The Lockheed S-3 Viking is a four seat jet aircraft that was used by the United States Navy to identify, track, and destroy enemy submarines. 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 the carrier battle group. A carrier-based, subsonic, all-weather, multi-mission aircraft with long range, it carried automated weapon systems, and was capable of extended missions with in-flight refueling. Because of the engines’ low-pitched sound, it was nicknamed the "Hoover" after the vacuum cleaner brand.
The S-3 was retired from front-line fleet service aboard aircraft carriers by the US Navy in January 2009, with its missions being assumed by other platforms such as the P-3C Orion, SH-60 Seahawk, and F/A-18E/F Super Hornet. Several examples continue to be flown by Air Test and Evaluation Squadron THREE ZERO (VX-30) at NAS Point Mugu, California for range clearance and surveillance operations and a single example is operated by the National Aeronautics and Space Administration (NASA) at the NASA Glenn Research Center.
On 20 February 1974, the S-3A officially became operational with the Air Antisubmarine Squadron FORTY-ONE (VS-41), the "Shamrocks," at NAS North Island, California, which served as the initial S-3 Fleet Replacement Squadron (FRS) for both the Atlantic and Pacific Fleets until a separate Atlantic Fleet FRS, VS-27, was established in the 1980s. The first operational cruise of the S-3A took place in 1975 with the VS-21 "Fighting Redtails" aboard USS John F. Kennedy.
Starting in 1991, some S-3As were upgraded to S-3B standard with the addition of a number of new sensors, avionics, and weapons systems, including the capability to launch the AGM-84 Harpoon anti-ship missile. The S-3B could also be fitted with "buddy stores" external fuel tanks that allowed the Viking to refuel other aircraft. 16 S-3As were converted to ES-3A Shadows for carrier-based electronic intelligence (ELINT) duties. Six aircraft, designated US-3A, were converted for a specialized utility and limited cargo COD requirement. Plans were also made to develop the KS-3A carrier-based tanker aircraft to replace the retired KA-6D Intruder, but this program was ultimately cancelled after the conversion of just one early development S-3A.