I'll just give you the wiki synopsis. It's well worth watching if you like WWII history and have Prime. The stuff they did was a low tech tactic but still sort of high tech.
The documentary tells the history of the secret U.S. Army unit of 1100 troops that was set up in 1944 and operated until 1945 in the final stages of World War II in the fight against German troops in various parts of Europe. They used a combination of different ways of visual, sonic and radio deception to convince the enemy of the presence of specific Army units that were in fact operating elsewhere. The unit included a large number of visual artists and designers who documented their experiences in paintings and sketches. The materiel employed in the 23rd Army Headquarters Special Troops' operations included decoys such as inflatable rubber tanks and jeeps as well as powerful loudspeaker trucks playing sound recordings of troop activity.
Ghost Army - Amazon Prime Documentory
They aren't sure how great an impact it had, but the unit probably saved quite a few American lives. Probably didn't turn the tides of any battles, but made them much easier for the allies by thinning the Nazi lines. A number of captured maps showed the ghost army on their maps and as large groups. Also fake patched some holes in the allied lines until real tanks and troops could get there.
Pretty neat stuff.
Pretty neat stuff.
"... and then I was forced to walk the Trail of Tears." - Elizabeth Warren