The JA37DI is a variant of the Swedish JA37D fighter jet developed to meet NATO standards. Following the end of the Cold War, Sweden began moving away from neutrality, actively expanding its cooperation with NATO by participating in Alliance operations and exercises. However, earlier aircraft were only compatible with Swedish systems, so they needed to be upgraded to international standards. In the early 2000s, 21 JA37D aircraft were upgraded to the JA37DI standard; the "I" stands for "interoperability". The most significant change to the aircraft was the installation of the FR31 radio. Like the other Viggen fighters, the JA37DI was retired from service in 2004.

The history of the F21 Luleå squadron began in 1941 when the Swedish Air Force established a new squadron to defend the Norrbotten region under pressure from politicians. However, the squadron did not receive any military aircraft and had to make do with Beechcraft Model 18 transport planes until 1949. That year, the transport aircraft were replaced by reconnaissance "Mustangs", Saab 18s, and others. By 1953, the squadron had transitioned to S28 Vampire jet fighters. In 1963, it became a fighter-reconnaissance unit when it received the J32B. The JA37s arrived in 1983 and the 37Ds in early 2002. By June 2004, the JAS39 had replaced them, bringing the history of the "Viggen" in the squadron to a close. The F21 still exists today and flies the JAS39C/D.

The JA37DI F21 was introduced in Update 2.41 "Firebirds". The DI differs from its predecessor, the JA37D, in that it is equipped with RB 99 air-to-air missiles, also known as AIM-120s. However, these new, effective missiles do not address the fighter's key issues. It is no longer fast or agile enough, and its RWR and radar are outdated. This makes the aircraft difficult to use effectively in combat. The only difference between the standard JA37DI and the JA37DI F21 is its unique camouflage.