The Swedish-originated Stridsvagn 103 (Strv 103) - also known as the "S-Tank") was one of the more extreme departures from conventional main battle tank design during the Cold War years. Still classified as a Main Battle Tank (MBT), the Strv 103 did away with a traditional turret mounting the main gun armament, instead opting for a lower profile design which could be embedded into earthen ditches and utilized in a defensive manner against incoming enemy armor. As such, the Strv 103 tank was developed along the lines of defensive positioning doctrine, its main gun set directly into the hull.
This compact approach allowed for an operating crew of just three personnel, the first two crew in the forward hull and the remaining crewmember positioned in the rear hull, facing rear, complete with a full driving console allowing the vehicle to be piloted in a rearwards motion should the vehicle be required to flee, the main armament still pointed at the enemy. The crew included a driver (doubling as the gunner), the vehicle commander and a radio-operator (doubling as the rear-facing driver). The hull was armored up to 100mm and could be made amphibious with approximately 25 minutes required for preparation.
All Strv 103s were fitted with a dozer blade for which to dig out earth. The low profile nature of the vehicle allowed for a harder target to enemy guns. The obvious drawback to the design lay in its fixed main gun which required the entire vehicle to be turned to face the enemy. The tank was designed to replace British Centurions which stocked the Swedish Army inventory at the time. Main armament of the Swedish successor was the 105mm Bofors L/62 rifled gun. This was coupled to two fixed 7.62mm KSP 58 machine guns with an optional KSP 58 MG serving as an Anti-Aircraft (AA) measure. The main gun was mated to an auto-loading feature which allowed the crew number to be kept to a minimum.
Production of Strv 103s spanned from 1967 to 1971 with 290 units completed. The Strv 103 never saw combat service. All S-Tanks were eventually removed and retired from service by 1997 as the Swedes adopted the excellent German Leopard 2 MBT in its place.
Three major marks of the Strv 103 ultimately emerged. The Strv 103A was outfitted with either a Rolls-Royce K60 diesel engine of 240 horsepower or a Boeing GT502 gas turbine of 300 horsepower. The Strv 103B followed with either a Rolls-Royce K60 diesel of 240 horsepower or a Caterpillar 553 series gas turbine of 490 horsepower. The Strv 103C was offered a Detroit Diesel 6V53T of 290 horsepower or Caterpillar 553 gas turbine of 490 horsepower. All rode on a gas-hydraulic hydropneumatic suspension system. The powerpacks included a 2 -forward, 2-reverse speed transmission system. Road speeds reached 31 miles per hour with a 240 mile road range. Dimensions included a length of 29 feet, 6 inches, a width of 12 feet and a height of 7 feet.
A D-model was proposed as a new 1990s decade MBT replacement, completed in a single example from a modified Strv 103C, and never adopted.