At the time it entered service, the Swedish Stridsvagn Strv 103 (popularly known as the "S-tank") caused great interest as it appeared to provide a new way forward for tank design, leading to lighter and more mobile three-man MBTs. Its design originated in the 1950s, with the Swedish firm of Bofors being awarded the development contract in 1958. The first two prototypes were completed in 1961 followed by 300 production tanks produced between 1966 and 1971.
The S-tank's crew are all located in a central fighting compartment. The driver/gunner is on the left, facing forwards; behind him sits the radio operator, who faces to the rear and who drives the tank backwards, when required. The commander sits on the right of the gun and also has an accelerator and brake to control the vehicle, if required.
Main armament is the L74 105mm. rifled gun, a lengthened version of the British L7 gun, produced in Sweden. The barrel is mounted rigidly in the glacis plate thus doing away with the need for a turret. This results in reduced overall height for the tank and reduced weight , since there is no turret or recoil mechanism, and also enables an automatic loader to be installed. This device holds 50 rounds, a mix, as required by the tactical situation, of APDS, HESH, HE and smoke. The tank can fire 10-15 rounds per minute and empty cases are automatically ejected through a hatch in the rear of the hull.
The power pack in the S-103A and S-103B versions was a Rolls-Royce K60 diesel, which was used for normal operations, and a Boeing gas-turbine which was brought in to provide additional power for combat or when crossing difficult terrain. In the Strv-103C, however, the Rolls-Royce engine was replaced by a more powerful Detroit Diesel 6V-53T, although the gas-turbine was retained unchanged. Additional fuel tanks and a new laser rangefinder were also added to this version. The last version was the S-103D, basically an upgrade from the C model with the installation of a fire-control computer, thermal viewers for both the gunner and the commander, allowing the crew to fight at night-time and in bad weather conditions, and the installation of passive light enhancers for driving. Other minor changes to the suspension system and engine were also made. This version did not go further the prototype stage.
The hydropneumatic suspension was used to aim the gun. The gun is laid in elevation by the driver/gunner, who adjusts the suspension to alter the elevation between +12º and -10º. The gun is traversed by slewing the tank in its tracks. When the gun is fired the suspension is locked to provide a stable platform.
The S-tank bristles with innovations, which caused much excitement when it first appeared. It was widely tested, the British army even leasing sufficient to equip a complete armoured squadron in Germany for a protracted field trial. However it has proved less successful than first thought. It must expose a large cross-sectional area when in a hull-down firing position and cannot fire with any accuracy on the move. No further designs of this type have been produced.
The S-tank was replaced by the Leopard 2(S) from 1997 onwards, the German tank having won against competition from the French Lecrec and the US M1 Abrams.