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Electronic Countermeasures in Traveller

First, there was Original Traveller (c.1977), with its computer programming rules for space combat. These rules were universally disliked by local Traveller gamers as too complex (except for those with computer programming backgrounds, to whom it was too simplistic). Subsequent improvements in real-world (TL8-9) computers also rendered obsolete Traveller's original computers for realism (the "Two tons, 4K of RAM" syndrome).

Mayday (c.1979), a simplified boardgame version of Traveller space combat, introduced an optional "Abstract Computer Rule" where the computer model number simply acted as a DM to hit for both attacker (DM +) and defender (DM -).

By High Guard (c.1980), this Abstract Computer System had become the new standard for Traveller space combat. Relative computer model numbers were used as a DM to hit, replacing the prior system. This system continued through subsequent revisions of Traveller.

Unfortunately, MegaTraveller (c.1987), suffering from GDW's "monstergame carcinoma" of the time, overlaid this system with a complex, hyperdetailed selection of sensors and communicators based on Striker (c.1981), which only metastasized in subsequent revisions until the system became too hyperdetailed to be playable (i.e. Fire, Fusion, and Steel).

Do you remember when CT
Was only Books 1, 2, and 3
And a homespun setting that you wrote?

-- Doug & Kirsten Berry, "The Traveller Saga" (filksong)

These are Homebrew starship Electronic Warfare (EW) rules, based on the Abstract Computer system of High Guard and used in a campaign c.1982-85.


  1. A starship's "computer model" is an abstract rating of all the electronics aboard the ship -- computer, avionics, sensors, and communications.
  2. A ship without a "computer" has basic avionics, sensors, and communications, essentially "Computer Model 0".
  3. Tech levels matter in electronics. A computer of a higher tech level outperforms the same model number of a lower tech level.
  4. Computers Model 1/bis and 2/bis round up to Model 2 and 3 respectively in effectiveness.


  1. Electronic Warfare (EW) Rating: Ships have an EW rating of their Computer Model + Tech Level. This EW rating replaces the Computer Model as the offensive/defensive DM, and represents the ability to jam enemy sensors or burn through enemy jamming.
    1. In a ship with components of different tech levels, the tech level of the Computer determines the EW rating.
  2. New character skill -- EW or ECM: This is a specialized version of the Computer skill available to Navy or Scout veterans, and represents the ability to use EW systems in combat.
    1. Computer skill (for those with other careers) can be used as EW skill at half-value (rounded down); in MegaTraveller or later skill lists, Sensor Operations skill can also be traded in at half-value. Conversely, EW skill can be used as Computer (or Sensor Ops) at half-value.
    2. In Starship combat, the ship's EW Officer (known as the "Old Crow", "Spook", or "Raven") adds his/her EW skill to the ship's EW rating.
  3. Sensors: Sensors are abstracted into two types: Active (emitting detectable energy) or Passive (not emitting). This is an addition to pre-MegaTraveller rules and replaces the elaborate sensor systems in post-MegaTraveller rules.
    1. Detection/tracking ranges are a factor of the sensor type and EW rating. The scale may vary with the actual rev of Traveller; this is the scale for Original Traveller:
    2. A ship can detect another at a base distance of 1/4 light-second per Computer Model number. (The CT detection ranges are based on a "civilian" ship having a Model 1/bis or 2 and a "military/scout" ship having about a Model 6 to 8, plausible for Tech 12+ state-of-the-art.)
      1. If a ship has its sensors Active ("emitting", "lit up", "pinging", or "Yankee-searching"), it can be detected at a range of 2-3x the base range. Once detected, it can be tracked up to 5x the base range. A civilian transponder counts as sensors Active, as it is emitting the ship's registry ID.
      2. If a ship has all its sensors Passive ("radar silence" or "Emcon Alpha"), it cannot be detected until 1/2 the base range. If in close-orbit, 1/4 the base range (lost in the ground clutter). Going passive and launching decoys (missiles with emitter "warheads") or fancy maneuvering into the ground clutter can evade tracking once detected; use the referee's judgement (and sense of drama).
      3. Sensors are assumed to be line-of-sight; getting on the other side of a planet or star (or even an asteroid) completely conceals a ship. (Realistically, a star's radiation output would hide a ship near but not actually behind it; treat the near-vicinity of a star as "fuzzy" for detection purposes.)
      4. Landing on a planet may or may not conceal a ship. If the ship on the ground has been camouflaged, treat as completely concealed; if not, treat as in close-orbit (the ship would still be visible from above).

        Camouflage gets tricky under high-tech passive sensors; for example, TL7 IR sensors defeat the low-tech trick of putting cut foilage over the vehicle/ship and can detect the heat of an operating powerplant; TL8-9 IR sensors can image the heat-traces from vehicle tracks, and TL10+ neutrino sensors can detect a fusion plant in operation. However, diving into a planetary ocean and staying submerged works pretty well; even mass- and magnetic-anomaly sensors would need to close to Distant/Very Distant range (about a km or two) to be sure of detection. Terrain would also be a factor (it's hard to hide sitting on a flat open plain); use the referee's judgement (or dramatic sense) as to whether the ship would be detectible. (Remember the submarine movie schtick of hiding on the bottom while the destroyer above searches with its sonar? The pings getting louder and louder, closer and closer...)

  4. Use of the above in starship combat:
    1. All ships have an EW rating of (Tech Level + Computer Model + EW Officer's EW Skill). If a small craft has no computer, treat as Computer Model 0.
    2. Meson Gun and anti-missile fire must be done with sensors Active, as these weapons require accurate rangefinding.
    3. Non-meson beam weapons and anti-beam sandcaster fire can use Passive sensors. These require only the direction of the target (called "bearing-only data").
    4. Missiles are a special case, and can be fired with either Active or Passive sensors with varying effectiveness:
      1. If fired with sensors Active, the missile uses the EW rating of its firing ship. This represents the ship using its EW assets to defeat ("burn through") enemy jamming and assisting the missiles via a data-link.
      2. If fired with sensors Passive, (to prevent detection of the launching ship), the missile's EW rating is its Tech Level , with no other modifiers. This represents the missile's internal guidance system.
      3. If the firing ship takes a Computer hit, it disrupts the data-link to any missiles in flight; all missiles in flight "go passive" immediately, losing much of their effectiveness.
    5. Fighters (or other small craft) under data-link to their mothership or base (called "GCI" for "Ground-controlled Intercept") behave analogous to missiles. GCI requires the mothership/base to have its sensors Active.
      1. Fighters under GCI use their mothership or base's EW rating.
      2. Fighters not under GCI use their own individual EW ratings.
      3. If the mothership/base takes a computer hit, it disrupts the data-link to its fighters under GCI; any such small craft are no longer under GCI.
      4. GCI can be recovered after such a disruption by either the mothership/base or fighter; the unit with the best character EW skill (usually the mothership/base) must roll 7+ (DM +EW skill level) to re-establish the data-link for each unit. (Under MegaTrav skill system, the referee establishes the basic skill level of re-establishing the link; this should be Routine to Difficult, depending on the intensity of the combat and the damage to the mothership/base's computers).
      5. GCI can be "handed off" to another ship, using the same rules as 4.5.4. This represents another ship (or a suitably-equipped Forward Aerospace Controller) taking onsite command.
    6. Missile and Fighter data-links have a range limit of the base detection range (3.2) and are subject to line-of-sight limitations (3.2.3). More than this, and the lightspeed lag for the data communications causes problems.