'Nuff said.
Light Infantry is the branch of the Earth Federation's military that is (mostly) made up of volunteer human-only ground troops. Because of the survivability of Tech Infantry troops in regular battle situations, Light Infantry are often used in support roles during war. When not employed in combat, they are the peacetime police force of the Federation, and specialize in preserving law and order, as well as occupation and peacekeeping operations. When the Five Acts of Arthur Clarke extended universal conscription to non-awakened humans, the Light Infantry was where the majority of the non-awakened draftees ended up, both to support the Tech Infanty in a new wave of conquest, and as military police forces to enforce Clarke's iron grip on power and control over all important aspects of life in the Federation.
Frequently, LI troopers are looked down upon as glorified cops. In fact, standard procedure makes TI rank two levels above any LI rank. This had led to a lot of resentment among the volunteer ranks. This resentment, coupled with the unpopular extension of the draft to non-awakened humans, greatly reduced Light Infantry morale and unit cohesion in the 2250's and 2260's.
Behind the Scenes[]
Light Infantry were first introduced in Season 2 as additional cannon fodder, the two-rank rule allowing for the player characters to run larger-scale operations in the Bug War. Since the Fed is protrayed as a military dictatorship, Marcus thought it would make sense to have them as the national police force. The volunteer aspect makes a pointed difference between that branch and the drafted Tech Infantry. The resentment among humans led to the Ministry of Public Safety faction. Much of the flavor of the depiction of the LI in later seasons of the game is influenced by the Imperial Guard and Planetary Defense Force in Warhammer 40,000.