FBI Director Robert Mueller acknowledged [to the Senate Judiciary Committee on June 19 that] the law enforcement agency uses drone aircraft in the United States for surveillance. He did not say how many unmanned surveillance vehicles (UAVs) the FBI has or how often they have been used. But a law enforcement official told CNN the FBI has used them a little more than a dozen times but did not say when that started. The official said drones are useful in hostage and barricade situations because they operate more quietly and are less visible than traditional aircraft such as helicopters. Bureau spokesman Paul Bresson said their use allows us to learn critical information that otherwise would be difficult to obtain without introducing serious risk to law enforcement personnel." Bresson said the aircraft can only be used to perform surveillance on stationary subjects and the FBI must first get approval from the Federal Aviation Administration to fly in a "very confined geographic area." Senate Intelligence Committee Chairman Dianne Feinstein expressed concern over drone use domestically. "I think the greatest threat to the privacy of Americans is the drone and the use of the drone, and the very few regulations that are on it today and the booming industry of commercial drones," the California Democrat said. The FAA forecasts some 10,000 civilian drones will be in use in the United States within five years, including those for law enforcement and commercial purposes.