The Executioner from Hell is a large device invented by Hange Zoë for the purpose of killing Titans without the need for soldiers fighting them or the use of cannons and other resources.
Story: The first Executioner from Hell built in Trost is used to prove the effectiveness of the device. Hange invites several reporters and soldiers, so that they can see if the weapon is useful or not by testing it. Several Titans come after detecting a soldier inside the device.
Trivia: The Executioner from Hell is the first risk-free way to kill Titans that has ever been devised and successfully put into action. With the destruction of the Walls due to the triggering of the Rumbling, it is likely that this weapon has been destroyed, as well.
Source: Executioner from Hell, available under CC BY-SA 3.0.