Terror Drone Surprise is a Soviet Top Secret Protocol. This protocol allows Soviet commanders to place Terror Drones in their vehicles which are released when the vehicles are destroyed. In the game, whenever a vehicle is destroyed, there is a 75% chance that a Terror Drone will spawn in the wreckage of the vehicle. This upgrade is especially dangerous toward Tanya (though in newer patches, Tanya can destroy Terror Drones) and melee units such as the Steel Ronin and Grinder. This upgrade is also needed to unlock the Toxic Corrosion and Orbital Drop/Dump/Downpour Support Powers in skirmish mode and in the Commander's Challenge in Uprising.
This makes all Soviet ground units very dangerous to crush or destroy with a melee unit as the drone will immediately infect the attacker. Does not count towards infantry, aircraft, submerged units, as well as Sputniks. Higher tier units have an increased chance of spawning a Terror Drone than lower tier units. Units that are shattered under the effects of Cryo Technology will not grant a Terror Drone.