Swedish tank designers spent a lot of time working on a heavy tank known as the KRV. The result was an unusual vehicle that would have had a 155 mm gun with an automatic loading mechanism in the turret, similar to the French AMX 50. The design was too heavy and too expensive, and only experimental chassis with no armament were built. It turned out to be cheaper to buy Centurion Mk.3 tanks from the British, adopted as Strv 81. However, the Centurions did not entirely satisfy the military. These tanks were about as large and heavy as the KRV, and even later Strv 101 (Centurion Mk.10) tanks with an improved 105 mm L7 gun did not entirely satisfy firepower requirements.
Sven Berge headed a project for a new tank. The first blueprints are dated 1956, and by 1957, three new potential designs were ready:
- Strv A: 42.5 tons, well armoured, with a loading mechanism, comparable in size with the American M60, and rather slow.
- Strv T: 32.5 tons, similar to the Leopard 1 in design. Effective power was about 25-30 hp/ton, armour was no greater than 75 mm.
- Strv S: a completely new concept of a turretless tank. Its combat mass was estimated at 30 tons and it had extremely good protection due to its low silhouette.