As an MDCO, Special Agents of ACI (through ACIC) are recognized federal law enforcement officers tasked with conducting national security criminal investigations in conjunction with other CI activities.

Other CI entities within the DoD not recognized as MDCOs, such as Marine Corps Counterintelligence and the Defense Counterintelligence and Security Agency (DCSA) have no direct criminal investigative mission and therefore are designated only as "intelligence" or "security" organizations; although they may assist in such investigations in a non-law enforcement capacity as authorized by Executive Order 12333 and applicable regulations.

As federal law enforcement officers, they are issued badges and credentials and have apprehension authority under the Uniform Code of Military Justice with regards to U.S. Army Service Members and certain civilians in overseas environments.

These crimes include treason, spying, espionage, sedition, subversion, sabotage or assassination directed by foreign governments/actors, and support to (and acts of) international terrorism.

Most operational ACI Special Agents today work under the auspices of the United States Army Intelligence and Security Command (INSCOM) with ACIC responsible for CI activities and operating Regions, Field Offices, and Resident Agencies world-wide in addition to managing all investigative activity through the Army CI Coordinating Authority (ACICA).

The 650th Military Intelligence Group[7] covers NATO missions in applicable countries under Allied Command Counterintelligence or "ACCI."

[8] ACI was formed as a standing CI service in 1917 during World War I, as the Corps of Intelligence Police (CIP) under the newly created Military Intelligence Division commanded by Colonel Ralph Van Deman following a request to the Chief of Staff of the Army by the American Expeditionary Forces (AEF) G-2, Major Dennis Nolan.

CIP agents provided security for ports in France, England and Scotland; 400 miles of frontier along the borders with Spain and Italy; 31 supply depots; and seven leave centers.

Additionally, some CIP agents worked "Special Projects" in the Counter Espionage Section of the AEF G-2 while also providing security for traveling VIPs and, at times, served as Gen. John Pershing's bodyguards.

Today, ACIC manages investigations worldwide through supported Regions, Field Offices, and Resident Agencies.

Senior ACI Special Agents provide guidance to junior Special Agents and supervise their training; conduct liaison and operational coordination with foreign and U.S. law enforcement, security, and intelligence agencies; plan and conduct counterintelligence operations/activities related to national security; conduct high-profile counterintelligence collection activities and source operations ranging from overt to clandestine collection; supervise/manage surveillance operations; provide support for counterintelligence analytical products, to include preparing counterintelligence reports, estimates, and vulnerability assessments; and with additional training, may conduct technical surveillance countermeasures (TSCM), credibility assessment examinations, or exploit cyber threats.

HET's also conducted CI activities designed to deny, detect and deceive the enemy's ability to target friendly forces.

However, while the HET concept is no longer used, ACI agents will still often work with HUMINT collectors on specific tactical or operational missions.

At this time, ACI Special Agents are authorized, but not required, to attend the Federal Law Enforcement Training Center's (FLETC) Criminal Investigator Training Program (CITP) to function in most duty positions, with the exception of those civilian agents assigned to FBI Joint Terrorism Task Forces (JTTF), FBI Counterintelligence Task Forces (CITF), and some Force Protection Detachments (FPD), that require civilian ACI Special Agents that are also graduates of CITP (also known as one of the federal government's 1811 certification courses).

Army CID is responsible for investigating the more traditional range of criminal activity that most people would associate with the job of a law enforcement officer.

This is likely due in part to the massive size of the U.S. Army when compared to the other military branches, in addition to the long celebrated histories of both organizations.

Given the broad range of CI activities, specific assignments will dictate what clothing is appropriate, which may be civilian attire local to the area of operation.

https://www.congress.gov/bill/118th-congress/house-bill/5009/text H.R.5009 - Servicemember Quality of Life Improvement and National Defense Authorization Act for Fiscal Year 2025: SEC.