The 15 Most Secretive Units in U.S. Military History

Unseen by the public, the United States has a long history of clandestine military units operating in the shadows. From World War II to modern conflict zones, these ultra-secretive groups conduct missions shielded from public scrutiny. Many details remain classified, but fragments offer glimpses into their daring operations, elite training, and critical impact. This list explores the most secretive military units in U.S. history, highlighting their unique roles, legendary missions, and enduring mystique.

1. Delta Force (1st SFOD-D)

The 1st Special Forces Operational Detachment-Delta (1st SFOD-D), commonly known as Delta Force, is a premier counterterrorism and hostage rescue unit within the U.S. Army. Established in 1977 by Colonel Charles Beckwith, the unit operates under the Joint Special Operations Command (JSOC) and is headquartered at Fort Bragg, North Carolina. Delta Force’s missions include direct action, special reconnaissance, and operations against high-value targets. Its existence remains unacknowledged by the U.S. government, with details primarily sourced from former members. (britannica.com)

2. SEAL Team Six (DEVGRU)

The United States Naval Special Warfare Development Group (NSWDG), commonly known as SEAL Team Six or DEVGRU, is a premier counterterrorism unit within the U.S. Navy. Established in 1980, it operates under the Joint Special Operations Command (JSOC) and is headquartered at Dam Neck Annex in Virginia Beach, Virginia. DEVGRU’s missions include counterterrorism, hostage rescue, and direct action operations against high-value targets. Its existence remains unacknowledged by the U.S. government, with details primarily sourced from former members. (en.wikipedia.org)

3. CIA Special Activities Center (SAC)

The CIA’s Special Activities Center (SAC) is responsible for covert paramilitary operations, intelligence gathering, sabotage, and reconnaissance. Its operatives, often former military personnel, conduct missions worldwide, frequently blurring the line between intelligence and military action. The New York Times details some of their shadowy history. (nytimes.com)

4. 160th Special Operations Aviation Regiment (Night Stalkers)

The 160th Special Operations Aviation Regiment (Airborne), known as the “Night Stalkers,” provides precision aviation support to elite forces, often operating in darkness using advanced helicopters. Their stealth expertise has been crucial in missions like the 1993 Battle of Mogadishu and the 2011 raid that killed Osama bin Laden. More information is available on the U.S. Army official page.

5. Office of Strategic Services (OSS)

Established during World War II, the Office of Strategic Services (OSS) was America’s first centralized intelligence agency, pioneering espionage, sabotage, and psychological warfare. Its agents operated behind enemy lines in Europe and Asia, gathering intelligence and conducting covert operations. The OSS also developed innovative spy gadgets, influencing future intelligence work. For more, visit the CIA’s history page.

6. 75th Ranger Regiment, Regimental Reconnaissance Company (RRC)

The Regimental Reconnaissance Company (RRC) is the 75th Ranger Regiment’s most elite reconnaissance unit. These handpicked Rangers specialize in infiltration, surveillance, and target designation behind enemy lines, supporting high-risk missions with minimal recognition. Their secrecy rivals other top-tier units. More details at the DVIDS Hub.

7. Air Force 24th Special Tactics Squadron

Reputed as the ‘Delta Force of the Air Force,’ the 24th Special Tactics Squadron comprises Combat Controllers, Pararescuemen, and Tactical Air Control Party specialists. They integrate air and ground operations, frequently attaching to Delta Force or SEAL missions. For more insight, see Task & Purpose.

8. Marine Corps Force Reconnaissance (Force Recon)

Force Recon conducts deep reconnaissance and direct action far ahead of conventional forces. Operating with a high degree of autonomy, its missions often include intelligence gathering, sabotage, and precise strikes. Its ethos and secrecy compare closely to the Army’s Delta or Navy’s SEALs. Check out the USMC Factsheet.

9. Intelligence Support Activity (ISA)

The Intelligence Support Activity (ISA), also known as “The Activity,” specializes in clandestine human intelligence (HUMINT) and signals intelligence (SIGINT) operations. Operating under the Joint Special Operations Command (JSOC), it provides actionable intelligence to elite units like Delta Force and SEAL Team Six. Details about ISA are extremely limited, comparable to British or Israeli special operations intelligence arms. More at The Intercept.

10. 23rd Headquarters Special Troops: Ghost Army

During World War II, the 23rd Headquarters Special Troops, known as the “Ghost Army,” conducted deception operations throughout Europe. Utilizing inflatable tanks, fake radio traffic, and sound effects, they misled Nazi forces about the size and location of Allied units. Their creative and secretive tactics remain legendary. Learn more at the Ghost Army Legacy Project.

11. Mission Support Team (MST), Navy Special Warfare

Part of Navy Special Warfare, Mission Support Teams (MSTs) provide clandestine support such as signals interception, cyber warfare, and rapid intelligence. While less known than SEAL teams, their silent contributions enable mission success against adversaries. For more information, visit the Naval Special Warfare Command website.

12. 1st Special Forces Command (Airborne)—‘The Green Berets’

The 1st Special Forces Command (Airborne), known as the Green Berets, specializes in unconventional warfare, foreign internal defense, and high-value target capture globally. Operating with a high degree of autonomy, their missions often include intelligence gathering, sabotage, and precise strikes. Their ethos and secrecy compare closely to the Army’s Delta or Navy’s SEALs. For more information, visit the U.S. Army Special Forces website.

13. 66th Military Intelligence Brigade

Operating primarily in Europe, the 66th Military Intelligence Brigade supports U.S. and NATO operations through counterintelligence, signals exploitation, and cyber operations—often forming the shadowy backbone of American military presence abroad. For more information, visit the U.S. Army Europe website.

14. Detachment ‘A’ (Berlin Special Forces)

Active during the Cold War, Detachment ‘A’ was a covert U.S. Army Special Forces unit stationed in Berlin, prepared for high-risk sabotage and guerrilla missions in the event of a Soviet invasion. Their secret readiness mirrored other urban special forces units in hostile territory. More at the Army.mil article.

15. 427th Special Operations Squadron

The 427th Special Operations Squadron (427th SOS) is a clandestine unit of the United States Air Force, specializing in short takeoff and landing (STOL) operations. It provides training for U.S. Army Special Operations Forces (SOF) in infiltration and exfiltration techniques, utilizing non-standard aircraft typically found in less developed countries. The squadron is based at Pope Field, North Carolina. For more information, visit the Wikipedia page.

Enduring Mystery and Silent Valor

Despite their concealment, these units have shaped pivotal moments in U.S. and world history—from WWII deception to modern precision raids. Their deeds, often unacknowledged, define the cutting edge of warfighting and intelligence. Revealed only in fragments, their stories illustrate a timeless truth: the most crucial battles are often fought in darkness, shaping global history from the shadows.