Those guys were remarkable Most pilots from the early jets know how to kill dutch roll, but this was an order of magnitude higher.
Many years ago in an L-1011 simulator, at the end of a re-qual session with 15 minutes to spare, I asked the instructor if he would mind if we took a couple of minutes to see what happened if you ignored Lockheeds prohibition of flap use above FL200.
It was almost identical to the TUs antics. Gyratory oscillations that could not be damped by the usual dutch roll kill procedure. We quickly retracted flaps and resolved that this was indeed a very good restriction.