Stone throwers, bolt throwers and cannons are common to several armies, but in addition there are many strange war machines that are available only to specific armies. These are described in the Warhammer Armies books together with the special rules that apply to them. Examples include Dwarf Flame Cannons that spout a sheet of flames, undead catapults firing screaming skulls, and the deadly Helblaster Volley Guns of the Empire.
Some of these unique war machines are so different that they have entirely new rules, but others are similar to the machines described above in that they consist of a weapon and its crew. In general, the same rules apply to these crews as to the crews of stone throwers, cannons and bolt throwers. Exceptions to these procedures, together with the special rules for the weapons, are described in the appropriate Warhammer Armies books