The Ghost Army

"Activated on January 20, 1944, the 23rd Headquarters Special Troops, known as the “Ghost Army,” was the first mobile, multimedia, tactical deception unit in US Army history. Consisting of an authorized strength of 82 officers and 1,023 men under the command of Army veteran Colonel Harry L. Reeder, this unique and top-secret unit was capable of simulating two whole divisions—approximately 30,000 men—and used visual, sonic, and radio deception to fool German forces during World War II’s final year."
https://www.nationalww2museum.org/visit/museum-campus-guide/hall-democracy/senator-john-alario-jr-special-exhibition-hall/ghost-army

"The 23rd Headquarters Special Troops, also known as the "Ghost Army," brought together artists, career military officers and audio experts in a unique unit devoted to the art of deception — "the first mobile, multimedia, tactical deception unit in U.S. Army history," according to the National WWII Museum in New Orleans."
https://www.livescience.com/wwii-ghost-army.html

"In 1944, a handpicked group of G.I.s landed in France with truckloads of inflatable tanks, a massive collection of sound effects records and more than a few tricks up their sleeves. They staged a traveling road show of deception on the battlefields of Europe, aimed at Hitler’s legions. From Normandy to the Rhine, the 1100 men of the 23rd Headquarters Special Troops (the Ghost Army) conjured up phony convoys, phantom divisions and make-believe headquarters to fool the enemy about the strength and location of American units. Every move was top secret and their story was hushed up for decades after the war’s end.

Each deception required they impersonate a different (and vastly larger) U.S. unit. These masters of deception mounted an ever-changing multimedia show tailored to each deception. The men immersed themselves in their roles, even hanging out at local cafes and spinning their counterfeit stories for spies lurking in the shadows."
https://www.pbs.org/show/ghost-army/

Operation Fortitude and The Ghost Armies | Secrets of War (WW2 Documentary) | Timeline

The Ghost Army: The mysterious men who tricked the Nazis with inflatable armies in World War II

"The Ghost Army's story was a matter of military secrecy until its declassification in 1996. Now, though, it's the subject of a documentary, the straightforwardly titled Ghost Army."
https://www.theatlantic.com/technology/archive/2013/05/ghost-army-the-inflatable-tanks-that-fooled-hitler/276137/

"The success of the Allied invasion of Normandy during World War II came thanks in large part to a fighting force that didn’t even exist. It was called the Ghost Army, and it convinced the Germans that the forthcoming invasion wasn’t going to take place at Normandy."
https://allthatsinteresting.com/ghost-army-operation-quicksilver

"Skilled in deception tactics, this covert unit of 1,100 service members — 20 hailing from Missouri — were known collectively as the Ghost Army, and they used a variety of unique tactics to keep the enemy off the heels of American Soldiers."

"The unit was comprised of a diverse group of American Soldiers, who came together and bonded to complete covert operations using many tools — the most important of them being creativity."
https://www.army.mil/article/247350/fort_leonard_wood_examines_wwii_ghost_army_deception_tactics