From D-Day to the crossing of the Rhine, the Army's top-secret 23rd Headquarters Special Troops unit used inflatable tanks, trucks and artillery pieces; bogus radio traffic; 500-pound loudspeakers blasting recordings of divisions on the move; and other means of fakery to confuse the Nazis. In the process, it may have saved the lives of 15,000 to 30,000 American troops, according to Army historians.