The U.S. Army Special Forces—better known as the “Green Berets” for their signature headgear—have undertaken some of the military’s most sensitive missions. Since their founding in 1952, they’ve operated in war zones from Vietnam to Afghanistan. Distinct from conventional forces, the elite Green Berets work in small teams and specialize in psychological and guerrilla operations.

The original mission of the Green Berets was to conduct unconventional warfare activities designed to disrupt or overthrow enemy governments or occupying powers—often by working with local insurgents. Their responsibilities have expanded to include counterterrorism, surveillance, counterinsurgency training for foreign armies and quick-strike actions such as hostage rescues. In addition, the Green Berets participate in combat search and rescue, counter-narcotic, humanitarian assistance and peacekeeping operations.

Green Berets undergo a rigorous training that begins with a six-week course focused on physical fitness and land navigation. That is typically followed by the Special Forces Assessment and Selection, a grueling three-week test of physical and mental stamina held at North Carolina’s Fort Liberty (formerly Fort Bragg). Selected candidates must then complete the year-long Special Forces Qualification Course that includes instruction in foreign languages, regional cultures, survival techniques and tactical combat skills. The “Q Course” culminates with a four-week training exercise in the forests of North Carolina in which candidates help a guerrilla force overthrow an illegitimate government in the fictional country of Pineland.

The U.S. Army Special Forces originated in 1952 from the special operations units of the Office of Strategic Services (OSS) that supported resistance movements in Europe and Burma during World War II. Their original Cold War purpose was to operate as a stay-behind guerrilla force to work with resistance groups in the event of a Soviet takeover of Western Europe. Initial recruits included OSS special forces veterans and Eastern European immigrants who spoke multiple languages and possessed skills ranging from parachuting to skiing to hand-to-hand combat. “Their skills are an almost-incredible mixture of those needed by the assassin, the frontiersman and the atomic-age soldier,” reported one newspaper.

To distinguish themselves from conventional forces, the U.S. Army Special Forces unofficially adopted green berets, which had been worn by elite U.S. Army Rangers upon their graduation from an intensive commando school in Scotland during World War II. Soldiers donned their berets surreptitiously—until they became part of the official uniform in 1961, when President John F. Kennedy requested they be worn when he visited the U.S. Army Special Warfare Center and School at Fort Bragg.

Believing they could play a valuable role in the Vietnam War, Kennedy was a staunch proponent of the Green Berets. “Kennedy foresaw that wars in the future would not be pitched battles like in World War II and Korea and wanted an elite force of highly trained specialists,” says Marc Leepson, author of Ballad of the Green Beret: The Life and Wars of Staff Sergeant Barry Sadler from the Vietnam War and Pop Stardom to Murder and an Unsolved, Violent Death.

In a 1962 memorandum, Kennedy wrote that “the Green Beret is again becoming a symbol of excellence, a badge of courage, a mark of distinction in the fight for freedom.” Following her husband’s November 1963 assassination, Jacqueline Kennedy requested that the Green Berets join the honor guard at his funeral in recognition of their special bond with the slain president. After Kennedy’s burial, Command Sergeant Major Francis Ruddy placed his own hat on the grave as a sign of respect. “He gave the beret to us,” he said. “We considered it appropriate that it be given back to him.” The Special Warfare Center and School was renamed in Kennedy’s honor, and the Green Berets commemorate his death each year by placing a wreath and green beret on his grave.

During the Vietnam War, the mission of the Green Berets grew from waging guerrilla warfare against conventional forces to assisting a foreign ally in thwarting a guerrilla insurgency. Among the first American troops committed to Vietnam, the Green Berets arrived in 1957 to train 58 members of the South Vietnamese army in counterinsurgency against Communist Viet Cong rebels. By 1967, they were assisting approximately 80,000 paramilitary troops and soldiers.

As part of the Civilian Irregular Defense Group program, the special forces recruited and trained indigenous Vietnamese in the remote highlands to form militias to counter the Viet Cong. In addition to fighting the insurgents and launching cross-border operations into Laos, Cambodia and North Vietnam, the Green Berets built schools, dredged canals and provided medical care to civilians.

One of those Green Beret medics, Staff Sergeant Barry Sadler, propelled the relatively unknown special operations force to fame by producing one of popular music’s most unexpected chart-toppers. Five months into his tour of duty in May 1965, Sadler was impaled by a fecal-covered punji stick planted by the Viet Cong and suffered a severe leg wound and infection that required him to return to Fort Bragg to recover. The lengthy convalescence allowed the aspiring songwriter to complete his patriotic hymn, “The Ballad of the Green Berets,” and land a record deal after recording a demo in a makeshift studio authorized by Special Warfare Center Commander William Yarborough.

Released in January 1966, the soldier’s song became a surprise hit, knocking Nancy Sinatra’s “These Boots Are Made for Walkin’” from the top of the Billboard chart and remaining there for five consecutive weeks. Named Billboard magazine’s #1 single for 1966, it sold an estimated 9 million copies. “The public was still overwhelmingly in support of the war at the time, but that soon changed,” Leepson says. “If the song had come out a year later, it’s very unlikely it would have become a hit. Timing is everything.”

“The Ballad of the Green Berets” proved a publicity bonanza. Although Sadler preferred another tour of duty, the military instead sent him on a recruiting tour of the country. “The Green Berets were a new concept and controversial. Yarborough was very PR-savvy and latched onto this song as a way to gain support among the public, and it worked,” Leepson says. Frustrated with being pulled from active duty, Sadler left the Army in May 1967 with an honorable discharge.

During the 1980s, the focus of the Green Berets shifted to Latin America. There, they trained El Salvador’s army in its civil war with leftist guerrillas, assisted Colombia in combatting narcotics trafficking and joined in the 1989 invasion of Panama that deposed dictator Manuel Noriega.

Just weeks after the attacks of September 11, 2001, the Green Berets were among the first American troops deployed in the U.S.-led War on Terror. Infiltrating mountainous terrain in advance of the invasion of Afghanistan and sometime traveling on horseback, the special forces coordinated the initial bombing campaign. They also assisted the Northern Alliance and tribal forces in overthrowing the Taliban, which had sheltered the al Qaeda terrorist network responsible for the attacks.

The Green Berets joined in the 2003 invasion of Iraq, and, after the fall of dictator Saddam Hussein, they created and trained Iraqi special operations units to fight against the insurgency. In ensuing years, they supported counterterrorism operations in the Philippines, Africa and Latin America.