* The Grumman S2F "Tracker" was one of the more prominent tools of Western naval power in the 1960s. This compact carrier-based aircraft provided a capable platform for ocean patrol and sub-hunting, and also served as the basis for the "Trader" transport and "Tracer" early-warning aircraft. This document provides a history and description of the Tracker, Trader, and Tracer.
* The Grumman company got into the antisubmarine warfare (ASW) field late in World War II, when the firm developed variants of the popular Grumman TBM Avenger torpedo bomber for that role. After the war, Grumman followed up by developing the purpose-built AF-2W and AF-2S "Guardian" carrier-based ASW aircraft. The Guardian was implemented as a pair of similar aircraft, the AF-2W "Hunter" and the AF-2S "Killer", since it proved difficult at the time to cram both functions into a single aircraft. The Guardian was a clumsy and unsatisfactory solution, and on 30 June 1950, even before the Guardian entered operational service in October 1950, the US Navy awarded Grumman a contract to develop a twin-engine carrier-based aircraft that could perform all the functions of the Guardian duo.
The contracted specified development of two prototypes of the Grumman "Model 89", with the initial military designation of "XS2F-1 Sentinel". The XS2F-1 was to carry a full complement of ASW sensors and weapons, and fly with good cruising speed over a range of up to 1,600 kilometers (1,000 miles).
The first XS2F-1 flew on 4 December 1952. It was a high-wing monoplane with a rounded, roomy fuselage, powered by twin Wright R-1820-82WA Cyclone nine-cylinder air-cooled radial engines providing 1,120 kW (1,500 HP) each, mounted in long nacelles on the wings. The XS2F-1's long wings and powerful engines allowed it to operate from small carriers and short airfields. The wings folded up hydraulically over the top of the aircraft, with the wing fold "skewed" so the two wings would overlap each other when folded. The XS2F-1 had tricycle landing gear, with twin-wheel nose gear, along with single-wheel main gear retracting backwards into the engine nacelles. The aircraft was fitted with a stinger-type arresting hook, preceded by a small tailwheel to act as a bumper on carrier landings.
The XS2F-1's ASW fit included sonobuoy ejector tubes, with eight built into the rear of each engine nacelle and firing straight out the back; a 70-million-candlepower searchlight mounted on the right wing; an AN/APS-38 search radar in a retractable ventral "dustbin" radome, behind the weapons bay; an AN/APA-69 electronics countermeasures (ECM) antenna in a teardrop fairing above the cockpit; and a retractable AN/ASQ-10 magnetic anomaly detector (MAD) boom in the tail.
The XS2F-1 carried a crew of four, with the pilot on the left, co-pilot / navigator on the right, and two systems operators in the rear. The XS2F-1 had an internal fuel capacity of 1,970 liters (520 US gallons). Total weapons load was up to 2,180 kilograms (4,800 pounds), including a single homing torpedo in the weapons bay, plus depth charges, rockets, bombs, or other stores fitted to six underwing pylons.BACK_TO_TOP
* Following trials of 15 "YS2F-1" service evaluation machines, the production "S2F-1" entered US Navy service in February 1954, with Squadron VS-26. The S2F-1 was much like the XS2F-1 prototypes, but had uprated Cyclones providing 1,138 kW (1,525 HP) each. After service introduction, the type was later renamed "Tracker". Although aircraft nicknames are something of a treacherous subject, occasionally being fabrications well after the fact, it does appear that the Tracker eventually became known as the "Stoof", a corruption of the "S-Two-F" designation.
A total of 740 S2F-1s was built by Grumman, not counting the YS2F-1 evaluation machines, with de Havilland of Canada (DHC) building an additional 43 "CS2F-1"s, with minor differences in equipment fit. The S2F-1 / CS2F-1 was built in larger quantities than all successive variants and derivatives of the type combined.
GRUMMAN S2F-1 TRACKER: _____________________ _________________ _______________________ spec metric english _____________________ _________________ _______________________ wingspan 21.23 meters 69 feet 8 inches length 12.88 meters 42 feet 3 inches height 4.95 meters 16 feet 3 inches empty weight 8,310 kilograms 18,315 pounds max loaded weight 11,900 kilograms 26,300 pounds maximum speed 462 KPH 287 MPH / 250 KT service ceiling 6,710 meters 22,000 feet range 1,350 kilometers 840 MI / 730 NMI _____________________ _________________ _______________________
* The US Navy relied heavily on the Tracker for fleet defense, and took measures to keep the type up to date. Many USN Trackers were retrofitted with the AN/AQA-3 "Jezebel" acoustic search (passive sonar) and "Julie" echo-ranging (active sonar) gear, and redesignated "S2F-1S". The Julie system involved fitting ejector tubes for echo-sounding explosive charges in the bottom of the rear fuselage.
The next production model, the "S2F-2", featured a protruding and offset weapons bay to accommodate an oversized nuclear depth charge, plus an enlarged tailplane to compensate for the resulting aerodynamic changes. The swollen weapons bay gave the S2F-2 a slightly pregnant look. A total of 77 S2F-2s was built by Grumman, with an additional 57 similar "CS2F-2" machines built by DHC.
* The "G-121 / S2F-3" first flew on 21 May 1959, and featured a fuselage stretch of 46 centimeters (1 foot six inches), a still larger tailplane, and an increase in wingspan of 89 centimeters (2 feet 11 inches). The S2F-3 was bigger overall to provide more crew space, fuel capacity, and equipment load. The S2F-3 entered fleet service in May 1961.
Since smaller nuclear depth charges had been developed, the weapons bay was shrunk back to its original size. The ECM antenna fairing on top of the cockpit was removed, replaced by an improved ECM system using antennas fitted into the wingtips, and most of the other electronics systems were modernized as well. Stores pylons were strengthened, and the sonobuoy compartments at the end of the nacelles were noticeably enlarged to increase sonobuoy capacity from 8 to 16 in each nacelle. 100 S2F-3s were built in all.
GRUMMAN S2F-3 TRACKER: _____________________ _________________ _______________________ spec metric english _____________________ _________________ _______________________ wingspan 22.12 meters 72 feet 7 inches wing area 46.08 sq_meters 496 sq_feet length 13.26 meters 43 feet 6 inches height 5.05 meters 16 feet 7 inches empty weight 8,500 kilograms 18,750 pounds max loaded weight 13,220 kilograms 29,150 pounds maximum speed 426 KPH 265 MPH / 230 KT service ceiling 6,400 meters 21,000 feet range 2,090 kilometers 1,300 MI / 1,130 NMI endurance 9 hours _____________________ _________________ _______________________
The final production variant of the Tracker was the "S2F-3S", essentially an S2F-3 with Julie-Jezebel gear and a TACAN radio navigation beacon receiver system. The last of 252 S2F-3s was delivered in 1968, and were the last of a total of 1,284 Trackers built in the US and Canada.
A number of S2F-3S Trackers were later fitted with AN/AQA-7 sonobuoy processing gear and redesignated "S-2F", and apparently many S2F-1S aircraft were updated to the same or similar specification and given the same S-2F designation. There was also an upgrade of 50 S2F-3S machines with the designation "S-2G" to allow it to carry a pair of AGM-12 "Bullpup" radio-guided air-to-surface missiles. The copilot guided them using a joystick and watching a flare on the tail of the missile.
* A total of 20 US Navy squadrons was ultimately equipped with the Tracker. The type also did very well on the international market, with help from the US Military Assistance Program, being supplied to Argentina, Australia, Brazil, France, Italy, Japan, the Netherlands, Taiwan, Thailand, Turkey, and Uruguay.BACK_TO_TOP
* With such a large number of Trackers built, it wasn't surprising that many airframes were modified for other purposes:
When the US military consolidated aircraft designation schemes in 1962, the different Tracker variants were redesignated as follows:
________________ S2F-1: S-2A S2F-1T: TS-2A S2F-1S: S-2B S2F-2: S-2C S2F-2P: RS-2C S2F-2U: US-2C S2F-3: S-2D S2F-3U: US-2D S2F-3S: S-2E ________________
Canadian Trackers were given a service-life update in the mid-1960s, with substantial system updates, and redesignated "CP-121" when the Canadian Armed Forces were created by service consolidation in early 1968.
* The Tracker served with the US Navy with quiet distinction during the 1960s. Along with its primary role to protect the fleet from Soviet submarines, it was used for maritime patrol during the Vietnam War, assisting in rescues of aircrew downed at sea and occasionally engaging North Vietnamese patrol boats using unguided rockets, fired from underwing pods. One Tracker was lost to enemy action. Its non-combat losses were also low, and in fact the Tracker had an enviable safety record.BACK_TO_TOP
* The Tracker was replaced by the Lockheed S-3 Viking in first-line operation in the 1970s, and the last operational Tracker, an ES-2D, was phased out in the mid-1980s. The type remained in use with a number of international air arms for much longer. Although it was obsolete in the ASW role by the time it ended production, it was still an effective aircraft for maritime patrol to monitor surface shipping, and at last notice was still being operated in declining numbers in this role by various countries.
It also remains in use as a popular "water bomber" to fight forest fires, with Trackers modified to carry 3,032 liters (800 US gallons) of fire retardant. One of the primary users is the California Department of Forestry (CDF), but other Tracker water bomber conversions have been performed for Canada and Turkey. Although the Tracker is a capable and rugged aircraft, its stubby fuselage does make it difficult to handle in turbulence, particularly after retardant release, and a number of CDF pilots have lost their lives in crashes.
Maintaining the old Wright Cyclones is becoming increasingly difficult, and so "Turbo Tracker" conversions have become popular. The engines of choice are the Garrett TPE331 or the Pratt & Whitney Canada (PWC) PT6A turboprop, both typically rated at 1,225 kW (1,645 SHP), and conversions have been performed by a number of companies:
Although most Trackers are far from the end of their airframe lives, a tribute to the traditional ruggedness of Grumman designs, military Turbo Tracker conversions have not been as popular as expected. Older versions of the P-3 Orion are now available on the international used-aircraft market, and buyers prefer the more capacious and longer-legged Orion over the Tracker.BACK_TO_TOP
* In 1955, Grumman flew the prototype of the "G-96 / TF-1 Trader" "carrier onboard delivery" (COD) derivative of the Tracker. The Trader featured a modified fuselage, but was otherwise parts-compatible with the Tracker. The Trader could be fitted with easily-removed seats for nine passengers, and included front and rear sliding bulkheads mounted on rails, plus removeable posts, to secure cargo for carrier landings. Maximum cargo capacity was 3,855 kilograms (8,500 pounds). Life rafts were fitted into the rear of the engine nacelles.
First flight of the Trader was in January 1955, with initial service delivery in 1957. A total of 87 was built from 1955 into 1958, including four fitted for the ECM role and given the designation "TF-1Q". In 1962, the TF-1 was given the new designation of "C-1A", and the TF-1Q was redesignated "EC-1A". The Trader served with three US Navy logistics support and transport squadrons, but it was strictly an interim type, being replaced by the Grumman C-2 Greyhound.
Some Traders ended up in civilian hands, and in 2010 the Brazilian Navy bought eight C-1As for use in the COD and tanker roles on the carrier SAO PAULO -- these machines apparently having been obtained from mothballed aircraft. They were refurbished and reengined with Honeywell TPE331 turboprops driving five-bladed props.BACK_TO_TOP
* The Trader led in turn to another Tracker derivative, the "G-117 / WF-2 Tracer" airborne early-warning (AEW) variant. The Tracer started life as a proposal to the Navy in 1951 for the "XWF-1", resulting in a contract for two prototypes of an AEW machine based on the Tracker -- but all that was built was a partial mockup, the program being canceled in 1953. The program was revived in 1955, with Grumman proposing an AEW aircraft based on the Trader instead of the Tracker. A Trader was used as an aerodynamic prototype, performing its initial flight on 17 December 1956. The first production WF-2 performed its initial flight on 1 March 1958, with a total of 88 built into 1961.
The Tracer featured a large dorsal "saucer" radome made of honeycomb fiberglass, with dimensions of 6.1 by 9.14 meters (20 by 30 feet), to accommodate the antenna for its Hazeltine AN/APS-82 search radar, and a new tail unit with three tailfins to compensate for the wake interference of the radome. Since the radome blocked the wings from folding upward, they were redesigned to fold backward along the fuselage in classic Grumman fashion. The aircraft also featured a identification friend or foe (IFF) interrogator to determine if targets were friendly or hostile, plus a "Bellhop" system to transfer radar data to a surface vessel, and a communications relay transponder. The Tracer had a crew of four, including pilot, copilot, and two radar operators. It was known as "Willie Fudd" by crews, in reference to its designation code, and sometimes as "Stoof With A Roof".
GRUMMAN WF-2 TRACER: _____________________ _________________ _______________________ spec metric english _____________________ _________________ _______________________ wingspan 22.12 meters 72 feet 7 inches wing area 46.08 sq_meters 496.0 sq_feet length 13.82 meters 45 feet 4 inches height 5.13 meters 16 feet 10 inches empty weight 9,535 kilograms 21,025 pounds max loaded weight 12,230 kilograms 26,970 pounds _____________________ _________________ _______________________
The WF-2 was redesignated "E-1B" in 1962. Like the Trader, the Tracer was an interim type, being replaced by the Grumman E-2 Hawkeye from the late 1960s, with the last Willie Fudd retired in 1977.
* The following table gives Tracker / Trader / Tracer variants and production quantities:
variant built mod notes ____________________________________________________________________ XS2F-1 2 Initial prototypes. YS2F-1 15 Service evaluation machines. S2F-1 (S-2A) 740 Initial & main production variant. CS2F-1 43 DHC-built S2F-1. S2F-1S (S-2B) - ? S2F-1 with improved ASW kit. S2F-2 (S-2C) 77 Bulged bombbay for nuke depth charges. CS2F-2 57 DHC-built S2F-2. S2F-3 (S-2D) 100 "Stretched" Tracker. S2F-3S (S-2E) 255 S2F-3 with improved ASW kit. S-2F - ? S2F-1 & S2F-3S with new avionics. S2F-1T (TS-2A) - 200 S2F-1 multi-engine trainer. US-2A - 51 S2F-1 transport / target tug. US-2B - 75 S2F-1 utility aircraft. S2F-2P (RS-2C) - 1 S2F-2 photo-reconnaissance conversion. S2F-2U (US-2C) - ? S2F-2 transport conversions. S2F-3U (US-2D) - 54 S2F-3 transport conversions. ES-2D - 7 S2F-3 range control conversions. S-2G - 50 S2F-3S with Bullpup ASM capability. CP-121 - ? Canadian Tracker updates. ____________________________________________________________________ sum 1,289 ____________________________________________________________________ TF-1 (C-1A) 83 Trader COD aircraft. TF-1Q (EC-1A) 4 Trader EW aircraft. ____________________________________________________________________ sum 87 ____________________________________________________________________ WF-1 1 Tracer AEW prototype. WF-2 (E-1B) 88 Production Tracer. ____________________________________________________________________ sum 89 ____________________________________________________________________ TOTAL 1,465 ____________________________________________________________________
As usual, there may be minor discrepancies in this count, but it can be regarded as well in the ballpark.BACK_TO_TOP
* One of the might-have-beens of the Tracker story was consideration of its use as a gunship in Vietnam. The idea wasn't ridiculous, the Lockheed P2V Neptune having seen some use as a "jungle fighter" in the conflict. The Air Force was looking for a "Self Contained Night Attack (SNCA)" platform that could locate targets on its own at night and engage them; the Tracker seemed to have the payload capability to do the job.
The gunship Tracker was to be designated the "AS-2D". It was to be fitted with "forward looking infrared (FLIR)" and "low light level TV (LLLTV)" sensors to obtain targets, with the Tracker's standard searchlight slaved to the LLLTV. Weapons were to consist of cluster munitions dispensers in the bombbay and stores carried on the underwing pylons. Two "YAS-2D" evaluation machines were planned, but the effort ran into technical and organizational difficulties, with the Air Force pulling the plug on the exercise in early 1968.
* Sources include:
The "S-2F Tracker" website in the Netherlands was a significant source of information as well, and some minor details were obtained from the 1960 edition of JANE'S ALL THE WORLD AIRCRAFT. The information on Brazilian Trackers was provided by Captain Marcio Jansen Calvacanti of the Brazilian Navy.
* Revision history:
v1.0 / 01 mar 01 v1.0.1 / 01 jan 02 / Review & polish. v1.0.2 / 01 jan 04 / Review & polish. v1.0.3 / 01 jan 06 / Review & polish. v1.0.4 / 01 dec 07 / Review & polish. v1.0.5 / 01 jun 09 / AS-2D gunship comments. v1.0.6 / 01 may 11 / Review & polish. v1.0.7 / 01 apr 13 / Brazilian Traders.BACK_TO_TOP