The AJS37 Viggen is an updated version of the Swedish AJ37 ground-attack aircraft. "AJS" stands for "attack-jakt-spaning", which translates to "attack-fighter-reconnaissance", and "Viggen" means "lightning" in Swedish. In the early 1990s, the Swedish Air Force decided to extend the service life of the AJ, SH, and SF 37 aircraft by modernizing them to enable the AJ aircraft to conduct reconnaissance missions. Between 1993 and 1998, 48 aircraft received upgrades, including two additional pylons for air-to-ground missiles, expanded anti-ship armament to include the RB 15F missile, and the ability to carry four RB 75 missiles instead of two, as well as BK 90 guided cluster bombs. The upgraded Viggen aircraft remained in service until 2005 and did not participate in any armed conflicts.

The AJS37 (Early) was introduced in Update 2.57 "Heavy Cavalry". This aircraft stands out for its high maximum speed, thrust reversers, and ability to carry four RB 74 missiles, a Swedish-licensed copy of the American AIM-9L all-aspect missile. However, the aircraft lacks a built-in cannon, has weak ground-attack armament, and quickly loses energy during maneuvers. It is identical to the later AJS37.