Green beret
When visiting the Special Forces at Fort Bragg on 12 October 1961, President John F. Kennedy asked Brigadier General William P. Yarborough to make sure that the men under his command wore green berets for the visit. Later that day, Kennedy sent a memorandum which included the line: "I am sure that the green beret will be a mark of distinction in the trying times ahead". By America's entry into the Vietnam War, the green beret had become a symbol of excellence throughout the US Army. On April 11, 1962 in a White House memorandum to the United States Army, President Kennedy reiterated his view: "The green beret is a symbol of excellence, a badge of courage, a mark of distinction in the fight for freedom". To no avail, both Yarborough and Edson Raff had previously petitioned the Pentagon to allow wearing of the green beret. The President, however, did not fail them.
Delta Force
The origin of the term operator in American special operations comes from the U.S. Army Special Forces (aka the Green Berets). The Army Special Forces was established in 1952, ten years before the Navy SEALs and 25 years before DELTA. Every other modern U.S. special operations unit in the Army, Navy, Air Force and Marines was established after 1977. In "Veritas: Journal of Army Special Operations History", Charles H. Briscoe states that the Army "Special Forces did not misappropriate the appellation. Unbeknownst to most members of the Army Special Operations Force (ARSOF) community, that moniker was adopted by the Special Forces in the mid-1950s." He goes on to state that all qualified enlisted and officers in Special Forces had to "voluntary subscribe to the provisions of the 'Code of the Special Forces Operator' and pledge themselves to its tenets by witnessed signature." This pre-dates every other special operations unit that currently uses the term/title operator.