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Enemy tactical AI

Vanilla JA2 enemies mostly ran at you or hid behind the nearest tree. The 1.13 tactical AI — largely the work of modder sevenfm, whose name still marks dozens of // sevenfm: blocks in the current source — picks positions like a player would, sneaks in the dark, flanks, lays suppression fire, pops smoke over wounded comrades and, if you let it, runs away from a lost fight.

Almost all of it is switchable. The master toggles live in the [Tactical AI Settings] section of Ja2_Options.INI, with a few related keys in other sections. This page explains what you will see on the battlefield, documents every switch with its current default, and tells you which ones to touch for an easier or harder game.

All defaults below were verified against the current GitHub Data-1.13\Ja2_Options.INI and the source code that reads them (Ja2/GameSettings.cpp). See the options tour for INI editing basics.

Where the switches live

File / section What is in it
Ja2_Options.INI → [Tactical AI Settings] The nine behavior toggles documented below
Ja2_Options.INI → [Tactical Interface Settings] NEW_AI_TACTICAL (an older tweak set, documented below)
Ja2_Options.INI → [Tactical Gameplay Settings] AI_SNIPER_* — which soldiers behave as snipers; see Know your enemy
Ja2_Options.INI → [Tactical Suppression Fire Settings] AI_SUPPRESS_* — which weapons the AI will suppress with
TableData\DifficultySettings.xml Per-difficulty AI modifiers (enemy AP bonus, enemy accuracy, radio sightings…)
AI.ini Config for the experimental "Modularized Tactical AI" plug-in system only. Every active team is set to LegacyAIPlanFactory, i.e. the normal AI — there is nothing to tune here.

These settings affect militia too

Several of the toggles are not enemy-only. The movement-mode tweaks apply to enemies and militia, and the pathfinding tweaks apply to every AI-controlled team. Flanking from noise, tactical retreat and the corpse alarm are enemy-team only.

What you will see on the battlefield

Smarter cover and positioning

With AI_BETTER_COVER = TRUE (the default), the position-scoring code that decides where an AI soldier moves gets a stack of extra checks. Soldiers try to avoid:

  • spots their known enemies can see — when defending, they prefer positions where a prone soldier is out of your line of sight, not just behind partial cover;
  • overcrowded locations — nearby friends devalue a spot, so squads spread out instead of bunching up in a doorway;
  • fresh corpses — dead comrades mark a spot as a kill zone;
  • red smoke, which the AI uses to mark artillery strikes;
  • positions with a high chance of friendly fire toward their target.

Zombies and unarmed attackers are rated as extremely dangerous at close range, so armed soldiers keep their distance instead of letting them close in. The "charge forward" bonus that makes aggressive soldiers advance is reduced when the advance would end in the open — and several of these penalties scale with soldier quality, so elites on higher difficulties are noticeably more careful than admins.

Movement that fits the situation

AI_MOVEMENT_MODE = TRUE makes enemies and militia pick their movement animation by context instead of a fixed table. In practice:

  • soldiers walk calmly when no enemy is known, saving energy;
  • they sneak crouched (swat) when seeking you at night, when moving inside buildings or on rooftops near a known threat, and when under fire or shocked;
  • they run across ground that is lit up at night instead of strolling through your flare light, and run for cover while it is still safe to do so;
  • blinded soldiers drop to a crouch and swat away;
  • zombies always run once they know where you are.

AI_PATH_TWEAKS = TRUE adds costs to the AI pathfinder itself (all AI teams): routes through gas clouds, deep water, night-time light and past fresh corpses are avoided when alternatives exist; tanks prefer straight paths, combat jeeps prefer roads, and armed vehicles avoid driving into buildings. See weather, lighting and terrain for how light and gas work.

Flanking

Once enemies are alerted and know roughly where you are (RED alert), flanking is a standard part of their repertoire in current builds — cunning-attitude soldiers pick a left or right arc around your known position instead of advancing head-on. Nothing to configure there.

AI_YELLOW_FLANKING = FALSE controls the extra case: enemies who have only heard a noise (YELLOW alert) trying to flank the noise location. It is off by default — the INI note explains that it can be time consuming when playing covert, and that it makes little sense anyway because in YELLOW state the AI does not know exact enemy locations. Turn it on if you want patrols to circle around suspicious noises, at the cost of longer enemy turns.

Suppression fire

1.13 enemies use real suppression fire, and three switches shape it:

  • AI_EXTRA_SUPPRESSION = TRUE floors the AI's chance-to-hit evaluation at 1%, so an autofire-capable soldier never rejects a suppressive burst as a "0% shot". The INI comment notes this exists mainly for OCTH, where computed hit chances of zero would otherwise stop the AI from firing at all.
  • AI_SAFE_SUPPRESSION = TRUE makes the shooter check his line of fire first: if a visible friend (or neutral) stands in the shooting direction with a meaningful chance of being hit (more than 25% chance for the bullet to get through to him), the suppression attempt is cancelled.
  • AI_SHOOT_UNSEEN = FALSE is the aggressive one: when enabled, AI soldiers fire at the remembered position of an enemy that nobody on their team currently sees — recently seen or heard targets, with the aim point randomized around the last known spot. This is classic "spray the bush he ducked behind" behavior and makes stealth play considerably more dangerous.

Separately, [Tactical Suppression Fire Settings] tells the AI which weapons qualify for suppression at all:

Setting Default Effect
AI_SUPPRESS_MIN_MAG_SIZE 30 Minimum magazine size before the AI considers a weapon for suppression. 0 = any autofire-capable weapon.
AI_SUPPRESS_MIN_AMMO_REMAINING 20 Minimum rounds left in the weapon for it to be used for suppression.

How suppression itself works — shock, AP loss, cowering — is covered on the suppression page.

Smoke, wounded soldiers and retreats

Current builds have built-in self-preservation that needs no INI switch: a soldier who has taken a large hit, or is heavily shocked and caught without cover, will throw a smoke grenade at his own feet and fall back for a few turns; soldiers also throw smoke to screen wounded comrades. Expect fights where the survivor of your opening volley disappears behind smoke instead of standing there to be finished off.

AI_TACTICAL_RETREAT = FALSE goes a step further: when enabled, enemy soldiers whose situation is hopeless treat the map edge as an escape route. A fleeing enemy runs for the closest usable edge and leaves the sector entirely — a tactical traversal, the same way your mercs leave a map — reappearing on the strategic layer instead of dying in place. You lose the kill, the loot and the progress points, which is exactly why it is off by default.

Tactical retreat needs a current build

AI_TACTICAL_RETREAT existed since the end of 2019 but was broken for years — a stray check could deadlock the AI whenever it decided to run away. It was fixed in February 2024 (GitHub PRs #279 and #282). Only enable it on a release from 2024 or later; see version history.

AI morale

Every AI soldier has an internal courage rating — Hopeless, Worried, Normal, Confident or Fearless — that steers how boldly he acts. This is separate from the merc morale system that affects your own team.

AI_NEW_MORALE = TRUE replaces the vanilla calculation with sevenfm's version. On top of the old "who outguns whom" threat comparison, it rates the soldier's own health and energy, whether he is under fire, whether his (or a nearby friend's) last attack actually hit, and caps courage by accumulated suppression shock. Some consequences you can observe:

  • badly wounded, exhausted or blinded soldiers turn cautious and fall back;
  • soldiers whose shots keep connecting press the attack;
  • a disarmed enemy soldier charges with fists or a knife instead of giving up (the old code rated him "hopeless"; the new one deliberately makes him fearless);
  • administrators are made more aggressive than their skill deserves — the code comment literally reads "make idiot administrators more aggressive".

On Insane difficulty, DifficultySettings.xml additionally prevents enemy AI morale from ever dropping below Worried (<EnemyMoraleWorried>), so the army never breaks completely.

The corpse alarm

NEW_AI_TACTICAL = TRUE (in [Tactical Interface Settings]; shipped on, though the code falls back to off if the key is missing) is an older bundle of behaviors that predates the sevenfm block: elites avoid lit places at night, enemies do not run across dead bodies, and — most visibly — an enemy who comes within 5 tiles of a fresh corpse he can see raises a sector-wide RED alert. You get the yellow message "Warning: enemy corpse found!!!" when it happens. Drag your kills out of sight if you want to stay unnoticed; see stealth and night ops. The same switch also lets enemies free comrades you have tied up — relevant if you play with the prisoner system.

Reference: [Tactical AI Settings]

The full section with current defaults, in one place. Comments are condensed from the INI file itself.

Setting Default What it does
AI_TACTICAL_RETREAT FALSE Allow enemy soldiers to retreat from battle via the map edge.
AI_EXTRA_SUPPRESSION TRUE Let the AI shoot more often for suppression (when using OCTH) by faking a minimum CTH of 1 for autofire-capable weapons.
AI_NEW_MORALE TRUE AI morale calculation with additional tweaks (see above).
AI_BETTER_COVER TRUE AI tries to avoid enemy sight, fresh corpses and overcrowded locations when picking positions.
AI_YELLOW_FLANKING FALSE Flanking of heard noises (YELLOW alert). Off by default: time-consuming when playing covert, and in YELLOW state the AI does not know exact enemy locations.
AI_MOVEMENT_MODE TRUE Context-sensitive walk/run/sneak selection for enemies and militia.
AI_PATH_TWEAKS TRUE Experimental pathfinding tweaks: avoid gas, deep water, light at night.
AI_SHOOT_UNSEEN FALSE Allow AI soldiers to shoot at recently seen/heard enemies that nobody on their team currently sees.
AI_SAFE_SUPPRESSION TRUE Extra check to avoid hitting friends when using suppression fire.

Related keys documented elsewhere: AI_SNIPER_RESTRICT_TO_ELITE, AI_SNIPER_MIN_RANGE, AI_SNIPER_CHANCE and AI_SNIPER_CHANCE_WITH_SR (which soldiers hang back and act as snipers) are on the Know your enemy page.

Difficulty and the AI

The INI toggles are the same on every difficulty. What changes per difficulty is in TableData\DifficultySettings.xml — mostly strategic (see the enemy strategic layer), but a handful of tags directly change tactical combat:

Tag Novice Experienced Expert Insane Effect
EnemyAPBonus 0 0 0 5 Extra APs for every enemy soldier (not auto-scaled between the 25/100 AP systems).
CthConstantsAimDifficulty −30 0 +20 +50 Enemy CTH gained per aim click (NCTH only).
CthConstantsBaseDifficulty −30 0 +20 +50 Enemy base CTH from attributes/condition/handling (NCTH only).
CthConstants…Militia +20 +10 0 0 Same two modifiers for your militia.
CthConstants…Player +20 +10 0 0 Same for your mercs, fading out linearly from progress 0 to 30.
RadioSightings 0 1 1 1 Alerted soldiers call in help through the radio.
RadioSightings2 0 1 1 1 All enemy individuals call in help through the radio.
EnemyMoraleWorried 0 0 0 1 Enemy AI morale can never drop below Worried.
MaxMortarsPerTeam 1 1 1 2 Maximum AI soldiers per team (enemy and militia) spawning with a mortar.

So on Insane you are not fighting a smarter AI — you are fighting the same AI with more action points, better aim, a radio net and unbreakable morale.

Making it easier or harder

The defaults are the intended experience. If you want to adjust:

Easier:

  • AI_BETTER_COVER = FALSE — enemies go back to picking naive positions, bunching up and ignoring your sight lines.
  • AI_EXTRA_SUPPRESSION = FALSE — noticeably less incoming suppression under OCTH.
  • AI_MOVEMENT_MODE = FALSE and AI_PATH_TWEAKS = FALSE — enemies walk through light and stumble over corpses again.
  • NEW_AI_TACTICAL = FALSE — no corpse alarm; quiet killing gets much more forgiving.
  • Also look at the per-class enemy bonuses (ELITE_CTH_BONUS_PERCENT, damage resistance and equipment quality) on Know your enemy.

Harder:

  • AI_SHOOT_UNSEEN = TRUE — the single biggest difficulty jump in this section. Ducking behind a wall no longer makes you safe from autofire.
  • AI_YELLOW_FLANKING = TRUE — patrols investigate noises by circling them. Expect longer enemy turns, and avoid it for covert-heavy campaigns.
  • AI_TACTICAL_RETREAT = TRUE — beaten enemies escape with their gear and their lives instead of feeding you kills and loot (2024+ builds only, see above).
  • Raise EnemyAPBonus or the CthConstants… values in DifficultySettings.xml for a stat-based challenge on top.

Where this AI came from

sevenfm started publishing AI experiments on the Bear's Pit in May 2014 in the Experimental Project 7 thread, which grew into Ja2+AI — a complete replacement executable for the old r7609 stable, listed as 7609+AI on the mods page. From late 2015 onward his improvements were merged into the 1.13 trunk in stages, and the named toggles arrived in two waves:

  • 2015–2016: a big flanking rework was merged without a switch (November 2015); AI_EXTRA_SUPPRESSION, AI_NEW_MORALE and AI_BETTER_COVER followed as opt-in experiments in December 2015 (SVN r8006), and AI_YELLOW_FLANKING in May 2016.
  • 2019–2021: AI_TACTICAL_RETREAT (December 2019), AI_MOVEMENT_MODE and AI_PATH_TWEAKS (January 2020 — the AI_PATH_TWEAKS commit also flipped the 2015-era toggles and AI_MOVEMENT_MODE to on-by-default), AI_SHOOT_UNSEEN (August 2020) and AI_SAFE_SUPPRESSION (October 2020). The AI_NEW_MORALE calculation got its current shock-aware form in October 2021.

sevenfm has since left the community, but the code is maintained by the current GitHub team — the 2024 tactical-retreat fix is a good example. Note that the standalone Ja2+AI executable contains behavior that differs from stock 1.13 (its FAQ describes automatic canteen refills and stricter disguise-color rules, for example), so old forum descriptions of "+AI" do not necessarily describe what your current build does.

Sources