The Lockheed S-3 Viking is a four-crew, twin-engine turbofan-powered jet aircraft designed and produced by the American aerospace manufacturer Lockheed Corporation. Because of its characteristic sound, it was nicknamed the "War Hoover" after the vacuum cleaner brand. The S-3 was developed in response to the VSX program conducted by the U.S. Navy (USN) to procure a successor anti-submarine warfare (ASW) aircraft to the Grumman S-2 Tracker. It was designed, with assistance from Ling-Temco-Vought (LTV), to be a carrier-based, subsonic, all-weather, long-range, multi-mission aircraft. On 21 January 1972, the prototype YS-3A performed the type's maiden flight. Upon entering regular service during February 1974, it proved to be a reliable workhorse. In the ASW role, the S-3 carried automated weapons and in-flight refueling gear. Further variants, such as the ES-3A Shadow carrier-based electronic intelligence (ELINT) platform, and the US-3A carrier-based utility and cargo transport, arrived during the 1980s and 1990s. In the late 1990s, the S-3B's mission focus shifted to surface warfare and aerial refueling a carrier battle group. It saw combat during the Gulf War of the early 1990s, the Yugoslav Wars of the mid-to-late 1990s, and the War in Afghanistan during the 2000s. The S-3 was removed from front-line fleet service aboard aircraft carriers in January 2009, its missions having been taken over by the P-3C Orion, P-8 Poseidon, SH-60 Seahawk, and F/A-18E/F Super Hornet. For more a decade after that, some S-3s were flown by Air Test and Evaluation Squadron Thirty (VX-30) at Naval Base Ventura County / NAS Point Mugu, California, for range clearance and surveillance operations at the NAVAIR Point Mugu Range. These final examples in U.S. Navy service were retired in early 2016. The last operational S-3 was used by the National Aeronautics and Space Administration (NASA) at its Glenn Research Center until NASA retired it in mid-2021. Most retired S-3s were placed into storage while options for their future were investigated. During the 2010s, Lockheed Martin proposed to refurbish them for carrier onboard delivery. The Republic of Korea Navy also had plans to operate revived S-3s for ASW; these plans were cancelled in 2017. Development In the mid-1960s, the United States Navy (USN) formulated the VSX (Heavier-than-air, Anti-submarine, Experimental) requirement, which sought a dedicated anti-submarine aircraft capable of flying off of its aircraft carriers as a replacement for its existing inventory of piston-engined Grumman S-2 Trackers. The service issued a request for proposals to industry.