Canada and the United States would be the best military organization for conducting the raids and strikes; he selected an American, Lieutenant Colonel Robert Tryon Frederick, to assemble, organize, train, and command the U.S.-Canadian 1st Special Service Force.

Made up of three regiments of two battalions each, the unit became a separate branch of the service, with the crossed arrows of the Indian Scouts, by then inactivated, as its insignia. The men were trained in demolitions, rock-climbing, amphibious assault, and ski techniques, and were given basic airborne instruction. They fought under Allied command with great bravery and considerable success in the Aleutians, North Africa, Italy, and southern France. The 1st Special Service Force got its nickname, "The Devil's Brigade," during the Italian campaign from a passage in the captured diary of a dead German officer who had written: "The black devils are all around us every time we come into line and we never hear them." The force was inactivated in southern France near the end of World War II.

On 20 June 1952 the first of the Special Forces groups, the 10th Special Forces Group, was activated at Fort Bragg, North Carolina; it became the nucleus of the Special Warfare Center, now known as the John F. Kennedy Center for Military Assistance, at Fort Bragg. The next unit to be formed was the 77th Special Forces Group, which was also activated at Fort Bragg, on 25 September 1953.

By July 1954 the U.S. Military Assistance Advisory Group, Vietnam, numbered 342. In October of that year President Dwight D. Eisenhower promised direct aid to the government of South Vietnam, headed at that time by Premier Ngo Dinh Diem. From 1954 to 1956 Viet Minh cadres were forming action committees to spread propaganda and to organize the South Vietnamese to oppose their own government. In July 1955 the People's Republic of China announced an agreement to aid the Viet Minh, and the Soviet Union announced aid to Hanoi. In August Diem's government rejected for the third time Hanoi's demands for general elections throughout the two Vietnams, and in October South Vietnam was proclaimed a republic by Premier Diem, who became the first president.

U.S. Special Forces troops actually worked in Vietnam for the first time in 1957. On 24 June 1957 the 1st Special Forces Group was activated on Okinawa, and in the course of the year a team from this unit trained fifty-eight men of the Vietnamese Army at the Commando Training Center in Nha Trang. The trainees would later become the nucleus, as instructors and cadre, for the first Vietnamese Special Forces units.