The Cyclonic Torpedo is an Imperial weapon of mass destruction that is deployed from a voidcraft into low planetary orbit. There are a wide variant of weapon types covered under the designation of Cyclonic Torpedo, including the Atmospheric Incinerator Torpedo, but all possess the capability to destroy the entire biosphere of the target world, either through the initiation of a thermonuclear reaction that ignites all free oxygen in the atmosphere or the simple expedient of nuclear-fusion-assisted plasma bombardment.
Whatever the exact origin of the mass death to come, the result of these weapons is always the same: the complete destruction of the planetary biosphere, its atmosphere burned away into the void and its oceans boiled to vapor, leaving behind the barren bedrock of a Dead World.
The blast radius is large enough to be seen from space and the detonation usually powerful enough to crack a planet's crust and destabilise its core. The Cyclonic Torpedo is only used by the armed forces of the Imperium of Man to carry out an authorised Exterminatus action on a world that has been deemed to present an extinction-level threat to other inhabited regions of the human-settled galaxy.
The only organisations known within the Imperium to have ordered the use of Cyclonic Torpedoes to carry out an Exterminatus are the Inquisition and the Adeptus Astartes. An Inquisitor has the absolute authority to order an Exterminatus action at any time, and a number of Chapter Masters of the Adeptus Astartes have carried out such regrettable actions under their own authority.
The sacrifice of an entire world and potentially billions of lives is no easy matter for even the often-callous Inquisition; an Inquisitor who orders such an extreme action will have their choices closely scrutinised by their fellow Inquisitors. If they deem the decision to have been unnecessary, the affected Inquisitor may very well find themselves declared a Heretic and hunted down.
Two-Stage Cyclonic Torpedoes
A Two-Stage Cyclonic Torpedo, which is a more exotic form of the standard Cyclonic Torpedo, is the most common of a special class of rare Exterminatus weapons, designed for use against atmosphere-less or biologically-void worlds (certain Necron Tomb Worlds being the main example).
These torpedoes possess two-stage warheads: The first stage is an unusually powerful Melta Charge that bores straight through a planet's crust and mantle to its core. The second stage is a modified Cyclonic Plasma Charge that destabilises it, in most cases physically destroying the planet from the inside out.
- Nightbringer (Novel) by Graham McNeill, Ch. 16, pg. 280
- Tactica Imperialis (Background Book), pg. 66
- Warhammer 40,000: Rulebook (6th Edition), pg. 154