Melta Cannon

The Melta Cannon is an Imperial plasma weapon that make use of a miniature fusion reaction to produce a blast of intense, searing heat. This weapon system is commonly mounted on Reaver-class and Warlord-class Titans, but can be mounted on the carapace hardpoints of an Imperator-class Titan. A smaller version of this weapon system is also mounted upon the Devil Dog-pattern Chimera.

Operation
The Melta Cannon works by sub-molecular thermal agitation in a manner comparable to microwave irradiation. This formidable heat-based plasma weapon works by inducing a minute, sub-molecular nuclear fusion reaction within a highly pressurized pyrum-petrol fuel mix, and then projects the resulting plasma from the barrel as a blast of super-intense heat, melting plasteel or plascrete, and its devastating effects instantaneously evaporate living tissue, as all the moisture vapourises explosively. The Melta Cannon makes no noise when fired, but the super-heating of the air produces a distinctive hiss which becomes a roaring blast. The one drawback to this weapon is that it can only be used effectively at close range, so it is mostly used for close assault and support.

Source

 * Adeptus Titanicus (1st Edition)
 * Apocalypse
 * Titanicus (Novel) by Dan Abentt
 * Warhammer 40,000 Wargear (2nd Edition) p. 26