Well... I have seen numerous references to it over the years. It was given widespread exposure in TKDT years ago. It's pretty controversial within hapkido circles for a whole host of reasons
I had dialogue with a couple of CH guys. They both had a king size chip on their shoulder and seemed to think theirs was the ultimate for self defence. One was the guy who claimed he could beat Tyson (and me) up and the other one was the guy who likened me to dog ****
Obviously I was not too impressed. They seem to have an attitude that get's people's back up. For example Brazilian Jiu Jitsu and MMA were two of their pet peeves. Particularly the fact that a Sgt Larssen had introduced MMA training into the army combatives programme. They were both pretty disrespectful about this person.
Things like that seemed to really anger them. No need to guess what they thought the US Army should have been learning.
There's a video on youtube of a CH black belt grading.