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Aircraft carrier-based antisubmarine warfare (ASW) aircraft:

The first carrier-based ASW aircraft were central to the Battle of the Atlantic against the German U-boats of World War II. The Allies mostly used small escort carriers (CVEs) for this effort. For the U.S. Navy, this meant an aviation complement of largely torpedo bombers, although fighters were along in smaller numbers in case of German long-range aircraft attack on the escorted ships.

The torpedo bombers were Grumman TBF Avengers, designed to carry a torpedo or multiple bombs in an internal bomb bay. Later, to allow Grumman to concentrate on production of the F6F Hellcat, production of the TBF was turned over to General Motors subsidiary Eastern Aircraft and most of the torpedo bombers produced during the war were designated TBMs. Modifications for ASW were minimal to non-existent; depth charges could be loaded instead of bombs and detection of subs was by Mark 1 eyeball, and later airborne radar.

The U-boats were strictly-controlled by naval HQ and sent periodic radio updates during their patrols. This proved their undoing, as the Allies established a robust network of direction-finding sites to track the subs. In addition, code-breaking enabled the Allies to predict U-boat movements.

After the war, the U.S. Navy had thousands of surplus aircraft and converted a number of TBM-3 torpedo bombers to TBM-3S aircraft; for the first time, there was a specialized ASW aircraft.

During the war, Grumman had developed a replacement torpedo bomber: The TB3F with both R-2800 piston engine in the nose and a jet engine for combat speed. But it was clear that the era of the torpedo bomber was ending, and the TB3F was re-purposed as the Grumman AF Guardian specialized ASW aircraft and entered service around 1950 supplementing the remaining tired TBM-3S. Given the lesser need for speed, the jet was removed; the AF Guardian was the largest single-engine piston aircraft operated by the USN -- and from the smallest carrers. The Navy found that they could not fit all the required sensors and weapons into the AF and so developed two variants: The AF-2W radar plane and the AF-2S with weapons. They operated in pairs from the same escort carriers.

Clearly the team approach was not ideal; if one airplane developed engine trouble, both had to return to the carrier and land. A larger, more capable airplane was needed.

Grumman turned to the task and came up with the S2F Tracker, which became the first widely-used twin-engine carrier plane in the fleet. The S2F first flew in 1952 and quickly replaced remaining TBMs and AFs in the ASW role. At the same time, the smaller CVEs were retired from fleet duty and repurposed as aircraft transports; the S2F squadrons were embarked in full-sized fleet carriers.

As was the style during the 1950s, nuclear weapons were considered essential to Cold War operations; the S2F's internal bomb bay was too small for the initial bulky nuclear depth charge and Grumman developed a bulged weapons bay that could accommodate it. Later nuclear depth charges were more compact and the bulged bay did not last long.

The S2F served admirably during the dark blue paint era of naval aviation into the grey and white era. It remained in production into the 1960s; sort of an anachronism with its twin Wright R-1820 piston engines in a jet era Navy. In 1962, the S2F was redesigned S-2; by then the early S-2As were no longer used by ASW squadrons and the S-2D and S-2E were used by ASW squadrons.

Early S-2As served as training aircraft, towed gunnery targets for the fleet and were used for many other utility tasks. Many were also exported to other nations.

Canada undertook production of the Tracker as the CS2F (later redesignated CP-121) and even exported S2Fs to the Netherlands.

During the 1970s it became clear that a successor to the S-2 was needed. The Navy planned to upgrade their ASW carriers (former attack carriers redesigned CVS) and wanted an updated aircraft to counter Soviet submarines. The result was the Lockheed S-3 Viking, a compact twin-jet aircraft with a crew of four and chock-full of a range of ASW sensors. While the S-3 was purchased, the CVSs were retired as a post-Vietnam economy move. The S-3A ASW planes ended up being integrated into the carrier wings of already-crowded attack carriers and were often seen as second-class citizens there. The S-3s were useful for more than ASW; they were also used for buddy tankers with refueling pods on wing pylons. In fact, late in the S-3's career, the ASW equipment was removed and they were almost exclusively used as tankers. For a few years, a SIGINT version of the S-3 was also in service; it became a victim of budget cuts after the Gulf War.

Other nations developed carrier-based ASW aircraft as well. The turboprop-powered Fairey Gannet was the Royal Navy's entry. The French Navy used a somewhat similar-class Breguet Alize, also with turboprop power.

The U.S. Navy retired the S-3 in 2009 without replacement and now uses only helicopters for ship-based ASW.