An Atmospheric Incinerator Torpedo is an Imperial weapon of mass destruction, a variant of the Cyclonic Torpedo, that is deployed from space into low planetary orbit. It will ignite a run-away thermonuclear chain reaction within the atmosphere of the target world that will rapidly consume all the free oxygen, initiating a planetary inferno that will burn the entire biosphere to ash. The Atmospheric Incinerator 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.
This weapon was notably deployed to carry out an Exterminatus action on the world of Medusa IV in the Medusa System in ca. 750.M41. The planet had been overwhelmed by the Forces of Chaos, who were a constant danger due to the Medusa System's proximity to a Warp rift known as Van Grothe's Rapidity, despite the intervention of a number of Imperial forces, including the Ultramarines 2nd Company. The warheads ignited the oxygen-rich atmosphere of the planet, devouring everything in a blistering conflagration that seared all signs of life from the world, turning metal into molten slag and rock to glass as the Inquisition's fiery judgment took its toll. The planet burned brightly for a whole solar month, and from the safety of their own world, the people of Medusa V looked on in awe as their neighbour was consumed in the purifying flames of the Emperor's justice. Those Loyalist citizens of Medusa IV who had escaped offered prayers of gratitude to the Emperor for their deliverance.
During work on the original American atomic bomb at Los Alamos, New Mexico in July 1945, the researchers were aware that there was an chance that the first human detonation of a nuclear device might unleash an uncontrolled fission chain reaction in the Earth's atmosphere. This would produce the planetary inferno very similar to that created by an Atmospheric Incinerator Torpedo. This proved to be an impossibility for various reasons, most critically because atmospheric nitrogen and oxygen cannot produce energy via fission.
- The Fall of Medusa V (2006 Booklet)