Some creatures have been given a value of '0' (sometimes shown as a dash: '_') for certain characteristics, which means that they have no ability whatsoever in that skill. This usually applies to creatures unable to use missile weapons, so they have BS0, but it might equally well apply to other characteristics too. For example, some creatures or war machines may have no Attacks (A0).
If any creature or object has a Weapon Skill of 0 then it is unable to defend itself in close combat, and any blows struck against it will automatically hit.
If at any time a model's Strength, Toughness or Wounds are reduced to 0 or less by magic or a special rule, it is slain and removed from play.