A bolt thrower is a powerful weapon which can hurl its bolt through several ranks of troops, piercing each warrior in turn. If you hit then resolve damage against the target using the bolt thrower's full Strength of 5. If the model is slain then the bolt hits the trooper in the second rank directly behind: resolve damage on the second model with a Strength of 4. If the second rank trooper is slain then a model in the third rank is hit: resolve damage with a Strength of 3. Continue to work out damage as the bolt pierces and slays a model in each rank, deducting -1 from the Strength for each rank pierced.
A model damaged by a bolt thrower sustains not 1 but D4 wounds, which means that even large monsters can be hurt or slain by a hit from a bolt thrower. Armour saves are not allowed for hits from a bolt thrower, because the missiles are so fast and deadly that any armour is pierced along with its wearer. Because saves are not taken a target with only 1 wound will be slain if it takes damage, there is therefore no need to roll the D4 to decide the number of wounds.