Machine invented by Professor Hugo Dante capable of converting heat waves into immense destructive power.
The Inthermo is stolen and its inventor kidnapped by agents of KAOS leader Mr. Big and used to threaten the Statue of Liberty as part of an extortion attempt. Dante is ultimately rescued by Maxwell Smart and Agent 99 but the machine is destroyed when, unable to deactivate it, he reverses it to self-destruct thus destroying the boat that Mr. Big is operating from.
Anticipating the resultant, as he describes it, "blazing inferno" prompts him to declare that he had meant to call the machine "Dante's Inferno", presumably in reference to the epic poem by Dante Alighieri.
[Episode #1: "Mr. Big.]