The Military
Humanity's defence against the Titans is a full-time, professional army trained to deal with Titans. The military is divided into three divisions, each led by their own leaders, but all under the power of Darius Zackly, the Commander-in-Chief of all three.
The Survey Corps(Scouting Legion)"For the Glory of Humanity"
The Survey Corp are tasked with attempting to reclaim territory that has been lost to the Titans.
The Garrison (Stationary Guard) "For Order and Peace"
The Garrison or the The Stationary Guard is responsible for patrolling and protecting the Walls. They are set the task of evacuating citizens in case of an emergency breach in the Walls.
The Military Police "For his Majesty the King"
The Military Police are in charge of keeping order inside the Walls and protecting the King Due to their important function as guardians of the most important humans, only the top 10 trainees from a graduating class are permitted to join them