Executioner from Hell

The Titan Guillotine 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.

Design
Hange's Titan Guillotine was first installed in the southern gate of Trost District. It is comprised of two parallel walls grafted onto the outside of the gate with bars between them to prevent Titans from slipping in. There is a large pulley system with chains fixed atop the Walls that includes a large, heavy log with metal covered sides that rests on top of the Wall. This log is suspended from the pulleys by chains that are pulled by horses from the inner part of the Wall when the log is down.

Eren's hardening powers are needed in order to build the structure. After the proof that the guillotine is a success, Eren decides to help build more of them, even when repeated use of his hardening power makes him feel bad.

System
The system of the Titan Guillotine involves a soldier standing between the two small walls on foot. This draws in near by Titans and once one of the Titans puts their head between the walls to try and get close to the soldier, a command is given and the weighted log is dropped at a high speed on its nape, killing it. The log is then pulled back up into position by the horses and once the Titan's body has evaporated enough, they rerun the system.

The Uprising arc
The first Titan Guillotine 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. One of them, a 12 meter class, tries to enter between the parallel walls. When the Titan is in position, the signal is given and the log is launched, hitting the Titan on its weak spot. After it hits, everybody is waiting for the confirmation of the kill. When it is confirmed that the Titan is dead, everybody celebrates it. Hange says that now they can kill Titans without risk, but when she sees Eren, she is surprised to see him bleeding, due to the fatigue of his shifting training. However, Eren supports the building of these weapons because nobody would have to be eaten again.

Purpose
The Military intends to install Hange's Titan Guillotine all over the Walls and use it to slowly kill off all the Titans within Wall Maria in preparation for the time that they are able to take it back.

Trivia

 * The Titan Guillotine is the first non endangering way to kill Titans that has ever been devised and successfully put into action.
 * The enormous log, way bigger than a regular person, may come from wood of the Forest of Giant Trees.