with both PDCs and Laser cannons, one may be held in reserve to provide defense against incoming missiles. Some ship commanders and weapon officers will conserve PDC fire for defensive purposes.

If defensive action fails to prevent an attack, it may inflict damage on the targeted ship. This is similar in many ways to damage against characters. Roll dice equal to the weapon’s damage to determine its effect.

Attack Damage = Weapon Type Dice Roll

The ship can then absorb that damage in a series of steps:

If any damage remains, the ship is taken out.

Hull Total
Generally, the ship’s full Hull score is used against any weapon
damage to the ship, with some exceptions:

If damage remains after subtracting the ship’s Hull total, the ship may suffer one or two losses to further reduce the damage. One loss reduces damage by 1d6 and imposes two of the following loss conditions:

Collateral: Crew members in one compartment of the ship suffer 1d6 damage. If there are crew members in multiple areas, the GM chooses which area(s) are affected.

Hull: Damage to the hull imposes a -1 penalty on Hull score totals (after dice are rolled).

Maneuverability: Damage to the ship’s thrusters or navigation imposes a -1 penalty on Dexterity (Piloting) checks.

Sensors: Damage to the ship’s sensors reduces its Sensors score by 1.

Weapons: Damage to the ship’s weapons imposes a -1 penalty to the target numbers to evade attacks with those weapons and -1 to the weapons' damage.

You can choose the same loss condition twice, in which case its effects stack, such as -2 to Hull score totals or -2 to Sensors, for example. A ship cannot take the same loss condition more than six times total. To determine a loss condition randomly roll 1d6 on the Spaceship Loss Condition table. Re-roll results of 5 if the ship has no weapons.

Two losses reduce damage by 2d6 and impose four of the previous conditions or one of the following serious loss conditions:

Drive Offline: Damage to the ship’s power systems takes the lyrium drive offline; the ship is incapable of high-g maneuvers and suffers a -2 penalty to evasion defensive actions.

Weapon Offline: Damage leaves one of the ship’s weapon systems non-functional. The GM may choose or roll randomly to determine the affected weapon.

Taken Out
If damage remains after applying all losses, then the target ship is taken out. The attacker chooses the target’s condition, ranging from crippled and helpless to destroyed outright.

Rolling Over
The ship’s captain chooses to take the ship out of the encounter, and the player (or GM for a GM-controlled ship) chooses the ship’s condition. As ship can only roll over before the application of damage in a round, although this can be after the defensive action step before damage is calculated and applied.

After a ship takes damage its engineering crew gets to work. On the smallest vessels, an engineer might have only their training, a database of schematics, and a toolkit to work with, but many ships dedicate space near the drive to an engineering bay. A good engineering bay is a machine shop where any part of the ship can be repaired from everything but the most catastrophic damage. A great engineering bay in the hands of a skilled engineer is a place where replacement parts can be fabricated from scratch, if materials are available.

A single loss to Maneuverability, Sensors, or Weapons can be eliminated with a damage control test: Cunning (Engineering) vs. TN 11 and a success threshold of 5. Two losses require a success threshold of 10. Damage control in combat cannot eliminate Collateral or Hull losses.

Damage Control Advanced Test = 3d6 + Cunning (Engineering) vs. TN 11, Success Threshold 5 for One Loss, 10 for Two Losses