The Stridsvagn 103 (Strv 103), also known as the S-Tank, was a Swedish post-war main battle tank. It was known for its unconventional turretless design, with a fixed gun traversed by engaging the tracks and elevated by adjusting the hull suspension. Turretless armoured fighting vehicles are more commonly classified as tank destroyers, but serve a different purpose. The Strv 103 was designed and manufactured in Sweden.
The Strv 103 was developed in the 1950s and was the first main battle tank to use a turbine engine. The result was a very low-profile design with an emphasis on defence and heightened crew protection level. Strv 103s formed a major portion of the Swedish armoured forces from the 1960s to part of the 1990s, but have since been removed from service in favour of the Stridsvagn 122.