This is largely based upon the official history of the US Counter Intelligence Corps in World War II, which is freely available from the Ike Skelton Combined Arms Research Library online collection (landing page, but you can download the PDF from here). It's been a bit since I read this (about 18 months or so) and I made the grave error of not committing much of my material at the time to writing, but here's a brief summary. I can likely be prevailed upon to expand it if anyone is interested. The World War II US Army's Counter-Intelligence Corps (CIC) was largely a successor to the World War I Counter Intelligence Police (CIP) and as such was, in many ways, more of a field security organization than a counter-intelligence agency (such as the British XX Committee and Security Service aka MI-5). The original CIP was drawn down to 16 personnel following the end of the First World War, resulting in a known capability gap for the US Army as it prepared for World War II. Substantial increases in personnel began in June of 1940 in the expectation of hostilities and continued throughout the war. The Corps of Intelligence Police was renamed to Counter Intelligence Corps effective 1 January, 1942. Planned deployment for the corps was detachment from the corps to Army operational and administrative formations in need of counter-intelligence support down to the division level. A great deal of the history is devoted to organizational, administrative, and training topics I'm not sure are of general interest. I'd be happy to document these in another post if anyone is interested. Initially, the Corps operated in both operational areas and at home, early in the war, the decision was made to focus the Corps on operational activity in the theaters of war, while the FBI focused on Western Hemisphere counter-intelligence generally, and a division of the Provost Marshal in AGF (and its predecessors) focused on security in the Zone of the Interior directly tied to army installations. CIC operations in North Africa focused on acquiring the necessary information to conduct security and counter-intelligence operations, with a great focus on document seizure, which produced good results. In this campaign, the Corps committed to operating at the front with combat formations in order to gain access to necessary documents and personnel immediately. This remained a commitment of the Corps throughout the war and continued to support operational success. Following the occupation, the CIC shifted towards more traditional security and counter-intelligence operations to prevent sabotage targeting US military materiel and espionage against US military operations. This first campaign highlighted the need for linguistic capabilities in the Corps and led to a number of experiments, none of which ultimately proved satisfactory (see below for lessons learned from the history). Much of the operational history focuses on CIC operations in Sicily and Italy, which were quite successful and resulted in the apprehension of large numbers of German and Italian agents dispatched to penetrate allied lines and makes much of the CIC's ability to predict penetration operations. Not to detract from the CIC's achievements, but see my comments at the bottom for discussion of possible advantages CIC possessed that aren't discussed in this official history. CIC's document capture operations establishment of agent nets in captured (and later liberated) areas made its detachments valuable to G-2s up and down the chain of command, acting as an intelligence field force more generally than just as a counter-intelligence organization. CIC also operated more of a field security role in the Middle East early in the war working closely with the British Army's SIME (acronym isn't broken out in the history) though it notes that the British Army equivalent of the CIC was properly their Field Security Service. In the Liberation of France and the Low Countries, some problems experienced in Sicily and Italy with the CIC's expanded role were addressed. Notably, CIC detachments in tactical formations were augmented by CIC personnel from the army level. In addition, since Army doctrine dictated the depth of control exercised by tactical formations behind the front line, this had resulted in turnover of counter-intelligence control of population centers from division CIC detachments (who first established control over the areas) to corps and then to army level detachments. This proved cumbersome and resulted in investigations being interrupted, so it was decided to send specially designated army level CIC elements attached to the division level to maintain control of important population centers until they were ultimately transferred to a zone of occupation. German intelligence and sabotage operations in France the Low Countries appear to have been poorly prepared as the CIC history says that most of their associates either fled or were rounded up by French police or resistance. Therefore, while the Corps appears to have been very successful, it's hard to evaluate how they would have fared against a more committed enemy. In Germany, the Corps' primary objective was to destroy the Werewolf organization and, secondarily, to round up German personnel of interest (NAZI party officials, Abwehr officers, SS personnel) and the CIC's agents found significant aid from local informants. The history provides no clarification as to the motivation of these informants (ideological, monetary, etc...). It's maddeningly vague about combating Werewolf particularly for some reason. CIC's operations in the CBI theater also included being tasked with supervision of document security, after G-2 personnel proved to be insufficiently security minded. There was also quite a bit of field work on assessing lines of communication security. Above, I have sought to hew close to the official history. Below are some remarks from my own perspective. Given that the history was published in the 1940s, little mention of liaison is discussed and no discussion of ULTRA as a source occurs. My suspicion is that the combination of James Jesus Angleton as OSS G-2X (counter-intelligence) in Italy with the ULTRA source contributed. This should not be regarded as detracting from the CIC's successes, but should be seen in the context of intelligence that likely gave them the ability to achieve operational success. It's unfortunate that there's not greater information about combating the Werewolf organization in Germany. This may be due to sensitivities related to the establishment of the Gehlen Organization (and later the BND) related to this. Overall, the Germans don't come across as particularly good at or dedicated to human agent intelligence or sabotage operations. It's unclear to what extent this is due to the Abwehr's lackluster commitment to the war in the West, failure to properly employ German assets (such as the Brandenbergers) or lack of planning by German strategic and operational commanders to establish stay behind intelligence and sabotage networks in occupied territory. The CIC did well, but it's not clear if they would have done as well as they did had they been tested more. From an organizational note, it's important to keep in mind attached units of specialists from GHQ augmented Army tactical formations. If there's interest, this document points to a number of US Army TO&E and TM documents I can also summarize. There's a lessons learned document proper that I will summarize for my own interest which will also include some notes for modellers and artists. I think this on the war game side, these sorts of operations have generally been neglected because they both happened in the shadows and are generally hard to model in game formats. On the model wargaming side, this offers some interesting options for game scenarios (such as assigning a combat formation to escort a CIC outfit to occupy a center of communications, enemy HQ, or establish control of a population center).