The Strv 121 is the Swedish designation for the Leopard 2A4, leased from Germany in early 1994 to replace the aging Strv 103 and the Strv 104. A total of 160 Strv 121s were acquired from the leasing deal and all of the vehicles would be delivered to Sweden at the end of 1994 and early 1995. In Sweden, the Strv 121 would go through some changes like being equipped with Swedish radio equipment, reflective tape, and new lights for road traffic, but were also painted in Swedish army camouflage. The Strv 121 would serve until the early 2000s when they were initially phased out for the Strv 122.

The Strv 121 was introduced in Update 1.97 "Viking Fury". With a similar playstyle as the other Leopard 2A4s, it is able to compete with the other nations' top MBTs like the T-80, M1A2 Abrams, and Leclerc. The Strv 121 is agile and can manoeuvre around the battlefield with its high top speed, allowing it to reach capture points and good positions fast. The Strv 121 has a relatively vulnerable hull compared to the more well-armoured turret, and will excel in a hull-down position like most MBTs. Its 120 mm cannon gives it excellent firepower to deal with most opponents and has great penetration capability at further ranges, making it an excellent vehicle to have long distance engagements with enemies where the armour will have an improved chance of protecting the vehicle.