Organ Gun

An invention of the Dwarf Engineers Guild, the four-barrelled Organ Gun is so called because its array of barrels resembles the pipes of a musical organ. The Organ Gun's barrels are smaller and lighter than an ordinary cannon's which means it lacks that extreme range and hitting power, but has the advantage of firing a barrage of shots all at the same time. With a well-placed salvo, and all its barrels firing to maximum effect, an Organ Gun has been known to blow away entire enemy units at a time.

Source

 * Armybook: Dwarfs (6th Edition) pg. 18