The Garrison Regiment is the largest branch of the Eldian military, tasked with protecting the Walls and maintaining order within human territory. Positioned between the front lines and the inner sanctums, they are responsible for defensive operations and daily civilian security.

Due to the high mortality rate of the Scout Regiment and the limited positions in the Military Police, most new soldiers choose to join the Garrison. Their duties require frequent interaction with both Titans and civilians, making them highly versatile in the field.

Garrison soldiers are trained in Titan defense tactics, cannon operation, rifle usage, crowd control, and general security detail — ready to respond to breaches or unrest inside the Walls at any time.

The Garrison Regiment is responsible for all defences of the Walls, including patrols, repairs, and improvements. They spend most of their time preparing for attacks against the Wall.

The Garrison also mans the cannons on the Wall, which are often used for long-range Titan defense.

In addition, they handle civilian evacuation and maintain emergency plans for Wall breaches, ensuring that citizens are evacuated safely during attacks.

The Garrison is the largest of the three branches, with a total of 30,000 soldiers. Members of the Cadet Corps are included in this number until their graduation and enlistment in a chosen branch. However, their combat-ready personnel is only 10,000 soldiers, or 1/3 of the total.

Their structure consists of Regiments, Brigades, and Divisions:

• A Regiment = 1,000 soldiers (smallest unit).
  
  

• A Brigade = 2,000–3,000 soldiers (2–3 Regiments).
  
  

• A Division = 2 Brigades (largest unit).
  
  

The Garrison also has an Engineering Corps, in charge of refueling, ammunition, and other support roles. They do not have an insignia and instead wear the regular Garrison uniform. In case of heavy casualties, the Engineering Corps may also be deployed in battle.

For example, during the Battle of Trost, the Engineering Corps worked in Headquarters to refuel ODM gear gas tanks.