Saab 37 Viggen

The Saab 37 Viggen (Swedish: "(thunder)bolt") was a Swedish single-seat, single-engine, short-medium range fighter and attack aircraft, manufactured between 1970 and 1990. Several variants were produced to perform the roles of all-weather fighter-interceptor, ground-attack and photo-reconnaissance, as well as a two-seat trainer.

Development
The Viggen was initially developed as a replacement for the Saab 32 Lansen in the attack role and later the Saab 35 Draken as a fighter. The first studies were carried out between 1952 and 1957 involving the Finnish aircraft designer Aarne Lakomaa. Several different concepts were studied involving both single- and twin engines and also with separate lift engines, both simple and double delta wings and also with canard wings. Even VTOL designs were considered.



The aim was to produce a robust aircraft with good short-runway performance that could be operated from numerous specially prepared roads and highways to reduce the vulnerability to attack in the event of war. Other requirements included supersonic ability at low level, Mach 2 performance at altitude, and the ability to make short landings at low angles of attack (to avoid damaging improvised runways). The aircraft was also designed from the beginning to be easy to repair and service, even for personnel without much training.

To meet these design goals, Saab selected a radical configuration: a conventional delta wing with a small, high-set canard foreplane. Canard aircraft have since become common in fighter aircraft, notably with the Eurofighter Typhoon, Dassault Rafale, Saab JAS 39 Gripen and the IAI Kfir, but mainly for agility reasons rather than STOL capabilities. The final proposal was presented and accepted on 28 September 1962. Construction started in 1964, with a first prototype maiden flight on 8 February 1967.

In 1960, the U.S. National Security Council, led by President Eisenhower, formulated a military security guarantee for Sweden. The U.S. promised to help the Swedish militarily in the event of a Soviet attack against Sweden; both countries signed a military-technology agreement. In what was known as the "37-annex", Sweden was allowed access to advanced U.S. aeronautical technology which made it possible to design and produce the Saab 37 Viggen much faster and cheaper than would otherwise have been possible.

According to the licensiate research of Nils Bruzelius at the Swedish National Defence College, the reason for this officially unexplained U.S. support was the need to protect U.S. Polaris submarines deployed just outside the Swedish west coast against the threat of Soviet anti-submarine aircraft.

However, Bruzelius' theory has been criticized by Simon Moores and Jerker Widén.

Propulsion
The Viggen was powered by a single Volvo RM 8 turbofan. This was essentially a licence-built variant of the Pratt & Whitney JT8D engine that powered commercial airliners of the 1960s, with an afterburner added for the Viggen. The airframe also incorporated a thrust-reverser to use during landings and land manoeuvres, which, combined with the aircraft having flight capabilities approaching a limited STOL-like performance, enabled operations from 500 m airstrips with minimal support. The thrust reverser could be pre-selected in the air to engage when the nose-wheel strut was compressed after touchdown. The Viggen was the first aircraft to feature both afterburners and thrust-reversers. Only the Viggen, Concorde and the Panavia Tornado featured both afterburners and thrust-reversers.



The requirements from the Swedish Air Force dictated Mach 2 capability at high altitude and Mach 1 at low altitude. At the same time, short-field takeoff and landing performance was also required. Since the Viggen was developed initially as an attack aircraft instead of an interceptor (the Saab 35 Draken fulfilled this role), some emphasis was given to low fuel consumption at high subsonic speeds at low level for good range. With turbofan engines just emerging and indicating better fuel economy for cruise than turbojet engines, the former was favoured, since the latter were mainly limited by metallurgy development resulting from limitations in turbine temperature. Mechanical simplicity was also favoured, so the air intakes were simple D-section types with boundary layer splitter plates, while the fixed inlet had no adjustable geometry for improved pressure recovery. The disadvantage was that the required engine would be very large. In fact, at the time of introduction, it was the second largest fighter engine, with a length of 6.1 m and 1.35 m diameter; only the Tumansky R-15 was bigger.

Saab had originally wanted the Pratt & Whitney TF30 as the Viggen's powerplant. Since the engine design had not been completed in 1962 when the airframe vs. engine design size needed to be frozen, the JT8D was chosen as the basis for modification instead. The RM 8 became the second operational afterburning turbofan in the world, and also the first equipped with a thrust reverser. It had a bypass ratio of around 1.07:1 in the RM 8A, which reduced to 0.97:1 in the RM 8B.

The AJ, SF, SH and SK 37 models of the Viggen had the first version of the RM 8A engine with uprated internal components from the JT8D that it was based on. Thrust was 65.6 kN dry and 115.6 kN with afterburner. For the JA 37, the RM 8A was modified to an 8B by replacing one LP compressor stage with a fan stage and improved combustor, turbine and afterburner. Thrust is 72.1 kN dry and 125.0 kN with afterburner. The engine was started via a small gas turbine, itself started by an electric motor. Standby power and cooling air for onboard avionics were supplied via an external cart. An internal battery permitted start of the starter turbine and main engine in absence of the standby power cart.

Avionics
In the early 1960s, it was decided that the Viggen should be a single seat aircraft. A digital central computer and a head-up display replaced the human navigator. The computer, called CK 37 (centralkalkylator 37), was the world's first airborne computer to use integrated circuits. It utilized the STRIL 60 system to link with Swedish defence systems. The main sensor was an Ericsson PS 37 X-band monopulse radar with several functions, including air-to-ground and air-to-air telemetry and cartography. A Honeywell radar altimeter with transmitter and receiver in the canard wings was used to assist low altitude flight. The aircraft also used a Decca Type 72 doppler navigation radar. TILS (Tactical Instrument Landing System), a landing-aid system made by Cutler-Hammer AIL, improved landing accuracy to 30 m from the threshold on the short highway airbase system. ECM consisted of a Satt Elektronik radar warning receiver system in the wings and the tail, an optional Ericsson Erijammer pod and BOZ-100 chaff/flare pod. In total, the electronics weighed 600 kg, a substantial amount for a single-engine fighter of the era.

The SK 37 trainer omitted the radar and CK 37 navigational computer, navigating only using the Decca system and later DME. The radar warning receiver electronics were also removed.

Initially, only a single reconnaissance (S) variant was considered, but fitting cameras as well as a radar proved to be impossible. The SH 37 maritime strike and reconnaissance variant was very similar to the AJ 37 and differed mainly in a maritime optimized PS 371/A radar with longer range and cockpit camera and tape recorder for mission analysis. "Red Baron" and LOROP camera pods were usually carried on the fuselage pylons. The centerline fuel tank was converted for a short period of time to a camera pod with two Recon/Optical CA-200 1676 mm cameras. In addition to the reconnaissance equipment, the SH 37 could also use all weapons for the AJ 37. For the photographic SF version, the radar in the nose was omitted in favour of one SKa 24 57 mm, three SKa 24C 120 mm and two SKa 31 600 mm photographic cameras as well as one VKa 702 Infrared linescan camera. The "Red Baron" and LOROP camera pods could also be carried on the fuselage pylons.

The avionics suite of the JA was a major improvement over the other variants designed a decade earlier. The onboard computer was a Singer-Kearfott SKC-2037 built under license by Saab as CD 107, a Garrett AiResearch LD-5 air data computer (also used in the Grumman F-14 Tomcat), a Saab-Honeywell SA07 automatic flight control systems (which was the first digital variant to enter production) and a KTL-70L inertial navigation system. In the cockpit, several dial-indicator instruments were replaced by two CRT displays; one target indicator MI (sw: MålIndikator) in the center and one tactical moving- and rotating map indicator TI (sw: Taktisk Indikator) to the right while the head-up display SI  (sw: SiktlinjesIndikator - line-of-sight indicator) was retained.

The radar on the JA 37 was upgraded to a multi-mode, pulse-Doppler Ericsson PS 46/A unit more optimized for the fighter/interceptor role. It sported lookdown/shootdown capability, range up to 48 km, continuous-wave illumination for the Skyflash missiles as well as the ability to track two targets while scanning. The MTBF was reported as 100 hours, a very high reliability level for that generation of avionics systems.

In 1992, an upgrade program of some of the AJ/SF/SH (with least hours on the airframe) to AJS/AJSF/AJSH was initiated because of delays of the new JAS 39 Gripen. The modifications were not too extensive and consisted to the major part of a new Ericsson computer processor system, MIL-STD-1553B databus and MIL-STD-1760 stores interface system to carry the Rb 15F anti-ship missile and DWS 39 Mjölner submunitions dispenser. An upgraded radar warning receiver system with recording capability as well as a Mission planning system via a portable cartridge were also implemented. The original PS 37/A radar from the AJ 37 was upgraded to the PS 371/A (from the SH 37) allowing the new AJS 37 to perform radar reconnaissance missions. No airframe- and very minor cockpit modifications were made.

The JA 37 was continuously upgraded throughout its lifetime. In 1985, the "fighter link" went into service, permitting encrypted data communication between four fighters. This enabled one fighter to "paint" an airborne enemy with guidance radar for the Skyflash missiles of the three other fighters in a group while they had their search and guidance radar switched off. This system was operational 10 years before any other country's. The autopilot was also slaved to the radar control to obtain better precision firing the cannon.

In 1990, the PS 46/A was upgraded with higher resistance to jamming and the ability to track several targets at the same time. In 1993, the ability to generate virtual targets in the radar reduced the cost of flying aggressors for training.

Between 1992 and 1997, a major avionics upgrade program to the JA was implemented, given the new designation JA 37D. It consisted of an Ericsson CD207 mission computer, an ANP-37 stores management computer, linked via dual MIL-STD-1553B databuses permitting use of the RB 99 AMRAAM. In the cockpit, a TI 327 color tactical moving-map display (originally intended for the Gripen) and a Synthetic Attitude Heading Reference System were installed. The ECM and ECCM suite were enhanced with improved electronics, upgraded radar warning receivers, a new Ericsson U95 jammer pod as well as the ability to carry BOY-401 chaff/flare dispensers on a separate location from the weapon pylons.

Between 1998 and 2000, the conversion of 10 SK 37 trainers to SK 37E electronic aggressors was completed. The fairly substantial upgrade package consisted of the nose-radome mounted G24 jammer inherited from the decommissioned J 32E Lansen, U22/A jammer- and KB chaff/flare pods and radar warning receivers from the AJS 37 and a new U95 jammer pod all linked together with the MIL-STD-1553B databus. The rear cockpit for the Electronic Warfare Officer was improved with new displays and controls while retaining the ability to convert back to the original flight training role.

Cockpit
The displays in the original cockpit were all of the traditional analogue/mechanical type with the exception of an electronic HUD which could be used as a precision landing aid. Original layout drawings show the forward display area dominated by a central large Horizontal Situation Indicator (HSI) with its integral altitude warning light. To the left were the attitude indicator, altimeter and airspeed indicator / MACH displays and to the right, twelve smaller displays including a clock, g-meter, destination indicator, standby instruments, R.P.M. indicator, distance indicator, EPR indicator and fuel indicator.

The ejection seat was the Raketstol 37 (literally; Rocket chair 37) and was the last Saab designed seat in service. A derivative of the Saab 105 trainer seat, the seat was optimized for low altitude, high speed ejections. Low speed capability was limited (on the first versions of the rocket chair) to speeds above 75 km/h on the runway. The seat was angled back by 19 degrees to help counter g-forces in flight. The generation 3 of the rocket chair had zero-zero capability, meaning it needed zero forward speed and zero altitude. The pilot flew with a centre stick and left side throttle. The hands-on-throttle–and-stick HOTAS controls included trim, autopilot disengage, event marker and trigger (on the stick) and ECM switch and missile seeker un-cage (on the throttle). Adjacent to the throttle was a separate radar joystick.

There were dedicated warning caption panels each side of the pilot's legs. On the right console panel were numerous dedicated controls and indicators, including weapons and missile controls, nav panel, oxygen on/off, windshield de-fogging, IFF control, lighting controls. Situated on the left console panel were radar controls, canopy handle, landing gear handle, radio controls and the cabin pressure indicator. A detailed schematic diagram of the original cockpit layout may be found in "Control in the Sky" by L.F.E. Coombs. Photographs of the original cockpit may be found at:

Wings and airframe
With the performance requirements to a large extent dictating the choice of the engine, the airframe turned out to be quite bulky compared to contemporary slimmer designs with turbojet engines. The first prototypes had a straight midsection fuselage that was later improved with a "hump" on the dorsal spine for reduced drag according to the area rule. The wing had the shape of a double delta with a dogtooth added to improve longitudinal stability at high incidence angles. Each dogtooth was also used as a fairing for a radar warning receiver (RWR) antenna.

A consequence of a tailless delta design, such as in the Viggen, is that the elevons, which replace more conventional control surfaces, operate with a small effective moment arm; their use adds substantial weight to the aircraft at takeoff and landing. Hinged leading edge surfaces can help counteract this, but an even more effective tool is the canard. The canard surfaces were positioned behind the inlets and placed slightly higher than the main wing, with a higher calage that the wing, and were equipped with flaps. The lifting canard surfaces act also as a vortex generator for the main wing and therefore provide more lift. An added benefit was that they also improved roll stability in the transonic region around Mach 0.9. The canard flaps were deployed in conjunction with the landing gear to provide even more lift for takeoff and landing.

To withstand the stresses of no-flare landings, Saab made extensive use of titanium in the construction of the Viggen, especially in the fuselage, and incorporated an unusual arrangement for the main landing gear, in which the two wheels on each leg were placed in tandem. While such a layout is common in airliners and cargo aircraft, it is rare in fighters, but allows stowage in a thinner wing. The tall single vertical stabilizer (45 degrees sweepback on the leading edge) was foldable to make it easier to store in hangars. After prototype testing of the SK variant, reduced longitudinal stability was discovered. To correct this, the vertical stabilizer was extended 10 cm and the pitot tube was moved from the top of the fin leading edge to about midpoint where a sawtooth was also incorporated. The JA model later used the same improvements.

The six tanks in the fuselage and wings held approximately 5,000 litres of fuel with an additional 1,500 litres in an external drop tank. The specific fuel consumption was only 0.63 for cruise speeds (fuel consumption was rated 18 mg/Ns dry and 71 with afterburner). The Viggen's consumption was around 15 kg/s at maximum afterburner, which meant that the internal fuel was exhausted in just seven minutes due to the relative inefficiency of the turbofan over a turbojet at full afterburner. Performance comparisons with other aircraft from the same age are however slightly difficult, since no other fighter or attack aircraft aside from the Harrier and Yak-38 were designed for STOL or VTOL capability.

Armament
A weapons load of up to 7,000 kg could be accommodated on nine hardpoints; one centerline pylon, two fuselage pylons, two inner and two outer wing pylons and two pylons behind the wing landing gear. The centerline pylon was the only wet pylon and was usually occupied by an external fuel tank. The outboard wing pylons were never used in peacetime since aerodynamic flutter loads would structurally fatigue the wing. The pylons behind the landing gear were not used until the JA 37D modification when BOY countermeasure dispensers were fitted to them.

AJ 37
The AJ 37 was designed to carry two RB 04E anti-ship missiles on the inboard wing pylons with an optional third missile on the centerline pylon. An optional load consisted of two RB 05A air-to-surface missiles on the fuselage pylons. The RB 05A was later replaced by RB 75 TV-guided missiles. In a ground-attack role, a combination of unguided 135 mm rockets in sextuple pods and 120 kg fragmentation bombs on quadruple-mounts could be used. Self-defense was provided with either ECM or 30 mm ADEN cannon pods with 150 rounds of ammunition on the inboard wing pylons.

Rockets had warheads of several types: the 50 mm M56GP 4 kg armour-piercing, the M56B with 6.9 kg of HE, and the M70 with a 4.7 kg HEAT warhead. T

For the secondary air-to-air role and self-defence, the Rb 28 IR-missile was initially selected, but was never used due to poor performance. This left the outboard wing pylons unutilised as the Rb 28 was the only missile integrated there up until the AJS modernisation. Instead, RB 24/RB 24J were used on the fuselage pylons and inboard wing pylons or in combination with optional 30 mm underwing ADEN cannon pods.

AJ 37 was under consideration as a carrier of both nuclear and chemical weapons, although no nuclear or chemical weapons were adopted by Sweden.

SH 37
The SH 37 was capable of carrying the same configuration of weapons as the AJ 37. However, since it was only used in the maritime role, only the RB 04E in combination with RB 24/RB 24J for self-defense were employed. The chaff and jammer-pods was the most commonly used load.

SF/SK 37
Both the SF and SK variants lacked the radar and could not carry the guided air-to-surface missiles as the AJ and SH. The SF could carry RB 24/RB 24J for self-defense though. The unguided cannon and rocket pods were also an option.

JA 37
With the introduction of the JA 37 in 1979 came the Ericsson PS 46/A radar capable of guiding the two semi-active radar homing RB 71 missiles on the fuselage pylons simultaneously in combination with RB 24J/RB 24J air-to-air missiles. Unlike the strike variant a KCA 30mm Oerlikon internal cannon was carried as well as 126 rounds, in a conformal pod under the fuselage. The firing rate was selectable at 22 or 11 rounds. The KCA cannon fired 50% heavier shells at higher velocity than the older ADENs, giving a much higher kinetic energy. This, in conjunction with the fire control system, allowed air-to-air engagements at longer range than other fighters. The unguided cannon and rocket pods were available in the secondary ground-attack role.

The centerline pylon was almost exclusively carried a semi-permanent fuel tank, which was jettisonable in the event of a dogfight.

In 1987, the more advanced all-aspect RB 74 air-to-air missile was introduced for the JA 37. With the major upgrade of the JA to JA 37D in 1997 came the ability to carry four RB 99 on the fuselage- and inner wing pylons. In addition, a U95 ECM pod could now be carried under the right wing in place of an AMRAAM as well as chaff and flare dispensers on a pair of hitherto unused pylons just behind the main landing gear on each wing.

AJS/AJSF/AJSH 37
With a need arising to carry the new RB 15F anti ship missile the onboard computer was inadequate. Instead of installing a computer in the missile pylon it was considered more effective to upgrade the onboard electronics.

The extensive electronics upgrade of the old AJ/SF/SH in 1992 gave the ability to carry the Sidewinder on the outer wing pylons which had been unused as well as the ability to carry the newer RB 74. The AJS and AJSH also received the RB 15F anti-ship missile and BK 90 stand-off cluster bomb originally intended for the delayed JAS 39 Gripen.

Operational history
A total of 110 original, ground-attack optimized variant, AJ 37 were built, with the first operational squadron established in 1972 at F 7 Såtenäs.

A two-seat trainer was not initially planned since it was considered that new pilots could get enough experience with delta-winged aircraft on the SK 35 Draken trainer. Eventually, however, 18 SK 37 two-seat trainers were ordered and delivered in 1973. To make room for the second cockpit, one fuel tank and some avionics were removed. The radar was also omitted limiting the weapons load to gun pods and unguided rockets.

A total of 26 of the SH 37 maritime reconnaissance and strike variant were built in 1974, replacing the S 32C Lansen. Although fitted with radar and weaponry, the SH 37 Viggen could also undertake photographic missions with its single long-range camera, while external pods could carry a photographic day-set, a "Red Baron" IR set, an ELINT set, and AQ series ECM (made by SATT).

A further 26 of the SF 37 reconnaissance variant were also delivered to replace the S 35 Draken in 1975. These were recognizable by having an elongated nose, equipped with six cameras and a VKa 702 infrared linescanner for night reconnaissance. Also, the "Red Baron" pod, with three IR cameras was widely used, as well as an ELINT set.

The Viggen saw initial service in natural metal, later receiving an extremely elaborate disruptive camouflage scheme for the AJ/SF/SH/SK variants and the first 27 JA aircraft. The 28th JA was painted in a gray tone that turned out too close to white. All latter JA aircraft were painted in a darker light/dark gray, appropriate for a high altitude fighter.

The final Viggen production variant was the JA 37 interceptor entering service in 1980. The last of 149 JA 37s was delivered in 1990. Differences from the previous models included an improved and more powerful RM 8B engine, a new PS 46/A interception radar, new computers, HUD, ECM and some other subsystems.

Unusually for a 1970s fighter, three multi-purpose CRT display screens were fitted within the cockpit, in a system called AP-12, that also included a new model of HUD. The new radar was compatible with the Skyflash medium-range missiles, for the first time in a Swedish fighter. Two Skyflash missiles could be carried under the wings on hardpoints, as well as four Sidewinder J or L models. Another improvement was the addition of an Oerlikon KCA 30 mm cannon mounted internally, with 126 rounds of 360 g ammunition.

The structural strength was also improved, especially for the multi-sparred wings (initially Viggens had a high loss rate, with 21 aircraft lost in the early years). Various upgrades have been performed over the years, mainly to cockpit equipment, weapons and sensor fit. Between 1998 and 2000, 10 SK 37 trainers were converted to SK 37E electronic warfare trainers to replace the aging J 32E Lansen.

Swedish JA 37 Viggen fighter pilots, using the predictable patterns of Lockheed SR-71 Blackbird routine flights over the Baltic Sea, managed to lock their radar on the SR-71 on numerous occasions. Despite heavy jamming from the SR-71, target illumination was maintained by feeding target location from ground-based radars to the fire-control computer in the Viggen. The most common site for the lock-on to occur was the thin stretch of international airspace between Öland and Gotland that the SR-71 used on the return flight. The Viggen is the only aircraft to this day to get a radar lock on the SR-71.

Retirement
The Viggen has been phased out in favour of the advanced later generation JAS 39 Gripen with the last front line Viggen retired from the Swedish Air Force in November 2005. A few aircraft were kept flying for electronic warfare training against JAS 39 at F 17M in Linköping. The last Viggen flight took place in June 2007.

Survivors
An AJS 37 Viggen (s/n 37098) with the code F 7-52 has been retained and went through a long period of restoration and maintenance to be airworthy again. This Viggen was built in 1977 and served all its active duty in F 15 Wing at Söderhamn. It was transferred into civil registry with the registration number SE-DXN. It undertook its maiden flight after been approved by the authorities on 27 March 2012 from the F 7 Wing at Såtenäs. The Viggen will be unpainted to represent the first delivered Viggens as they looked in the early 1970s.

Variants
in chronological order
 * AJ 37: Primarily a single-seat ground-attack fighter aircraft, with a secondary fighter role. First delivery in 1971, serial numbers 37001-37108. RM 8A powerplant. PS 37A radar. Partially decommissioned in 1998, 48 airframes upgraded to AJS 37.


 * SK 37: Two-seat trainer aircraft, first delivery in 1973, serial numbers 37801-37817. No radar. Decommissioned in 2003, 10 airframes converted to SK 37E.


 * SF 37: Single-seat photographic reconnaissance aircraft, first delivery in 1975, radar replaced with four cameras, serial numbers 37950-37977. Partially decommissioned in 1998, 13 airframes upgraded to AJSF 37.


 * SH 37: Single-seat maritime reconnaissance and strike aircraft, first delivery in 1975, PS-371A radar, serial numbers 37901-37927. Partially decommissioned in 1998, 25 airframes upgraded to AJSH 37.


 * Saab 37E Eurofighter: Proposed NATO replacement of F-104 Starfighter in 1975, none built.


 * Saab 37X: Proposed export version, none built.


 * JA 37: Primarily a single-seat all-weather interceptor fighter, with a secondary attack role. First delivery in 1979, serial numbers 37301-37449. A 10 cm stretch in the shape of a wedge wider at the bottom than on the top of AJ 37 fuselage between canard and main wing. PS 46A LD/SD radar. Partially decommissioned in 1998, some upgraded to JA 37D.


 * AJS/AJSF/AJSH 37: Upgrade of some AJ/SF/SH 37 between 1993 and 1998. Avionics and software upgrade. 48 AJ 37 airframes modified. 25 SH 37 airframes modified. 13 SF 37 airframes modified. Decommissioned in 2005.


 * JA 37C: Upgrade of older JA 37, avionics and software upgrade.


 * JA 37D: Upgrade of older JA 37 between 1993 and 1998, avionics and software upgrade. 35 airframes modified.


 * JA 37DI: Upgrade of JA 37D, avionics and software upgrade. 20 airframes modified.


 * SK 37E: Electronic warfare trainer, conversion of 10 obsolete SK 37 trainers from 1998 to 2000, serial numbers 37807-37811 & 37813-37817, decommissioned in 2007.

Operators

 * Swedish Air Force
 * Swedish Air Force

Operational units

 * F 4 Frösön
 * 2 squadrons JA 37 1983-2003
 * 1 squadron SK 37 1999-2003
 * 1 squadron SK 37E 1999-2003
 * F 6 Karlsborg
 * 2 squadrons AJ 37 1978-1993
 * F 7 Såtenäs
 * 3 squadrons AJ 37 1972-1998
 * 1 squadron SK 37 1972-1974
 * F 10 Ängelholm
 * 1 squadron AJ/SF/SH 37 (combined) 1993-2001
 * F 13 Norrköping
 * 1 squadron SF/SH 37 (combined) 1977-1993
 * 1 squadron JA 37 1980-1993
 * F 15 Söderhamn
 * 2 squadrons AJ 37 1974-1998
 * 1 squadron SK 37 1974-1998
 * F 16 Uppsala
 * 2 squadrons JA 37 1986-2003
 * F 17 Kallinge
 * 1 squadron JA 37 1981-2002
 * 1 squadron SF/SH 37 (combined) 1979-1993
 * 1 squadron JA 37 1993-2002
 * F 21 Luleå
 * 2 squadrons JA 37 1983-2004
 * 1 squadron SF/SH 37 1979-2002
 * 1 squadron SK 37E (combined) 2003-2007

Lack of commercial success
Although the Viggen was offered for sale worldwide, and regarded as a very competent aircraft, no export sales occurred. Reasons to explain Saab's failure to sell a competitively priced, highly advanced and well-respected aircraft include the Swedish government's relatively strict controls on arms exports to undemocratic countries, potential customers' doubts about continuity of support and supply of spare parts in the event of a conflict disapproved of by Sweden, and strong diplomatic pressure of larger nations. The United States blocked an export of Viggens to India in 1978 by not issuing an export license for the RM8/JT8D engine, forcing India to choose the SEPECAT Jaguar instead. Indian interest in the Viggen was reported to be entirely by Rajiv Gandhi's influence, with no input from the Indian Air Force.