During the Vietnam War, the US created a highly classified unit that still influences modern special operations | Business Insider

In 1964, amid the conventional war in South Vietnam, the U.S. created a highly secretive special operations organization, known as the Military Assistance Command Vietnam-Studies and Observations Group (MACV-SOG). This special operations organization was tasked to carry out secret war inside and outside the country, specifically in Cambodia, Laos, and North Vietnam, where the U.S. troops weren’t supposed to be. The group is composed of Navy SEALs, SOG, Green Berets, Recon Marines, and Air Commandos. In the end, the US lost the war, and the group was disbanded, but they have created a lasting impact on the troop and has greatly influenced modern U.S. special operations forces.

Source: https://www.businessinsider.com/macv-sog-created-in-vietnam-still-influences-us-special-operations-2021-2