COMPNOR (short for the Commission for the Preservation of the New Order) was the vicious and fearsome secret police of Palpatine's Galactic Empire. I've always found the Wookipedia page about COMPNOR to be a little confusing with regards to what COMPNOR's various organs do and so I decided to put it into my own words. This is my personal interpretation of what COMPNOR's member groups do.
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COMPNOR
Leadership- Director Ishin Il-Raz
Select Committee
Select Committee- The Select Committee is the shadowy group that controls COMPNOR. The identities of Select Committee members, as well as their overall number, are highly classified and known only to the most senior Imperial officials. The only member of the Select Committee whose existence is known is the Director of COMPNOR. Devoutly loyal to Darth Sidious and devoid of normal Human emotions, the Select Committee is utterly ruthless and willing to commit any atrocity to maintain the power of the Galactic Empire. They are among the worst war criminals and violators of sentient rights in galactic history.
Coalition for Progress- The Coalition for Progress is responsible for data mining and electronic surveillance. This includes reading and listening to all manner of personal communications between citizens and stalking their digital footprints. Any treasonous, seditious, and disloyal communications and materials are flagged and reported to the Imperial Security Bureau and when necessary, the Coalition for Improvements.
Coalition for Improvements- The Coalition for Improvements is responsible for analyzing rebellious worlds then brainstorming and implementing strategies to bring said worlds in line with Imperial rule. These strategies could include altering local government structures, imposing restrictions on local peoples, and even exterminating populations.
Sub-Adult Group- The Sub-Adult Group has two purposes. Its first purpose is to indoctrinate Human children with absolute loyalty to the Empire and unwavering belief in the tenants of the New Order. Its second purpose is to turn children into Imperial spies within their own families. Members of the Sub-Adult Group are taught to report any seditious activity by parents and other family members to COMPNOR.
CompForce- CompForce is an elite military unit trained and controlled by COMPNOR. They are embedded within the larger Imperial military in order to help keep the military loyal to the Imperial government and the doctrines of the New Order.
Imperial Security Bureau- The Imperial Security Bureau is the enforcement arm of COMPNOR. When the other COMPNOR branches identify enemies of state, the ISB eliminates them. The ISB is notorious for arbitrary arrests, forced disappearances, torture, assassination, indefinite detention, summary and mass executions. They operate numerous secret facilities throughout the Galaxy, where COMPNOR's prisoners are held. The ISB also has espionage functions. While the Coalition for Progress is responsible for electronic surveillance, the ISB Surveillance Branch is responsible for planting spies and informants all across Imperial space. Finally, the ISB Internal Affairs Branch serves as the secret police within the secret police, ensuring the members of COMPNOR remain loyal to the Emperor and the Select Committee.