The ability for foreigners to blend in was a skill that an American just could not possess. Bob Charet joined the Det A as a Green Beret and served the United States. He described his missions that he did in Det A as being a “Poor man’s James Bond”. His first deployment happened to be in Vietnam where he watched his teammate get killed. He spent time back in Berlin training in counterterrorism and eventually used his skills in the CIA.
Source: https://connectingvets.radio.com/articles/bob-charest-on-special-forces-detachment-a-in-berlin