Let's Read “Traveller: Core Rulebook - Space Combat”

For Sci-Fi RPGs, I Envision Spaceship Combat

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A part of my Let’s Read “Traveller: Core Rulebook” series. Go grab your copy of Traveller: Core Rulebook and join in.

In the last chapter, we read about Space Operations. In this chapter, we’ll dive int Space Combat.

Over the years, I’ve written about a few space combats:

I look to the space combat system of a sci-fi game and hope. I hope that the system will create an exhilirating experience and in some way live up to the memories of I have as a child growing up watching Star Wars and Star Trek space battles.

Given my expectations around space combat, I find that the introduction bares repeating:

Clashes between spacecraft in Traveller can involve small, faster craft, zipping between asteroids as they snap laser blasts off at one another, or battles taking place over distances of thousands of kilometres, sometimes over long hours. These battles are slow, calculated affairs, with spears of brilliant light lancing out into the darkness across relativistic distances, aimed at where the enemy is predicted to be.

The former type of battle takes place at short range, often close enough for crews to visually sight their enemy through a viewport. This kind of close ranged ‘knife fight’ uses rules very similar to those used between vehicles, and is summarised at the end of this chapter. It can be likened to swirling aerial dogfights where pilots are flying by the seat of their pants in order to get a shot at the enemy.

Most space combat, however, will take place at ranges far beyond the visual, where distances are so great that even weapons that function at the speed of light have to adjust for relative motion. This kind of battle can be likened to submarine warfare, where decisions have to be weighed and the environment is both methodical and claustrophobic.

This useful separation frames expectations. I often think of spacecraft combat in terms of X-Wings and TIE Fighters, but just as memorable is the Enterprise vs. Reliant in “Star Trek II: The Wrath of Khan.”

Combat Rounds

In space, combat rounds are 6 minutes. We are operating at the scale of 10 to 50,000+ kilometers, so longer combat rounds make sense. A longer combat round is also standard for large scale wargames. Each round has three sequential steps. During each step, each ship performs the given action in initiative order.

The steps are:

  1. Manoeuvre: ships move
  2. Attack: ships attack
  3. Action: crew take actions

Crew Duties

Everyone on a ship has a duty:

Flies ship and performs evasive manoeuvres
Commands ship through Leadership and Tactics
Allocates power, eeks out more power, and fixes stuff
Sensor Operator
Electronic warfare
Operates a single turret or bay of weapons
Ready to board a ship or defend ship from boarders
Unassigned, hanging out in a state room

And the ship’s computer can provide automatic fire, auto-repair, engineering assistance, and piloting.

Starting a Battle

You need to know relative distance between ships. For two ships, this works fine, but I’d imagine this doesn’t work so well for multiple ships. I know in High Guard they introduce a space combat map that addresses this issue. Incidentally, throughout the text, there are a few reference to High Guard. The gist being that the basic rules are adequate for many games, but if you’re focusing on space combat or building out ships, you’ll want High Guard.

Here are the Traveller Range Bands:

1 km or less
1 to 10 km
11 to 1,250 km
1,251 to 10,000 km
10,001 to 25,000 km
Very Long
25,001 to 50,000 km
more than 50,000 km

Due to sensors, most battles start at Very Long or Distant. Actual combat happens when ships enter Medium range or Long Range. A successful ambush may start combat at Close range.


Each ship determines their initiative:

  • Roll 2d6
  • Add the Pilot’s skill
  • Add the ship’s Thrust score

The captain (or commander of the fleet) may make a Tactics (naval) test. Add the Effect to the initiative. If the Captain’s bringing a DM+2 or more to their Tactics (naval) roll, you should always have them roll. The expected value of those rolls is greater than 0. At DM+1, it’s equal odds that they’ll improve or penalize initiative.

In Traveller, surprise in space is difficult. It takes damaged sensors or inattentive operators to miss most ships. It’s possible to use asteroids or other astronomical objects to hide behind.

A surprised ship takes no actions in the first round of combat.

Manoeuvre Step

In initiative order, Pilots allocate Thrust to begin changing range bands, aiding gunners, docking, or allocating for evasive action.

Table 207: Traveller Thrust Required to Change Range Band details the amount of thrust required to change range bands. This works well for one on one encounters. However, with multiple ships, tracking position becomes quite difficult. I know that I loved Diaspora’s one-dimensional map for space combat. I found that to be a useful and meaningful abstraction for tracking multiple ships.

Table 207: Traveller Thrust Required to Change Range Band
Range Band Thrust Required Example
Adjacent 1 Docked ships
Close 1 Dogfighting vessels
Short 2 Ships in same orbital path
Medium 5 Surface to orbit
Long 10 Near to planet
Very Long 25 Within jump limit
Distant 50 Further than the above

As I think on this, I wonder if the manoeuvre step makes sense to declare in reverse initiative order. Those with a lower initiative would declare their maneuvers first. Given that successful Tactics checks can improve your initiative, I would think that the weaker tactician would tip their hand (e.g. declare their maneuvers first).

I ponder this because as I don’t see any advantage to declaring your manoeuvre’s first.

Attack Step

Firing spacecraft weapons use the Gunner skill and associated specialty (eg. bay, ortillery, screen, or capital). For fixed mount weapons, the pilot can fire. In other cases, you need a dedicated gunner for each turret or bay.

The roll is 2d6 + appropriate Gunner skill + Dex DM + range modifiers + weapon bonuses.

There are rules for spacecraft firing at ground targets and vice versa. Spacecraft have DM -2 to hit ground targets, and deal ×10 damage to ground targets. They are also assumed to have Blast 10 trait. Ground targets have DM +2 to hit spacecraft, but deal one-tenth the damage to spacecraft targets.

There are a few different weapon types in the Core Rulebooks, with more in High Guard.

Beam Laser
Continuous fire laser, easier to hit, shorter range
Missile Rack
Very powerful ranged weapons that require time to hit the target
Pulse Laser
Powerful laser blast with longer range and more damage
Defense weapon to protect against lasers

Weapons are mounted in turrets. Ships have a 1 turret per 100 displace tons limit. Each turret can have one, two, or three weapons. A turret that mounts the same weapon-type can fire together, granting bonuses to damage. Alternatively, the turret can mount different weapons, but may only fire one type per round. A small design decision, do you want versatility in weapons or do you want the weapon you choose to pack a heavy punch? I’d imagine in smaller ships you’d go for diversity as you’re limited on the number of turrets. However as the ship size increases, you may have a few turrets that mount the same weapon type.


Weapons deal between 1d6 and 4d6 damage; beam lasers and missiles respectively. With this damage scale, a triple turret that mounts all beam lasers would do 1d6+2, compared to a single 1d6. That’s a no small difference.

On a hit, you add attack roll’s Effect to the damage. If you get an Effect of 6 or more, you inflict a critical hit. Before damage, you subtract the ship’s armour. Hmm…I wonder if ship combats take a lot of time? I suppose I’ll need to playtest a combat.

Critical hits have escalating severity, based on damage done in the attack and damage already sustained at the critical hit location.

You also score a critical hit each time you inflict 10% of the the ships total hull. For ship combat, think of the ships hull displaced tonnage as hit points. In my close reading it appears that one hit could cause two critical hits. First, for a 6+ Effect and second, for inflicting damage that pushes the total damage past a 10% threshold.

The critical hit tables definitely invoke the sense of the Enterprise sustaining heavy damage from a Romulan Bird of Prey.

Critical hit locations are:

  • Sensors
  • Power Plant
  • Fuel
  • Weapon(s)
  • Armour
  • Hull
  • M-Drive
  • Cargo
  • J-Drive
  • Crew
  • Computer


There are three reactions:

Evasive Action
The Pilot, using a point of unspent Thrust, imposes a negative DM equal to the pilot's skill.
Point Defense
The Gunner using a laser not already part of an attack, can attempt to shoot down missiles.
Disperse Sand
The Gunner attempts to "through sand" to reduce the efficacy of incoming lasers. You may also target incoming boarding parties and inflict a whopping 8d6 damage.

Actions Step

Now we get into the actions of available per station.

I’m assuming that the Captain could also make a Leadership check, similar to person to person combat. I don’t see it listed, but I’d definitely allow that. It echoes Stars without Numbers’s “Support Department” action. You read more about command actions in my first and second playtests of Stars without Numbers’s space combat.

I also would’ve thought that there’d be kind of action for the Naval (Tactics).

Improve Initiative
The Captain performs a Leaders check, adding the Effect to initiative of the spacecraft for the next round.
An Engineer makes a quick jump out of the combat.
Offline System
An Engineer makes a check to power down one or more systems.
Overload Drive
An Engineer attempts to increase Thrust for the next round. This gets harder each time you try, and could inflict a critical on your Manoeuvre Drive.
Overload Plant
An Engineer attempts to eek out more power from the power plant. This gets harder each time you try, and could inflict a critical on your Power Plant.
Repair System
An Engineer attempts to jury-rig a fix to mitigate the effea cts of a critical hit.
Reload Turret
A Gunner reloads a depleted missile turret or bay.
Sensor Lock
A Sensor Operator attempts to gain a weapons lock on the target, granting a Boon to attack rolls for the operator's spaceship.
Electronic Warfare
A Sensor Operator attempts to shake a sensor lock, block communications coming from the ship, or nullify missiles.
Boarding Action
A Marine and their fellow marines attempt to storm an Adjacent ship.
Any Traveller can move from one station to another. This takes the whole turn.

Missile Combat

Smart: This weapon has intelligent or semi-intelligent rounds that are able to guide themselves onto a target. They gain a DM to their attack rolls equal to the difference between their TL and that of the target, to a minimum of DM+1 and a maximum of DM+6.

Missiles fired outside of Close have the Smart trait. For Long range, the missile impacts one round after launching. For Very Long, the impact is 4 rounds later. For Distant the impact occurs 10 rounds later. All other ranges, impact is immediate. So watch out for missiles launched at Medium. They keep their Smart trait and impact on the round they’re fired.

A Sensor Operator can attempt a Difficult (10+) Electronics (sensors) check. Any positive Effect destroys or nullifies that many missiles in the salvo.

A ship may also attempt to flee, but there are no specific rules for doing so.

Finally, as the missiles are ready to strike, a Gunner may attempt react with a Point Defense.

Then, the missiles hit. They don’t use any skills. Instead, they need to get an 8+. You apply a DM+1 for each missile that is still in the salvo as well as the Smart trait. Missiles launched at Distant have a DM-6 penalty.

Missile damage is a bit different. Roll damage as though a single missle hit, then deduct armour, and multiply by the Effect of the missile attack. I’m a bit curious about this math, may I’ll grab a sheet of paper and work some of this out. But for now, know that this damage rule appears a bit different than I would’ve assumed.

Close Range Combat

When ships start fire at each other in Close or Adjacent range, the rules shift to a Dogfight. Combat rounds drop from 6 minutes to 6 seconds. If you’re running a massive fleet battle, I don’t think you’ll want to zoom in on this. I do know, having read High Guard, that there are rules for multi-ship combat.

At the start of each round, each spacecraft makes opposed Pilot checks, modified by the ships tonnage; Bigger ships have penalties to the Pilot check.

Table 209: Traveller Dogfighting Modifiers
Dogfighter Modifier
Ship is 50 tons or more -1
Ship is 100 tons or more -2
For every 100 tons more than 100 tons -1
For every additional enemy, after the first, in the dogfight -1
Ship's Thrust +1 per point of Thrust dedicated to dogfighting

In my reading of the above table a 250 ton ship would have a -4 to their Pilot check. There’s also an implication that the Pilot may hold back thrust for Evasive Manoeuvres.

A draw means no one may attack the other with fixed weapons. The winner chooses firing arc orientation for them and any ship they beat on the Pilot check. In addition, the winner gets DM+2 to all firing rolls. The loser gets DM-2 to their rolls. If you win and place your ship in the firing arc of your laser, and outside of a firing arc of another ship, they can’t fire on you. Also, any ship of 100 tons or more has DM-6 to all firing rolls.

We get a brief sub-section detailing a dogfight between spacecraft and vehicles. The rules are there if you need them. They aren’t complicated, but I will not worry about them until I need them.

Reading the Close Range Combat, I definitely get the sense of a dangerous fight.

Boarding Actions

Once two ships are within less than 1 km of each other (Adjacent range), any marines on board can launch a boarding action during the Actions Step. A boarding action takes 2d6 rounds to complete, after which its results are decided.

While it’s not explicit, based on prior rules, at Adjacent range, that 2d6 rounds is combat rounds (e.g. 6 seconds).

Traveller provides a quick resolution to determine the effect of the boarding procedure. The two sides make opposed roles modified by superior equipment, tactics, and numbers. You then check the Boarding Actions table for a quick result. Incidentally, you could easily re-purpose this table for a mass ground combat. It’s abstract and quite useful.


I like that Thrust is a combat round currency for positioning as well as evasive maneouvres. This helps keep the game in the theater of the mind; Though you’ll want something to track relative locations.

When I think about this section and how it might play out, I think about Stars without Number. The space combat rules of Stars without Number favor the player characters. A Warrior’s auto-hit or auto-miss. An Expert’s skill re-roll. Or the default skill ranks of the NPC crews. In Traveller, the Travellers don’t have any innate advantages. There’s a bit of tactics, but fortune will favor the more skillful.

I have some trepidations about weapon damage versus hull points. We get the first inkling of ship sizes (e.g. 100 ton ships, with 100 40 hull points, are a bit large for a dogfight). update: A reader pointed out that this is incorrect. In the core rulebook, there are no instructions on how to calculate hull points. Nor do the example ships list their Hull points. It appears the default formula is hull points are 40% of the ships displaced tonnage. Which changes some of my thoughts.

Assuming 100 40 hull points, those 1d6 and 2d6 points of laser damage seems kind of puny. With some quick napkin math, a Gunner-0 firing a beam laser has an expected damage output of 6, with about a 16% chance of a critical hit due to effect. This assumes that there are no evasive manoeuvres nor sandcasters. A Gunner-2 has an expected damage output of 8, with about a 41% chance of a critical hit.

This appears to mean that a hasty Jump early in a conflict should often be an option. Which is great for Travellers.

In the next chapter we’ll read about the Common Spacecraft.

update: With the correct Hull Points (e.g. 40 instead of 100), it looks like a hasty Jump early in a conflict is still viable, but the likelihood of a critical hit appears higher. The odds of sustaining damage in excess 10% of a ship’s starting Hull Points looks probable; At least for that 100 tonnage example ship.

update: Over on Reddit, someone pointed out in the "High Guard: Space Combat Primer" article in Journal of the Travellers' Aid Society Volume 5. This article provides some tactical advice and synthesis of Space Combat rules from the Traveller: Core Rulebook, High Guard, and Pirates of Drinax.
You don't need all of these to play, but the synthesis in its rephrasing helps clarify the rules. It also includes page references.