The Lockheed S-3 Viking is a 4-crew, twin-engine turbofan-powered jet aircraft that was used by the U.S. Navy (USN) primarily for anti-submarine warfare. In the late 1990s, the S-3B's mission focus shifted to surface warfare and aerial refueling. The Viking also provided electronic warfare and surface surveillance capabilities to a carrier battle group. A carrier-based, subsonic, all-weather, long-range, multi-mission aircraft, it carried automated weapon systems and was capable of extended missions with in-flight refueling. Because of its characteristic sound, it was nicknamed the "War Hoover" after the vacuum cleaner brand.