A spy reveals all unidentified enemy units in a sector. However, If the enemy also using Radio Silence, a Recon unit is needed to be deployed to identify enemy units within its Line-of-Sight (LOS). This ruse does not reveal the enemy's destination, nor does it reveal units within forests or swamps. It merely spots units that have been detected but not identified - you will still need to use recon to detect hidden units.
Strategies and tactics
The spy ruse can be used to allow fighters and fighter-bombers to target distant units.