Lockheed S-3 Viking

The Lockheed S-3 Viking is a four-crew, twin-engine turbofan-powered subsonic anti-submarine 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 than 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.

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. During August 1968, a team led by Lockheed, as well as a rival team comprising Convair and Grumman, were requested to further develop their proposals to meet this requirement.

At this stage, Lockheed recognised that it had little experience in designing carrier based aircraft, thus the company reached out to the industrial conglomerate Ling-Temco-Vought (LTV), which joined the team. LTV assumed responsibility for the design of various elements of the airframe, such as the folding wings and tail, the engine nacelles, and the landing gear, some of which had been derived from the earlier LTV A-7 Corsair II and Vought F-8 Crusader. Sperry Univac Federal Systems was assigned the task of developing the aircraft's onboard computers which integrated input from sensors and sonobuoys.

On 4 August 1969, Lockheed's design was selected as the winner of the VSX contest; an order for eight prototypes, designated YS-3A, was promptly received by the company. On 21 January 1972, the first prototype performed its maiden flight in the hands of military test pilot John Christiansen. Flight testing proceeded quickly with no major issues; two years later, the S-3 entered operational service with the U.S. Navy. During the type's production run, which ran from 1974 to 1978, a total of 186 S-3As were constructed. The majority of the surviving S-3As were later upgraded to the improved S-3B variant, while 16 aircraft were also converted into ES-3A Shadow electronic intelligence (ELINT) collection aircraft.

The Lockheed S-3 Viking is a conventional monoplane with a cantilever shoulder wing, very slightly swept with a leading edge angle of 15° and an almost straight trailing edge. Its twin GE TF-34 high-bypass turbofan engines mounted in nacelles under the wings provide excellent fuel efficiency, providing the Viking with the required long range and endurance, while also maintaining relatively docile engine-out characteristics.