How we change what others think, feel, believe and do
A decoy is a substitute for something real that distracts the enemy.
Build silhouette models that are visible from afar.
Light many campfires at night over a wide area or in a place away from where you are.
Play loud recordings of military movements.
Send false messages and allow them to fall into enemy hands.
Send out trucks dragging long chains that send up long dust clouds.
Drop metal flakes from an aircraft to distract homing missiles.
Decoys can be used to make the enemy think you are somewhere other than where you are, thus drawing their fire or allowing you to get closer without being noticed.
Decoys can also be used to make the enemy think you have more soldiers or armaments than you have.
Decoys thus distract and deceive, causing your enemy to believe things that are not true. This may offer you some protection or distract them from your real intent.
In WW2, model armaments placed near Dover and visible to aircraft were used by Britain to fool the Germans into thinking that the D-Day landings would be near Calais.
Offer the other side some plausible story that sends them on a wild goose chase whilst you move closer to your target.