Since 1994, Sweden has been armed with an export version of the Leopard 2A4, locally called Stridsvagn 121 or abbreviated Strv 121. After 2000, the idea arose to upgrade the Strv 121 to the level of the Strv 122 through modernization. One of the tanks was converted as a prototype, receiving the designation Strv 121B and its own name Christian II (in honor of Christian II, King of Denmark, Norway and Sweden). It had updated electronic equipment and more modern smoke grenade launchers installed.

The Strv 121B is armed with a 120 mm smoothbore cannon with a 7.62 mm coaxial machine gun, and is also equipped with a 7.62 mm AA machine gun. The ammunition includes APFSDS and HE shells. Additionally, the tank is equipped with a laser rangefinder, a thermal vision device for the gunner, a night vision device for the commander and driver, and is also equipped with smoke grenade launchers.