Three Dimensional Maneuver Gear

The Three Dimensional Maneuver Gear is a set of gear in the Attack on Titan series, developed by humans that allows great mobility when facing the Titans. The gear itself takes the form of a body harness that encompasses much of the body below the neck. Though using it will allow a skilled user great mobility, it carries a large risk of overtaxing the user's muscles, thus special physical conditioning is required to use this gear. Some tools involved in the apparatus include:
 * Handgrips
 * Piston-shot grapple-hooks
 * Gas powered mechanism
 * Iron Wire Propeller with Plug in Blades

Usage
The simplest move possible with the 3DMG is simply aiming and firing the grapple hooks at an object and then activating the gas mechanism to reel oneself toward said object. They can then disconnect the hook and continue moving forward.

Usually however, soldiers must be able to move around in order to navigate in general. Therefore, they tend to use their momentum in order to swing around targets. More advanced techniques include changing directions while still being reeled in as demonstrated by Jean Kirschtein.

Origin
The circumstances regarding the creation of the 3DMG are detailed in the prequel novel Before The Fall. 3DMG was invented by Anheru, a first-class weapons craftsman who worked closely with the Scouting Legion.

Mechanics
The Body of the Device - Steel wire is stored inside the body. There are two axles, which revolve independently. Operating Device - The functioning part of the operating device is a black box, which the technical department manages and improves in secrecy. Body of the Compressed Gas Cylinder - Gas is compressed into the cylinder and injected. Fan Section - Gas is blown directly into the fan to make it rotate. The pressure of the gas is regulated to manipulate the output. Training Three-dimensional maneuver device training is a rigorous process that allows humans, which are limited to two-dimensional movements, to adapt to movement in the third dimension.

Great physical strength, particularly in the legs, coupled with spatial recognition abilities, as well as the mental strength to not waver in the midst of a panic, are crucial qualities.

One of the first things done after enlisting in training is the 3D Maneuver Gear aptitude evaluation. Those unable to remain upright are dismissed.

"Those incapable [of staying upright] aren't suited to even be used as decoys!"

Three years of training is needed before officially becoming a soldier. Many run away or are driven out before graduating. The training is so intense that some people actually die during the process.