The Grumman S2F/ S-2 Tracker was a carrier borne anti-submarine aircraft that served with the US Navy from 1954 until 1977, replacing a series of paired hunter/ killer aircraft.
In the aftermath of the Second World War the US Navy used pairs of hunter/ killer aircraft for anti-submarine warfare. Aircraft such as the Grumman AF Guardian were produced in two versions – one armed with powerful radar and the other with anti-submarine weapons. However the US Navy wasn’t happy with this system, which relied on both aircraft in the pair operating correctly to be effective. The relatively small aircraft involved in these systems were also running out of space to carry the increasingly advanced sensors needed to detect more effective post-war submarines. During the late 1940s the US Navy worked on a specification for a larger aircraft that could perform both roles.
Grumman responded with the G-89, a large twin-engine high wing monoplane. The high wing configuration was chosen to give as much space as possible in the fuselage, without wing spars coming through the middle. The engines were carried in large nacelles that also had space for expendable sonobuoys at the rear. It had a large internal weapons bay, a MAD boom in a retractable fairing at the rear, a searchlight below the starboard wing, retractable search radar in the rear fuselage. For carrier operations it had an arrestor hook and folding wings. The wings folded just beyond the engine nacelles, and the two wings folded at different angles, so when fully folded the right wing ended up in front of the left wing. The wings of all variants had a fixed wing slot on the outer wing panels, just to the rear of the wing leading edge, to improve lift.
The aircraft gained a number of names. When it first entered production it was named the Sentinel, but this had to be changed because it clashed with the Stinson L-5 Sentinel. It was then officially named the Tracker, but many of its crews called it the STOOF, taking the name from its original designation as the S-TWO-F. In the 1962 joint designation system the S2F became the S-2.
The S2F/ S-2 remained in service with the US Navy for over two decades. After entering service in 1954 it remained with the fleet until 1977, when it was finally replaced by the Lockheed S-3 Viking.
Only one S-2 was lost in combat. On 21 January 1968 an S-2D of VS-35, operating from USS Hornet, disappeared while on its way back from a night surveillance mission off the coast of Vietnam and was never found.
The S-2 was also used by Australia, Canada, Argentina, Brazil, Italy, Japan, the Netherlands, Peru, South Korea, Taiwan, Thailand, Turkey, Uriguay and Venezuela. Australia received new aircraft from Grumman, Canada built her own aircraft while the other countries all received surplus US Navy aircraft. The overseas S-2s were used from both carriers and land bases, and in some cases remained in use for much longer than in the United States. At the time of writing in 2023 the S-2 is still in use in Argentina, in an upgraded version.
On 30 June 1950 Grumman were awarded a contract to produce a prototype of the aircraft, as the XS2F-1. This aircraft made its maiden flight on 4 December 1952.
The S2F-1/ S-2A was the first production version of the aircraft. It was very similar to the prototype, but with more powerful 1,525hp Wright R-1820-82 engines. The first production aircraft made its maiden flight on 7 July 1953.
The S-2A carried AN/ APS 38 search radar with the antenna in a belly mounted radome extended 30 inches below the fuselage but could be pulled up almost into the fuselage when not in use.
It carried a nine foot long tail mounted retractable MAD boom in the tail, which was extended out behind the aircraft when in use.
Early production aircraft carried a bi-pole APA-69 ECM direction finding antenna above the cockpit. Later aircraft replaced with a radome mounted AN/ APA-69 system, carried in the same place. This system allowed the aircraft to detect passive electronic emissions from submarines.
Early aircraft carried a seventy million candlepower searchlight under the starboard wing. This was later replaced by an eighty-five million candlepower version.
The S2F-1 had an internal weapons bay and six under-wing weapon racks, three on each wing.
The weapons bay could carry a Mk 34 or Mk 43 ASW torpedo, bombs or depth charges.
The pylons could carry 5in HVAR rockers, bombs Mk 54 depth charges or 2.75in rocket pods. The inner and outer pylons on each wing could carry up to 350lb of payload, the middle pylon 265lbs.
Each of the engine nacelles could carry eight SSQ-2 sonobuoys and two larger SSQ-1 sonobuoys in tubes at the end of the nacelle. They also carried fifteen SUS (signal-underwater-sound) devices, small explosive charges that created powerful sound waves which would produce echoes that could be detected by the sonobuoys.
The S2F-1 Tracker entered fleet service with US Navy anti-submarine squadron VS 23 in 1954 for a tour of duty in the western Pacific.
A total of 755 S2F-1s were built, many of which were later converted into utility aircraft, trainers or upgraded. 625 of these aircraft were for the US Navy and 130 for export. Another 99 were built under licence in Canada as the CS2F-1/ CS2F-2 (see below).
The S2F-1T/ TS-2A was the designation given to about 200 S2F-1s that were uses as trainers. It was used in two different roles – multi-engine trainer and ASW crew trainer.
Those aircraft intended for use as multi-engine training had their ASW equipment removed and went to Training Command, where they were used by squadrons VT-27, VT-28 and VT-31 based at Corpus Christi, Texas. Pilots were given 140 hours of flight training.
Those aircraft intended for ASW crew training kept all of their equipment. They were normally armed with practice rockets and bombs on the wing racks and twenty-five Mk 15 Mod 8 practice depth charges in the weapons bay.
The TS-2A was replaced by the Beech T-44.
This version was modified to carry AQA-3 Jezebel passive long range acoustic search equipment, using with the Julie active acoustic echo ranging used small explosive charges. It used the same 1,525hp engines as the standard S2F-1. IT was a short-lived version and was soon replaced by later versions of the Tracker.
The S2F-1S1 was an upgrade to the standard S2F-1, and was given the same search equipment as the S-2E, including a more advanced version of the JULIE acoustic echo ranging system. This was the last version of the aircraft to be based on the S2F-1.
The S-2C saw the first changes to the basic design of the aircraft. It had an enlarged weapon bay, off set on the port side of the aircraft. To counter the increase in weight it had a larger tail. The larger weapons bay was designed to carry nuclear depth charges. The wing weapon pylons were strengthened, and could carry Aero 6A rocket launchers. The S2F-2/ S-2C kept the same crew, engines and internal ASW equipment as the S2F-1. Sixty were built with the first making its maiden flight on 12 July 1954. Carrier suitability trials began in April 1955 and it entered squadron service from November 1954.
These designations were given to S2Fs that were later converted into utility aircraft, for use as target tugs and light transports. In each case the internal ASW equipment, belly mounted radome, MAD boom, cockpit radome and searchlight were all removed and the sonobuoy launchers faired over.
The first version was the US-2A, based on the S2F-1. Fifty-one were converted to the new role, to replace the older C-45. They could be used as general utility aircraft, light transports, and target tugs. A number also went to the US Marines, where they were used for multi-engine proficiency flying by senior officers.
The US-2B was also based on the S2F-1, but with the space freed up by removing the ASW equipment used to create room for five passengers. Around 75 S-2As were converted to this version, with the last remaining in service until 14 October 1982.
The US-2C was based on the S2F-2/ S-2C and was mainly used as a target tug. As with the earlier utility conversions all of the ASW equipment was removed, but the sonobuoy launchers weren’t faired over. 48 of the 60 S-2Cs were converted to the US-2C and became to replace the UB-26 (JD-1) Invader as a target tug in 1964. The last US-2Cs were retired in October 1981.
The US-2D was based on the S2F-3/ S-2D. It kept the belly mounted radome although all of the internal AW equipment was removed.
A single S-2C was converted into a photographic reconnaissance aircraft at NAS Pensacola in 1964. A bulged camera compartment was installed in the rear fuselage, which could carry four cameras, two on each side. Another pair of cameras were carried below the cockpit. The RS-2C was a successful conversion, but the Navy had also developed a camera pod that would fit on the wing pylons of any S-2, so the RS-2S nvver entered production.
The S2F-3/ S-2D was the third and last major production version of the aircraft and the first to see significant changes to the airframe. In order to increase its payload it was given longer span wings and a larger tail, and more powerful R-1820-82A engines. The ECM antenna was moved from a radome over the cockpit to the new rounded wing tips. However as smaller nuclear depth charges had been developed the enlarged weapons bay of the S2F-2 was removed, so the fuselage went back to the original shape.
The extra carrying capacity was used to improve the capabilities of the aircraft. It was given extra fuel storage, increasing its endurance by more than an hour. The number of sonobuoys that could be carried was doubled. The latest versions of JULIE and JEZEBEL were installed. The under wing pyplons were strengthened, increasing the range of weapons it could carry. The interior was rearranged to increase the size of the crew compartment
The first S2F-3 made its maiden flight on 20 May 1959. This was followed by carrier trials on USS Intrepid and USS Kearsarge in the spring and summer of 1960. The first production aircraft reached the fleet on 26 October 1960, going to VS-36 at Norfolk, Virginia. A total of 100 were built, allowing the last S2F-1s to be retired by the end of 1961.
The ES-2D was an electronics warfare version of the S-2D which was given extra equipment including in some cases an extra search radar radome under the forward fuselage. Seven were converted and most were used at the Navy missile test ranges where they were used to make sure the range was clear before test shots. The last ES-2D was retired in March 1986.
The S2F-3S/ S-2E was the last production version of the aircraft built by Grumman, with 252 manufactured, of which 238 went to the US Navy and fourteen to Australia.
The main changes were to the anti-submarine warfare equipment. Externally these showed as an antenna bulge behind the retractable radome, and a long retractable blade antenna further forward.
Internally the ASA-13 plotter, navigational computer and ASA-31 Julie were all replaced by the ASM-30 Automated Tactical Navigation Equipment system, which was more effective but also heavier. The F-1 autopilot was replaced with a MA-67 autopilot which could maintain altitude and heading. New MAD gear was installed with double the range of the old system. More fuel was added, raising endurance to eight hours.
The first S-2E entered service with VS-41 in 1962 and it remained in service until the early 1970s, when it was replaced by the S-2G.
The S-2G was the last version of the aircraft to serve with the US Navy, and was produced by upgrading sixty S-2Es. The upgrade saw it given AN/ AQA-7 DIFAR processing equipment, which was used to process the data coming from sonobuoys. The same equipment was used on the P-3 Orion. The S-2G also had a three tube smoke marker ejector on the starboard engine nacelle.
The conversion kits were produced by Martin-Marietta, and installed by Navy staff at NAS Quonset Point. The first converted aircraft was delivered in December 1972 and went to VS-37 at NAS North Island, California. The same squadron then took the S-2G to sea for the first time on USS Kitty Hawk in 1973.
The S-2G was operated alongside the Lockheed S-3 Viking, to ensure that the fleet had effective ASW aircraft while the new aircraft was being introduced. As more S-3 squadrons entered service the S-2G was phased out, and the last aircraft was retired in August 1977.
TF-1/ C-1 Trader
The TF-1/ C-1 Trader was a Carrier On-board Delivery transport version
WF/ E-1 Tracer
The WF/ E-1 Tracer was an airborne early warning version of the aircraft.
In 1956 de Havilland of Canada evaluated one S2F-1 Tracker, and then paid for a licence to produce the aircraft in Canada, where it became the standard ASW aircraft of the Canadian Navy.
The CS2F-1 was externally almost identical to the American S2F-1, apart from the use of a small square ECM antenna in place of the radome carried above the cockpit on American aircraft. Internally different antenna were carried but with the same roles.
Forty four CS2F-1s were built by de Havilland Aircraft for the Canadian Navy.
The remaining 55 aircraft were produced as the CS2F-2. This version had an improved MAD system, uprated radar and improved sensors.
In 1964-67 the Canadian aircraft were given the ASN-501 tactical computer/ navigational system, APN-503 Doppler radar and improved JULIE/ JEZEBEL ASW system and re-designated as the CS2F-3.
57 improved versions
The CS2F entered service with squadron VS-881 on 7 February 1957 and VS-880 in October 1957. VS-881 was disbanded in July 1959 leaving only VS-880. The two squadrons operated the aircraft on the Canadian carrier HMCS Bonaventure. However the carrier was decommissioned in 1970, leaving the aircraft without a carrier. In 1973 their ASW equipment was removed and VS-880 became MR-880 – Maritime Reconnaissance Squadron 880. The CS2Fs, by now designated as the CP-121 under the Canadian tri-service designation system, remained in use until 1990 as coastal patrol and fishery protection aircraft. Some were retained in flying condition during the 1990s, but never returned to service.
Engine: Two Wright R-1820-82WAs
Power: 1,525hp each
Crew: 4 – 2 pilots, 2 radar operators
Span: 72ft 7in
Length: 43ft 6in
Height: 16ft 7.5in
Empty weight: 19,022lb
Gross weight: 26,867lb
Max speed: 253mph at 5,000ft
Cruising speed: 149mph at 1,500ft
Climb Rate: 1,800ft/ min
Service ceiling: 22,000ft
Range: 1,150 miles
Bomb load: up to 4,810lb: One depth charge or two torpedoes in weapons bay, six pylons under wing for depth bombs, torpedoes or rockets. Up to 32 sono-buoys in nacelles