Stridsvagn 103

The Stridsvagn 103 (strv 103), ^{[Note 1]} also known as the S-Tank,^{[Note 2]} was a Swedish post-war main battle tank.^[5] It was known for its unconventional design: it was turretless with a fixed gun traversed by engaging the tracks and elevated by adjusting the hull suspension. While turretless armoured fighting vehicles are usually classified as assault guns or tank destroyers, despite its unique gun laying process^[6][7][8] the Strv 103 is considered a tank because its designated combat role matched those of other tanks within contemporary Swedish doctrine. It is the only tank of any kind since World War II to dispense with a turret.

The Strv 103 was designed and manufactured in Sweden. It 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 survivability and heightened crew protection level. Strv 103s formed a major portion of the Swedish armoured forces from the 1960s to part of the 1990s, when, along with the Centurions, it was replaced with the Stridsvagn 121 and the Stridsvagn 122.

History

In the mid-1950s, the Kungliga Arméförvaltningens Tygavdelning put out a contract tender for next generation tank design to replace their Centurions. A consortium of Landsverk, Volvo and Bofors responded with a suggestion to revive an earlier domestic heavy tank design, known under the codename KRV, fitted with a 155 mm smoothbore gun in an oscillating turret. However, this was deemed too expensive in comparison to the alternatives: A(ngloamerican), which was to purchase a 50-ton tank with high protection and mediocre mobility from either U.K. or U.S.A. Alternative T(ysk-fransk /German-French) was a 30-ton tank with low protection and good mobility. Then, in 1956, Sven Berge of the Swedish Arms Administration proposed Alternativ S, a domestic alternative (S standing for Swedish).

Development

Studies of casualty reports from World War II and the Korean War revealed that the risk of being hit in combat was strongly related to height, with more than half of tank losses being the result of the turret being penetrated. Berge therefore concluded that any new design should be as low as possible. The radical solution was to eliminate the turret, which would also dispose of a vulnerable target area and make the tank much lighter. In terms of absolute height, the final design (see below) did not give the Strv 103 any significant advantage. Its most likely opponent, the T-64, was only 2.20 m (7 ft 3 in) in height with its turret versus the 2.14 m (7 ft 0 in) of the Strv 103. However, the T-64 paid for its low profile with an extremely cramped interior and lack of gun depression. Tanks often deploy themselves into hull-down firing positions, either behind dug entrenchments 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. Since the Strv 103 orients the entire tank to depress and elevate the barrel, in a hull down position it has very little apparent height and subsequent visual profile to the enemy. It could also lower the hull a further 13 cm by adjusting the suspension.

Berge's design solved the aiming problem through the use of a fully automated transmission and suspension system, which precisely turned and tilted the tank under the gunner's control. The gun itself would be fixed to the hull. This made it impossible to use a stabilized gun. As a result, the tank could not accurately move and fire at the same time, but the Swedish experience with Centurions suggested that, in order for tanks to reach acceptable accuracy, they would need to come to a halt anyway, and that no breakthrough in stabilisation technology was likely within the foreseeable future.

Other features of the tank were also quite radical. The rifled gun, a Bofors 105 mm L74 with a barrel length of 62 calibres, was able to use the same ammunition as the British Royal Ordnance L7, and would be equipped with an autoloader allowing a rate of fire of one round every third second, also allowing the crew to be reduced to two; a gunner/driver and the commander (most designs of the era used a crew of four), with a single person being able to handle all functions of the tank from his ordinary position due to duplicate controls. This would of course only be used in emergencies, as the workload would be overwhelming, but apart from providing redundancy it also allowed the crew to shift tasks between them as situation required. The concept went through practical tests, that quickly revealed that a two-man crew would not be self-sufficient when considering the many tasks not directly related to handling the tank: in particular, routine maintenance, bivouacking, track-changes and reloading in field. While the last issue could have been solved by adding staff to the ammunition crews, it was decided that a third crew-member was needed. To enhance combat effectiveness, the third man was to be assigned as rear driver/radio operator, facing the rear of the tank and 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, while relieving the commander of routine radio duty. The commander and gunner/driver both had the same set of sights and controls to fire the gun and drive the tank.

Gun depressed using suspension.

Gun elevated using suspension.

The tank was powered by two engines, a 240 hp Rolls-Royce K60 opposed-piston diesel for slow cruising and manoeuvring the tank in aiming, and a 300 hp Boeing 502 turbine for additional power when travelling at higher speed or in severe terrain. The turbine was quickly found to be underpowered, and was replaced by a Caterpillar turbine delivering 490 hp after no more than 70 tanks had been produced, and retrofitted to all previous vehicles. 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.

Service

In preparation for the defence decision of 1958 (Försvarsbeslut 1958 (FB58)) in the Swedish parliament (Riksdagen), the procurement set Alternativ S against the two foreign alternatives Alternativ A and Alternativ T. While the domestic alternative was going to be more expensive, the defence committee report recommended "S" when weighing in the symbolic value of a domestic tank for a neutral country as well as the spin-off effects on Swedish industrial competence.

Riksdagen made the formal decision regarding FB58 on 4 February 1958, and 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 for 10 was placed in 1960.

With minor changes, the Alternativ S was adopted as the Stridsvagn 103 ("103" from being the third tank with a 10 cm calibre gun accepted into Swedish service). Full production started in 1967 and ended in 1971 with 290 delivered. The changes included a new gyro-stabilised commander's cupola armed with a 7.62mm KSP 58 machine gun, and upgraded frontal armour. A unique grid could be mounted at the front 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 kilometres per hour (3.7 mph) 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.

Performance

The Stridsvagn 103 never saw combat and so its design remains unproven. 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 while the situation was reversed when operating with hatches open. 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 1973, the BAOR tested the 103. British crewmen received 6 weeks training and the vehicles were serviced by Swedish engineers. Over nine days of manoeuvres alongside the Chieftain tank, 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."^[9] In 1975, two 103s were tested at the American armour center at Fort Knox. The trial demonstrated that the 103 fired more accurately than the M60A1E3, but on an average 0.5 seconds more slowly.^[10]

Versions

Stridsvagn 103B

Strv 103C at the Swedish Army Museum, Stockholm, with anti-HEAT slat armor on the front.

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 tanks (retroactively designated Strv 103A) were soon upgraded to B-standard. Adjustments to the hydro-pneumatic suspension increased elevation range from -10 through +12 degrees, to -11 through +16 degrees.^[11]

Stridsvagn 103C

An upgrade programme was started in 1986 to fit all vehicles with improved fire control systems. Also, each Strv 103 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 cans placed on along the sides to functions as applique armour, and added a new laser rangefinder.

Stridsvagn 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.

There was some consideration of adding both reactive and/or appliqué armour in the early 1990s, but, in the end, the Strv 103 was instead phased out of Swedish service in favour of the Stridsvagn 122 (Strv 122), which entered service in 1997 (the last year that the Strv 103 was used to train tank crews).

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 sole Strv 103D is today on display at the Axvall armor museum,^[12] together with some 103C models. They are all still in running order.

See also

• List of tanks
• FV4401 Contentious
• VT tank

Notes

References

Sources

• "Stridsvagn 103 S (E1995.105)". Bovington Tank Museum vehicle collection. tankmuseum.org. Retrieved 23 October 2010. 
• Stridsvagn 103 S (E1995.105) at The Tank Museum
• Historien bakom Stridsvagn 103 "S" (Swedish)

External links

Wikimedia Commons has media related to Stridsvagn 103.

• Society S-tank- Welcome to The S tank association - official site of the S tank association
• "Vapenverkan mot Stridsvagn 103" 20:28 minutes, English subtitles