What was the name of the U.S. military unit known as the 'Ghost Army'?

The 23rd Headquarters Special Troops, also known as the Ghost Army, was the US Army unit responsible for fooling the Germans into believing that the D-Day landings would be at Pas-de-Calais, not Normandy. Their next assignment was to create a fake Mulberry harbor. After that, they were tasked with faking the existence of two 30,000 man Allied armies in France. They accomplished this with inflatable tanks and cars, dummy radio communication, valleys full of tents, and recordings of gunfire, talking, and mechanical sounds. The Germans never discovered the secret of the 23rd.