The Grumman S-2 Tracker (S2F prior to 1962) is the first purpose-built, single airframe anti-submarine warfare (ASW) aircraft to enter service with the United States Navy. Designed and initially built by Grumman, the Tracker was of conventional design — propeller-driven with twin radial engines, a high wing that could be folded for storage on aircraft carriers, and tricycle undercarriage. The type was exported to a number of navies around the world. Introduced in 1952, the Tracker and its E-1 Tracer derivative saw service in the U.S. Navy until the mid-1970s, and its C-1 Trader derivative until the mid-1980s, with a few aircraft remaining in service with other air arms into the 21st century. Argentina was the last country to operate the Tracker, with the last two Trackers being taken out of service on 19 November 2025.
Design and development
The Tracker was intended as a replacement for the Grumman AF Guardian,Francillon 1989, p. 351 which was the first purpose-built aircraft system for anti-submarine warfare. The Guardian operated in two aircraft "hunter-killer" pairs, with one aircraft (the AF2-W) carrying the detection gear to find the submarine and to direct the second aircraft, the AF-2S, which carried weapons to attack and destroy the submarine.Sullivan 1990, p. 4 The Tracker combined both functions in one aircraft, saving deck space aboard carriers and making for more efficient operations. Grumman's design (model G-89) was for a large high-wing monoplane with twin Wright Cyclone R-1820 nine cylinder radial engines, a yoke type arrestor hook and a crew of four. Both the two XS2F-1 prototypes and 15 S2F-1 production aircraft were ordered at the same time, on 30 June 1950. The first flight was conducted on 4 December 1952, and production aircraft entered service with VS-26, in February 1954.
Follow-on versions included the WF Tracer and TF Trader, which became the Grumman E-1 Tracer and Grumman C-1 Trader in the tri-service designation standardization of 1962. The S-2 carried the nickname "Stoof" (S-two-F) throughout its military career; and the E-1 Tracer variant with the large overhead radome was colloquially called the "stoof with a roof.".O'Rourke, G.G., Captain USN. "Of Hosenoses, Stoofs, and Lefthanded Spads". United States Naval Institute Proceedings, July 1968.
Grumman produced 1,185 Trackers and another 99 aircraft carrying the CS2F designation were manufactured in Canada under license by de Havilland Canada. U.S.-built versions of the Tracker were sold to various nations, including Australia, Japan, Turkey and Taiwan.
Sensors and armament
The Tracker had an internal torpedo bay capable of carrying two lightweight aerial torpedoes or one nuclear depth charge. There were six underwing hard points for rocket pods and conventional depth charges or up to four additional torpedoes. A ventrally-mounted retractable radome for AN/APS-38 radar and a Magnetic Anomaly Detector (MAD) AN/ASQ-8 mounted on an extendable rear mounted boom were also fitted. Early model Trackers had an Electronic Support Measures (ESM) pod mounted dorsally just aft of the front seat overhead hatches and were also fitted with a smoke particle detector or "sniffer" for detecting exhaust particles from diesel-electric submarines running on snorkel. Later S-2s had the sniffer removed and had the ESM antennae moved to four rounded extensions on the wingtips. A 70-million-candlepower searchlight was mounted on the starboard wing. The engine nacelles carried JEZEBEL sonobuoys in the rear (16 in early marks, 32 in the S-2E/G). Early Trackers also carried 60 explosive charges, dispensed ventrally from the rear of the fuselage and used to create sound pulses for semi-active sonar (JULIE) with the AN/AQA-3 and later AQA-4 detection sets, whereas the introduction of active sonobuoys (pingers) and AN/AQA-7 with the S-2G conversion saw these removed. Smoke dispensers were mounted on the port ventral surface of the nacelles in groups of three each.
Operational history
The Tracker was eventually superseded in U.S. military service by the Lockheed S-3 Viking; the last USN Tracker operational squadron (VS-37 with S-2G models) was disestablished in 1976. The last Navy S-2 was withdrawn from service on 29 August 1976."The Seventies." history.navy.mil. Retrieved: 15 June 2010. For many years the TS-2A version of the Tracker was used by U.S. Navy training units, culminating with its use by Training Squadron 27 (VT-27), Training Squadron 28 (VT-28) and Training Squadron 31 (VT-31) for Student Naval Aviator training in the multi-engine pipeline with Training Air Wing FOUR (TRAWING 4) at Naval Air Station Corpus Christi, Texas.
A number of Trackers live on as firefighting aircraft while the design also continued to provide excellent service with the naval forces of other countries for years after the U.S. retired them. For example, the Royal Australian Navy continued to use Trackers as front line ASW assets until the mid-1980s.
Argentina
Argentine Naval Aviation received seven S-2As in 1962, six S-2Es in 1978, and three S-2Gs in the 1990s. They were operated from both aircraft carriers, and , and used in the carrier onboard delivery (COD) (US-2A conversions,Jackson, David D. "Grumman S2F / S-2 Trackers in service with the Argentina Navy." Surviving Grumman S2F Tracker Information Repository, 2010. Retrieved: 15 June 2010.) maritime patrol, and ASW roles. They were extensively used in the 1982 Falklands War, first from ARA Veinticinco de Mayo, from where they detected the British task force on 1 May 1982 in the failed naval strike attempt carried by Argentinean Naval forces, and then from the mainland institutoaeronaval.org. Retrieved: 15 June 2010. when the carrier returned to port after the sinking of the cruiser , During that trip back to port the S-2E carried ASW sorties including the attack of submarine contacts with aerial torpedoes. In the 1990s, six remaining airframes were refurbished by Israel Aerospace Industries with turboprop engines as S-2T Turbo Trackers. with the retirement of Argentina's only aircraft carrier, the Trackers were deployed on board Brazilian Navy aircraft carrier . and with U.S. Navy aircraft carriers during Gringo-Gaucho maneuvers."S-2 video." youtube.com. Retrieved: 15 June 2010. at least one S-2T was reported still operational in the maritime surveillance role. The last Argentine S-2T was formally retired on 1 December 2025.
Australia
Between 1967 and 1984 the Royal Australian Navy operated two Squadrons of S-2E and S-2G variants, based at NAS Nowra ().Gillett 1987, p. 206. These aircraft served with the RAN's 816 Squadron, which embarked aboard the as part of the 21st Carrier Air Group whenever that ship was deployed; and with 851 Squadron, the S-2 training squadron.
Australia initially acquired 14 S-2Es. During approximately 17 years of operation of the Tracker, the RAN lost only one S-2 during aircraft operations due to an accident at sea on 10 February 1975. However, on 4 December 1976, a deliberately lit fire in a hangar at Nowra destroyed or badly damaged a large proportion of the RAN's complement of Trackers. Of the 14 original aircraft, one was away from Nowra undergoing maintenance at the time of the fire and three aircraft were damaged but only two of these were repaired. The destroyed aircraft were subsequently replaced with 16 ex-USN aircraft. The replacement aircraft were all S-2Gs, including the original aircraft modified by the USN to that status.Francillon 1989, p. 367. This saw the introduction of AQA-7 acoustic gear into RAN service and all RAN operational Trackers were subsequently modified to this standard.
Brazil The Brazilian Air Force flew Trackers from the aircraft carrier NAeL . Both the S-2A and S-2E were used (respectively as P-16A and P-16E). At the end of its service in Brazilian Air Force, one S-2T Turbo Tracker was evaluated as a possible upgrade, but due high costs the program was canceled. However, in 2010 the Brazilian Navy contracted Marsh Aviation to convert four S-2Ts to Airborne Early Warning configuration and upgrade four additional Grumman C-1 Traders for tanking and carrier onboard delivery transport duties. The latter were scheduled to be back in service by 2015 and were expected to operate from the successor of Minas Gerais, NAe São Paulo."Brazilian Traders set for modernisation." flightglobal.com, 14 December 2011 Retrieved: 23 December 2011 Following the bankruptcy of Marsh Aviation in 2009 the program suffered delays and the upgrade of the airframes was resumed in partnership with Elbit Systems's subsidiary, M7 Aerospace. The decommissioning of the São Paulo in 2017 means that the Brazilian Navy does not have an immediate need for carrier-based tankers, transports and AEW aircraft, however the navy proceeded with procurement and the delivery of four tanker aircraft are expected by 2021.
As noted under Argentina above, Trackers of that country have been flown from the São Paulo until its decommissioning in early 2017.
Canada
In 1954, de Havilland Canada (DHC) entered into a contract to build 100 Trackers under license to replace the outmoded Grumman TBM-3E Avengers being used by the Royal Canadian Navy (RCN). 99 Trackers were actually built by DHC, with the first Canadian-built aircraft flying on 31 May 1956. From 1957 onwards, these aircraft operated from the newly deployed aircraft carrier and various shore bases.Cummings 1988, pp. 180–182. All the Canadian Trackers were built to the earlier "A" model airframe design with a length of Taylor 1987 (cf. for later model Trackers) in order to fit in Bonaventures hangar."de Haviland Grumman CP-121 Tracker." airforce.forces.gc.ca. Retrieved: 19 November 2012. In 1960–1961, 17 CS2F-1 aircraft, which had been relegated to training and utility duties by the CS2F-2, were transferred to the Royal Netherlands Navy. From 1964, 45 CS2F-2s were upgraded by fitting revised electronic equipment and sensors, becoming CS2F-3s. Also in 1964, a pair of CS2F-1 aircraft were stripped of armament and ASW electronics, converted to transports, and subsequently used for carrier onboard delivery.Cummings 1988, p. 182. The CS2F-1, -2, and -3 were redesignated as the CP-121 Mk.1, Mk. 2, and Mk. 3 respectively following the unification of Canadian forces in 1968.
After Bonaventure was decommissioned in 1970, all remaining Canadian Trackers were transferred to shore bases. This limited their usefulness for ASW patrols, and between 1974 and 1981 gradually all but 20 were placed in storage and the remainder were stripped of their ASW gear. The remaining active-duty Trackers served until 1990 on fisheries protection and maritime patrol duties. A handful of Trackers were kept in flying condition until the late 1990s but were no longer used for active service.Tate, Colonel D.H. "Grumman CS2F / CP-121 Tracker." Canada Aviation and Space Museum. Retrieved: 22 March 2009.
DHC purchased a single U.S.-built S2F-1 from Grumman for testing avionics and anti-submarine systems and also for evaluating Engineering Change Proposals created by Grumman; it was initially given RCN serial number 1500 and counted as one of the 100 contracted airframes. In 1954, this aircraft was transferred to the RCN for operational testing, and assigned the test code X-500. In 1956, it was upgraded to CS2F-1 standards and assigned serial number 1501; it was last used as a stationary instructional airframe at Shearwater until 1972. It is not known whether this aircraft was ever assigned a U.S. Navy bureau number.
Japan