I've heard about the 23rd Headquarters Special Troops, commonly known as the "Ghost Army," from various amusing sources on the Internet. [Here is a Wikipedia link about them.]( 23rd Headquarters Special Troops) In short, they were an US regiment of artists who used elaborate props to fool the Germans into thinking they were a real army.
However, for all their elaborate work, how effective was the Ghost Army? Did they fool the Germans? If so, did this cause the Germans to make any major strategic error?
"The Ghost Army of World War II" by Rick Beyer and Elizabeth Sayles (Princeton Architectural Press, 2015) is an excellent source of information about the unit, its makeup, its role in the war, and the fact that it remained virtually unknown for some time after the war because of its secret nature.
According to the authors the unit did help fool and confuse the Germans in several battles, but I don't remember any statements that they made "major strategic errors."
It's well worth reading if you have any interest at all in the role of deception in WWII.
You might also want to investigate some of the works of Ben Macintyre who has written several books on the British use of deception in the war.