CLEO uses specialized packages dropped from aircraft containing supplies and marked with a radio beacon to allow them to be located. These beacons produce an audible signal, and thus often attract Zombies, including special infected. It is recommended that the player bring heavy firepower when attempting to retrieve one, particularly later in the game, when these crates are more likely to attract Bloaters or Juggernauts, which cannot be effectively dispatched by running them over in a vehicle.