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Fortifications & tripwire

1.13 lets you dig in. You can build sandbag barricades and concertina wire in tactical mode, lay minefields, and connect explosives with tripwire networks so that one careless enemy step detonates a whole chain of charges. All three systems were written by Flugente (2012–2016) and are part of every current release — no INI switch needs to be flipped to use them. Together with militia and the interrupt system they turn sector defense into a discipline of its own.

Building fortifications

Fortifications are real map structures: once built, they block movement and lines of fire exactly like the sandbags and walls that map makers place. A prone or crouched merc behind a sandbag barrier gets cover and can rest his weapon on it for better accuracy. Structures can be destroyed by explosives like any other map object.

What you can build

What is buildable is defined in Data-1.13\TableData\Items\StructureConstruct.xml, and what you can tear down (and what materials you get back) in StructureDeconstruct.xml. The stock files currently define:

Structure Built from (item) Removed with Material returned
Sandbags Sandbags, empty Shovel Sandbags, empty (1% status)
Concertina wire Concertina Stack Wire Cutters Concertina Stack (1% status)
Medium debris Wooden Planks (50% status) Shovel Wooden Planks (50% status)
Large debris Wooden Planks (100% status) Shovel Wooden Planks (100% status)
Wooden wall, large Wooden Wall, large Shovel Wooden Wall, large (70% status)

Building consumes the material item's status — a pack of empty sandbags loses 1 point per barrier built, so one 100% pack is good for a long wall. Bobby Ray's sells sandbags and concertina stacks in its miscellaneous section (see Bobby Ray's).

Because the whole system is XML-driven, mods define their own lists: AIMNAS, for example, lets you dig earthworks with a shovel in any map. Tank traps are not in the stock construction list — despite what older wiki pages suggest, in an unmodded install you build sandbags, concertina wire, debris and wooden walls.

Not every map supports every structure

A structure can only be built if its graphics (sandbag.sti, spot_1.sti, ...) are part of the map's tileset. In the current stock data 17 of the 70 tilesets include sandbags — Omerta, the mining towns, Meduna and the underground facilities among them — so in many countryside maps the game will tell you "No fitting fortifications found for tileset...". Map mods like AIMNAS support fortifications almost everywhere, and a community tileset expansion on the Bear's Pit adds sandbags/concertina to stock maps.

Building by hand in tactical

The direct way, useful for a barrier or two in mid-battle:

  1. Put the material item (e.g. empty sandbags) in a merc's main hand.
  2. Click an adjacent free tile. The merc starts building — this is a multi-turn action costing 250 AP by default (AP_FORTIFICATION in APBPConstants.ini), so in combat it carries over across several turns. The structure variant depends on the direction the merc faces.
  3. To tear something down, put the matching tool in hand (shovel for sandbags, wire cutters for concertina) and click the structure — 150 AP (AP_REMOVE_FORTIFICATION).

Merc backgrounds can raise or lower the AP cost (the <ap_fortify> background property, up to ±40%) — see IMP creation for backgrounds in general.

By default the current Ja2_Options.INI allows building during combat (FORTIFICATION_ALLOW_IN_HOSTILE_SECTOR = TRUE). If you set it to FALSE, mercs refuse with "Cannot build while enemies are in this sector!" while enemies are present.

Planning mode and the Fortify assignment

For anything bigger than a single barricade, don't click tile by tile — plan the fortifications and let assigned mercs work through the plan:

Key Effect
Ctrl+Alt+A Open the construction settings dialog: two dropdowns select the structure type (only types this sector's tileset supports are offered) and the exact variant, with a preview image.
Ctrl+A Mark the tile under the cursor for construction of the selected structure.
Ctrl+B Mark the structure under the cursor for removal.
Ctrl+C Open the cover/trap display menu; its Fortification button toggles an overlay of all planned nodes.

Then place mercs in the sector on the Fortify assignment (assignment menu on the strategic screen; the entry is greyed out unless planned work remains in the sector — see Facilities & assignments). Every hour each worker contributes construction points: his effective strength, reduced by fatigue and injuries, and modified by the <fortify_assignment> background property (−50% to +200%). The merc's portrait shows his points per hour and the total still needed in the sector. At the default costs a strong merc (~85 effective strength) manages roughly eleven sandbag tiles' worth of progress per hour — sandbags cost 7.5 points each, concertina 1 point, a large wooden wall 13.

Two things to know about how the work lands:

  • Structures appear when you enter the sector. Progress accumulates while the sector is unloaded, but the map is only changed on your next visit.
  • Materials must be in the sector — lying on the ground or in sector inventory. If they're missing, the game lists the required items when you enter ("Structures could not be built in ... - the following items are required:").

No skill or trait affects construction speed — the current Skills_Settings.INI contains no fortification-related keys; strength (and background) is everything. Mercs on covert ops cannot take the assignment while disguised (see Covert operations).

Fortification plans are files you can share

Plans are saved outside your savegame, as plain text in Profiles\UserProfile_xxx\FortificationPlan\ — one file per sector (e.g. K6.txt, or K6_1.txt for the first underground level). Each line is a node: tile number (shown when you press F on a tile), height level (0 = ground, 1 = roof), build (1) or remove (0), the StructureConstruct.xml/ StructureDeconstruct.xml entry index, and the tile variant. Because the plan is not part of the save, you can design a fortress layout once and reuse it in every campaign — or post it on the forum. With PRINTOUTTILESET = TRUE (the current default), pressing F over a structure also prints its tileset name and index, which is exactly the data you need for these files.

INI settings

From [Tactical Fortification Settings] in the current Ja2_Options.INI (see the options tour):

Key Default Effect
FORTIFICATION_ALLOW_IN_HOSTILE_SECTOR TRUE Allow building/removing fortifications while enemies are in the sector.
ROOF_COLLAPSE TRUE Roofs can collapse when they or their supporting walls are hit.
PRINTOUTTILESET TRUE F over a structure prints its tileset and index (for plan/XML authors).

Related: AP_FORTIFICATION = 250, AP_REMOVE_FORTIFICATION = 150 (and the corresponding BP_ energy costs) in APBPConstants.ini.

A close cousin of this feature: some structures (furniture, barrels, sandbags...) listed in TableData\Items\StructureMove.xml can be dragged to a new position via the Skills menu (A, "drag") instead of being torn down — handy for barricading a door with a cupboard.

Tripwire networks

Tripwire is an item (Bobby Ray's sells single pieces and 100-piece rolls) that is planted like a mine. On its own it does nothing but reveal itself — its power is that it activates other devices:

  • When someone steps on a planted wire, the wire triggers and activates every planted wire on an edge-adjacent tile (north/south/east/west — chains do not spread diagonally).
  • Those wires activate their neighbours in turn: a chain reaction along your whole line.
  • Any planted bomb or mine that is tripwire-activated and sits adjacent to an activated wire detonates. In the stock data this includes tripwire itself, the M18 Claymore, the tripwire grenade mines (below) — the <TripWireActivation> tag in Items.xml decides.

Triggered wire isn't destroyed: it falls to the floor as a normal, unarmed item, so after the battle you can pick your network back up and replant it. Badly damaged wire (status below ~50%) may fail to pass the signal on, so keep your wire in good shape.

Networks and hierarchy levels

Every piece of wire belongs to one of four networks (A–D) and has a hierarchy level (1–4). When you plant wire, a dialog asks you to pick both ("Select tripwire hierarchy (1 - 4) and network (A - D)").

  • A wire only activates wires of the same network. Networks can overlap on the same tiles without interfering — you can run line B straight through line A.
  • Within a network, activation only flows downwards: a triggered wire activates adjacent wires of the same or lower hierarchy level, never higher.

That second rule is what makes layered defenses possible. Say you run a level-1 wire line across your perimeter with a few charges, and behind it a level-3 line wired to your heavy charges, touching the first line. An enemy tripping the outer level-1 line sets off only the outer charges — the level-3 line stays armed. But if anything trips the inner line, the activation cascades down into the level-1 line too and everything goes up at once.

Plant wire fast with Shift

Planting each piece through the network dialog is slow. Hold Shift and click to plant with the previous network settings — and if the merc has more wire in his inventory, the next piece is taken into his hand automatically. Laying a long fence becomes a series of shift-clicks. This also works when planting straight from a tripwire roll: the roll stays in hand and loses 1 status per piece deployed. Wire and rolls convert freely: merge wire pieces into a roll, cut pieces off a roll with a utility knife, or merge a piece onto a partial roll.

Wiring in explosives, grenades and guns

Beyond dedicated mines, three tricks extend what a network can set off:

  • Makeshift grenade mines. Merge a piece of tripwire with a stun, tear gas, mustard gas, mini, MK2 or smoke grenade or an emergency flare to get a plantable "Tripwire ..." mine (e.g. Tripwire Emergency Flare — a self-igniting night alarm). The transformation menu in the item description box ("Remove tripwire") splits it back into grenade and wire.
  • Gun traps. Attach a firearm (no launchers) to a piece of tripwire before planting it. When the wire triggers, the gun fires one shot in the direction the planting merc was facing — with the gun's real range and damage; it heats, degrades, can jam, and needs ammo. Afterwards the gun lies on the floor where the wire was.
  • Explosive attachments. With ALLOW_EXPLOSIVE_ATTACHMENTS = TRUE (default FALSE), a grenade or explosive taped to the wire (rubber band/duct tape) detonates when the wire triggers.

Seeing your networks

You will forget where you put things. The trap display (also reachable via the Ctrl+C menu) is essential; the full key list is in the hotkey reference:

Key Effect
Alt+End (hold) Show your team's planted bombs/mines/tripwire.
Alt+Shift+V Cycle the permanent trap displays: all traps (mines red, wire yellow, both orange) → network colouring (A red, B orange, C yellow, D green) → networks A–D individually (hierarchy 1 green → 4 red) → off.
Alt+Del (hold) / Alt+Shift+C With a metal detector in hand: show all planted devices within 4 tiles — including enemy ones.

There is no [Tripwire] section in Ja2_Options.INI — the system is configured entirely through the item XMLs (<TripWire>, <TripWireActivation>, <TripwireRoll> and <Directional> tags in Items.xml).

Enemy tripwire and defusing

Traps pre-placed by map makers count as an enemy network, and your own display never shows hostile wire — you find it with a metal detector or by inspecting suspicious ground. Defusing tripwire works like disarming any trap (an explosives-based skill check); failing the check activates the wire, so approach someone else's network from the low-hierarchy end or just shoot the charges from a distance.

Mines and minefields

Planting

Any explosive with a pressure detonator can be buried as a mine; dedicated mines (anti-personnel, anti-tank, the bounding mine family) come ready for it. How well a bomb is hidden — its trap level — depends on the planting merc's explosives skill and experience, with a bonus for the Demolitions trait (PLACED_BOMBS_AND_MINES_DETECTION_DIFFICULTY_BONUS = 5 in Skills_Settings.INI; the trait also boosts your bomb damage and planting/removal checks — see Skills & traits). Planting tripwire trains explosives too, just less than planting real bombs, and a botched wire planting at least cannot blow up in your face.

The M18 Claymore deserves its own mention: it is a directional mine (<Directional> in Items.xml). It fires its fragments — 70 of them, 22 damage each, out to about 10 tiles in the current data — in a 60° arc in the direction the planting merc was facing. It can be triggered by pressure, by remote detonator, or by an adjacent tripwire network. Aim it down a lane of concertina wire and you have a proper ambush.

Detecting

A merc may spot mines as he moves; how good he is at it depends on experience level, explosives skill and wisdom, and the Technician trait adds a flat bonus (EFFECTIVE_LEVEL_TO_FIND_TRAPS_BONUS = 2 per trait). A metal detector only works while held in a hand — in current 1.13 having one in a backpack does nothing. In hand it automatically finds nearby buried devices, and with the Alt+Shift+C / Alt+Del display it reveals everything within 4 tiles, friend or foe (items flagged <NoMetalDetection> excepted). Spotted mines get a blue flag planted on the tile; with the current defaults this happens automatically and militia place flags on mines they spot, too:

Ja2_Options.INI key Default Effect
AUTOMATICALLY_FLAG_MINES_WHEN_SPOTTED TRUE Place the blue flag without asking.
MINES_SPOTTED_NO_TALK FALSE Suppress the merc's spotted-a-mine quote.
MILITIA_CAN_PLACE_FLAGS_ON_MINES TRUE Militia flag mines they detect.
CIVILIANS_AVOID_PLAYER_MINES TRUE Neutral civilians know about and walk around your planted devices.

Tiles with your own planted mines and wire are marked for your side, so militia and AI-controlled friendlies path around them instead of stepping on them.

Disarming

Click a discovered device with the hand cursor and you get a four-option menu: Disarm trap, Inspect trap (half cost — a skill estimate from "Safe" to "High danger!"), Remove blue flag, and Blow up! (trigger it deliberately — often the smartest answer to a hostile network). Disarming is a check on explosives skill (plus mechanical under the new trait system) and dexterity; the best "disarm kit" anywhere in the merc's inventory adds its bonus, degraded by its condition — a tool kit gives +15, wire cutters +10, a utility knife +5. Disarmed enemy mines go straight into your stock.

For your own minefields there is a cleaner way: attach a Remote Defuse to bombs before planting and give them all the same defuse frequency (A–D). One use of the remote and the whole field disarms itself, safe to pick up.

Building a killing field

Some verified pieces of advice for putting all of this together:

  • Shape the battlefield before shaping the enemy. Concertina wire is cheap (1 construction point per tile) and blocks infantry paths; use it to close the approaches you don't want defended and funnel attackers into one or two lanes. Fill the lanes with mines and tripwire, and point a claymore down each one.
  • Sandbags are for your shooters, not the enemy. Build them where your mercs and militia will actually stand: a crouched merc behind sandbags gets solid cover and a weapon rest. A machine gunner behind sandbags covering a wire lane is the heart of the suppression game.
  • Let interrupts do the killing. Defenders who stand still with raised weapons win the interrupt race against attackers who spent their turn moving through wire. Fortify, overwatch, and let them come to you.
  • Layer your networks. Outer flare wire (level 1) as an alarm at night, lethal charges on an inner, higher-hierarchy line. You lose only the outer layer to probing attacks — and enemy attacks on your towns arrive in waves, so a defense that survives the first wave matters (see the strategic war for when and where the Queen counterattacks).
  • Mind your own militia. Civilians and militia avoid your devices by default, but a battle is chaos: keep trap lanes and militia positions apart, and clean up fields you no longer need with remote defuses instead of leaving Arulco littered.

Sources