Catachan Deathworld armies are experts at booby trapping areas of jungle. Only Deathworld Veteran armies can do this. Deathworld Veterans units in a normal Imperial Guard army cannot lay booby traps.
Placing Booby Traps
Booby traps are bought as Heavy Support options from the army list. Their location is recorded in the same way as for an ambush: divide the table into 1' squares and record the squares which have been trapped. Each booby trap allows you to trap one 1' square. You may set an ambush and lay booby traps in the same square.
Different types of booby trap may be placed in the same square but if a booby trap is set off in a square where there are several booby traps, only one type will be set off. This is determined randomly.
Setting Off Booby Traps
Booby traps are set off when an enemy unit moving through a booby trapped square rolls a double for a Difficult Terrain test, fall back or pursuit move.
Models that roll extra dice for their Difficult Terrain test set off booby traps if they roll any doubles on any two of the dice rolled. Units may choose to roll less dice for Difficult Terrain tests, to lower the chances of setting off a booby trap.
Your opponent chooses which of his models in the booby trapped square sets off the trap. If the unit has models in two or more booby trapped squares only one is set off. The model that sets it off is always the first casualty if damage is caused. The unit, before it moves, then suffers the device's effect as given in the army list.
A booby trap remains effective in the square it has been placed in for the duration of the battle.
Booby Traps and Vehicles
Booby traps affect vehicles that roll a 1 for a Difficult Terrain test in a square where a booby trap has been set. This is in addition to the vehicle becoming immobilised. Vehicles that have dozer blades or rough terrain modifications can re-roll to see if they manage to escape immobilisation but the vehicle will still be affected by the booby trap's effects. Traps and plasma charges hit the vehicle's rear armour.
Locating Booby Traps
Booby traps can be located by troops with an auspex etc, in the same way that an ambush is spotted but this doesn't stop them from working — it just lets you know that the square is booby trapped!
Errata — Chapter Approved: Codex: Catachans Q&A (v1.0): Jump pack troops and bikes die on a roll of 1 on a D6 if they move into difficult terrain. This still triggers a booby trap.