I seem to recall the plan that involved stopping the escape of any civilians was discussed at an official civil defence type exercise. It also involved a suggestion about ''using local psychopaths to control civilians'' or words to that effect. That latter suggestion didn't seem to gain much traction at the meeting.Nope. Because the Armed Forces would have been busy - either driving to Germany to hold the line against Ivan the Gasman, or guarding all of the KPs that made their logistic support possible. There were no spare troops to be found, anywhere.
That kind of claim tends to come out of the more swivel-eyed tinfoil hat wearer, convinced that "The Establishment" will all have safe spaces in a bunker for themselves and their families, and utterly unwilling to drop a suspicion that the Army (obviously as the joyous fascist bootheel of the Imperialist oppression) would far rather be machine-gunning their own families' refugee convoys than defending the realm or giving the Soviets a good kicking.
I'm sure these documents are online somewhere. Feel free to Google them.