As stated previously, AIU have the duty of assisting its officers and resolve major problems that require Overlook intervention. They tend to serve an advisory role for Divisions, being discouraged from commanding DvLs or below despite being above them in the Combine hierarchy. The loyalty of AIU is to the the Combine faction itself rather than any of its leadership, and are thus entrusted with the ability to remove the Planetary Commander, Sectoral Commander, or both, should they be considered corrupt or otherwise unfit to perform their duties, this being performed by a majority vote within AIU; should both PC and SeC be removed, AIU would be temporarily in charge of finding their replacements. 

While they are not considered humans, these units can be enslaved by the Military Police. 

BACKGROUND LORE

"The AIU are comparable to the Commissars of the old-world. Political officers ensuring absolute loyalty to the cause of their rulers, who punish dissidents harshly, typically with death. The origin and exact design specifications of the AIU is unknown to even Overlook, only that they were provided by the ‘Benefactors’ to act as internal affairs and disciplinary units. Considering the unique designations each AIU has received and evidence of critical thinking ability, there is speculation that AIU are in fact sentient, or even former lifeforms converted into synthetic investigators."

• Official CvR Lore Document

HOW TO COUNTER

• AIU units are incredibly fast and beefy. Keep a close watch of any alternative routes, they may attempt to use them in order to flank you.

• AIU are able to utilize any whitelist within the combine

Current AIU Members

Antonov Directive Unit (ADU): Horkos

AIU Harmacist

AIU Osprey

AIU Supra

AIU Challenger

AIU Joker

AIU Badaim