The Warbeast uses two LEGO Technic motors to keep the gun firing at a constant rate, but the other guns in the book are powered by nothing but rubber bands and physics.
Security expert Roger Cavazos, a former U.S. Army officer, wrote in a report for the Nautilus Institute last year that, among other things, North Korea's big guns have a high rate of firing duds, pose more of a threat to Seoul's less populated outer suburbs, and would be vulnerable to counterattack as soon as they start firing and reveal their location.