Stridsvagn 103

The Stridsvagn 103 (Strv 103), or S-Tank, was a Swedish tank (although some consider it to be a tank destroyer). It was known for its unconventional turret-less design, with a fixed gun traversed by engaging the tracks and elevated by adjusting the hull suspension. The S-Tank 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 defense and heightened crew protection level. S-Tanks formed a major portion of the Swedish armored forces during the 1960s, 70s, 80s and part of the 90s, but have since been removed from service in favour of the Leopard 2.

History
In the mid-1950s the Swedish army put out a contract tender for a new tank design to replace their Centurions. Although the Centurion was arguably the best tank in the world at the time, its performance lead over contemporary Soviet designs like the T-55 was only marginal, and any future designs would best it. A consortium of Landsverk, Volvo and Bofors responded with a new heavy tank design, known under the codename KRV, fitted with a 155mm smoothbore gun in an oscillating turret. But this would be an expensive option and the Army started looking at British, German and American tanks.

Sven Berge of the Swedish Arms Administration then in 1956 proposed Alternativ S, a domestic alternative (S stands for Swedish). Noting that the chance of being hit in combat was strongly related to height, he proposed that any new design should be as low as possible. The only practical way to do this was to eliminate the turret (which would also make the tank much lighter and simpler), though in terms of absolute height, this still did not give the Strv 103 any significant advantage. Its most likely opponent after all, the T-72, is only 2.23 meters in height with its turret versus the 2.14 meters of the Strv 103 (a mere 3.5 inches shorter). However, tanks occasionally deploy themselves into hull-down firing positions, either purpose dug or using the crest of a hill, in order to reduce the exposure of the vehicle to enemy fire. In this firing position the level of exposure is determined by the distance between the bottom of the gun barrel to the top of the turret or vehicle, and the angle to which the vehicle is able to depress the gun barrel. Because the Strv 103 orients the entire tank to depress and elevate the barrel, in a hull down position it has a very low apparent height and subsequent visual profile to the enemy. It can also lower the hull 13 centimeters. Such static use of a tank is at odds with the very concept of a tank, i.e., a mobile, protected gun platform able to bring heavy firepower to bear upon the enemy while attacking. Hence the S-Tank must be considered a strictly defensive vehicle.

This is not the first time such a system had been used: it was common among World War II-era tank destroyers and assault guns, but in a tank, the ability to quickly aim a turret provided always proved to be great asset. However, some tank destroyers, such as the Jagdpanther, were both relatively cheap to make and very effective in defensive positions. Berge's design tried to solve the aiming problem through the use of a fully automated transmission and suspension system, which would turn and tilt the tank under gunner control. The gun itself would be fixed to the hull. Unfortunately, this made it impossible to use a stabilized gun. As a result, the tank could not accurately move and fire at the same time. However, during the period the S-tank was in service, turreted tanks rarely fired on the move, and especially not when used defensively.

Other features of the tank were also quite radical. The gun, a Bofors 105mm L/62 (and able to use the same ammunition as the British 105mm L7) would be equipped with an autoloader, allowing the crew to be reduced to two; most designs of the era used a crew of four, while the S-Tank would eliminate the loader and gunner. Room was available for an extra crew member, the rear driver, who faced the rear of the tank equipped with a complete setup for driving. This allowed the tank to be driven backwards at the same speed as forwards, keeping its frontal armour pointed at the enemy.

The commander and gunner/driver both had the same set of sights and controls to fire the gun and drive the tank. Additionally the tank was powered by two engines, a 240 hp Rolls-Royce K60 diesel for cruising and turning the tank for aim, and a 300 hp Boeing 502 turbine for dashing at high speed. This was the first use of a turbine engine in a production tank; the Soviet T-80 and US M1 Abrams would later be built with gas turbines for main propulsion.

The concept was interesting enough that Bofors was asked to build a prototype of the suspension/drive train, which they completed successfully. In 1958 a follow-on contract called for two production prototypes, which were completed in 1961. By this point, the army was so satisfied with the design that an initial pre-production order of 10 was placed in 1960. With minor changes, the S-Tank was adopted as the Stridsvagn 103 (103 from the fact that it was the third tank accepted with a 10 cm gun) and full production started in 1967 and ended in 1971 with 290 delivered. The changes included a new gyrostabilised commander's cupola armed with a 7.62 mm KSP 58, and upgraded frontal armour. A screen, similar to those of the Panzer IV Ausf. J of World War Two, was available to help defeat HEAT rounds; however, it was kept secret for many years and was only to be fitted in the event of war.

The Strv 103 was fully amphibious. A flotation screen could be erected around the upper hull in about 20 minutes, and the tracks would drive the tank at about 6 km/h in water. One tank in each platoon was fitted with a blade under the front hull that allowed it to dig itself into the ground for added protection.

The Stridsvagn 103 never saw combat and so its design remains unproven, unlike turreted main battle tanks. However, for its intended role in the 1960s it had numerous advantages. In 1967, Norway carried out a two week comparative observation test with the Leopard 1 and found that with closed hatches the 103 spotted more targets and fired faster than the Leopard. In April to September 1968, two 103s were tested at the British armour school in Bovington, which reported that "the turretless concept of the "S"-tank holds considerable advantage over turreted tanks". In BAOR 1973, the 103 was tested against the Chieftain. Availability never fell under 90% and the final report stated, "It has not been possible to prove any disadvantage in the "S" inability to fire on the move." In 1975, two 103s were tested at the American armour center at Fort Knox. The trial demonstrated the 103 fired more accurately than the M60A1E3, but on an average 0.5 seconds slower.

Strv 103B
As the weight of the Strv 103 had increased compared to the pre-production tanks the 103 turned out to be underpowered. Hence a more powerful version of the same gas turbine, manufactured by Caterpillar, was introduced after the first production run of 80 tanks. The early version was soon upgraded to B-standard.



Strv 103C
An upgrade program was started in 1986 to fit all vehicles with improved fire control systems. Also, each S-Tank was fitted with a dozer blade, rather than just one per platoon. A further upgrade in 1987/88 replaced the Rolls-Royce engine with a newer 290 hp (216 kW) Detroit Diesel with additional fuel tanks, and added a new laser rangefinder. There was some consideration of adding both reactive and/or appliqué armour in the early 1990s, but in the end the S-Tank was instead phased out of Swedish service in favour of the Leopard 2, which entered service in 1997. The last year in which the S-Tank were used to train tank crews was 1997.

Strv 103D
In the mid-1990s, as the Swedish armed forces were looking for a new main battle tank, one Strv 103C was upgraded into the Strv 103D. The major changes were the installation of 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. Some minor changes to the suspension system and engine were also made.

This prototype was used during the trials for the new main battle tank system for the Swedish armed forces alongside all the other tanks tested. For a few years this prototype was even tested under remote control. The only Strv 103D ever built is today on display at the Axvall armor museum, together with some 103C models. They are all still in running order.