The Stridsvagn 103 (Strv 103), also known as the Alternative S and S-tank, is a Swedish Cold War–era main battle tank, designed and manufactured in Sweden. "Strv" is the Swedish military abbreviation of stridsvagn, Swedish for tank (literally combat wagon, it also is the Swedish word for chariot), while the 103 comes from being the third tank in Swedish service to be equipped with a 10.5 cm gun.
Developed in the 1950s, it was the first main battle tank to use a gas turbine engine and the only mass-produced tank since World War II to not use a turret besides the German Kanonenjagdpanzer, which is not classified as a tank by role, but by design. It has an unconventional design with a unique gun laying process: it is turretless with a fixed gun traversed by engaging the tracks and elevated by adjusting the hull suspension. 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 the 1990s, when, along with the Centurions, it was replaced by the Leopard 2 variants Stridsvagn 121 and Stridsvagn 122.Strv 121 & strv122
While most turretless armoured fighting vehicles are classified as assault guns or tank destroyers, the Strv 103 is considered a tank since its designated combat role matched those of other tanks within contemporary Swedish doctrine.
History Concept development In the early 1950s, the Royal Swedish Army Materiel Administration's Ordnance Department began development of a new tank known as kranvagn, or KRV. The desired features were a weight around 30 tonnes with high gun performance, protection and mobility. The new design emerged with a very low-profile hull with a tall and highly angled turret mounting a large-calibre main gun and autoloader system, reducing the crew to three. 105 to 120 mm guns were initially considered, with the 120 being favoured, and later a 155 mm design was also considered. The overall design is very similar to the French AMX-50.
Around this same time, they also approached the United Kingdom about purchasing the Centurion tank. The Centurion included a gun stabilizer, much better mobility, and a number of other features that made it much more advanced than the KRV. Although the British proved interested, they stated that deliveries could not begin until the 1955 or 56 time-frame, after their own needs were filled. Then, in 1953, due in part to a need for increased foreign currency, the UK offered to deliver the Centurion immediately. This offer was taken up, and KRV work continued only to produce two hulls for study.
While the Centurion was a great advance on the KRV, it was still considered much heavier than ideal given its firepower. In the mid-1950s, the Royal Swedish Army Materiel Administration's Ordnance Department put out a contract to find a replacement. Two working groups were formed to consider different approaches. "Alternative A" (for "Anglo-American") was to purchase a design from either the British or Americans of roughly 50 tons but mounting a more powerful gun than the Ordnance QF 20-pounder of the existing Centurions. "Alternative T" ("Tysk-Fransk", or "German-French") was for a lighter tank of around 30 tons with less protection but better mobility. In 1956, Sven Berge of the Swedish Arms Administration proposed "Alternative S" ("S" standing for "Swedish"), a radically different solution.
Alternative S As part of the Centurion purchase, the UK had supplied volumes of data from World War II and Korean War tank engagements. These demonstrated that a full half of all "kills" were due to hits on the turret or the turret ring. Hits on the lower portion of the tank were much more rare. These statistics also suggested that the chance of being hit was strongly related to the overall height of the tank.
In 1943, Berge had read reports of the 1940 French Char B1 design. This featured a large (for the era) gun in the hull that was fixed in azimuth, and required the entire tank to turn to aim it. This was accomplished through the use of a complex transmission system under the gunner's control. Berge had also been part of the teams that examined German vehicles after the war, and was aware of the ability for short vehicles to quickly maneuver.
Berge combined these concepts for the S proposal. The suspension would be connected to a stabilizer from Bofors that would keep the entire tank stabilized as opposed to just the gun. He felt the stabilizers of the era did not offer the performance needed for real fire-on-the-move; while a first shot may be made on the move, the tanks generally stopped for follow-up shots. He felt that the advantage offered was limited, and that better protection when stopped would be more useful.
The resulting chassis was quite small, with only four road wheels, and the gun extended through the vehicle to the rear where the autoloader and ammunition was stored outside of the crew compartment. The resulting 30 ton design offered the same level of armour as the heavy tanks, but was better protected overall due to the external ammunition and very low profile.
Prototypes
A spring 1957 meeting to consider the various designs resulted in "S" raising enough interest that a demonstration of its design features was needed. A small contract was let to demonstrate that the suspension system could be used for aiming. This led to experiments using a surplus M4 Sherman and Infanterikanonvagn 103 vehicles fit with external systems that moved the suspension. These seemed promising, so one of the test hulls from the earlier KRV program was adapted for more rigorous testing and the first application of the stabilizer. This was later modified to remove the first and sixth road wheels to make a layout with greater similarity to the S proposal.
As part of the Försvarsbeslut 1958 (defence plan of 1958) deliberations, the Riksdagen (Swedish parliament) debated the three Alternatives. S would be the most expensive, but it was ultimately selected for the symbolic value of a domestic tank in a neutral country, as well as the spin-off effects on Swedish industrial competence. On 4 February 1958, a contract was released for two prototype hulls, S1 and S2. Volvo was selected to build the engine system and AB Landsverk the drive trains. S1 used an electric motor for power, supplied by a generator trailer, and was used to test the suspension system. S2 included the Volvo-designed Diesel-turbine hybrid engine and was used to test the drivetrain and flotation system. These were also successful, and in 1960, an order was placed for ten pre-production vehicles.
By this time, the UK had offered the latest Centurion Mk. 10, which featured the famed Royal Ordnance L7 105 mm gun. The gun had been licensed for production in Sweden and would be available shortly, so the decision was made to replace the much larger guns originally conceived with the 105 in order to save development costs. For the S, it was lengthened to L/62 from the original L/52 to allow more powerful charges to be used. Because the gun was fixed in place, with no recoil movement, the autoloader was able to reach a very high rate of firing every three seconds. This led to the production design being given the name "Stridsvagn 103", meaning the third design mounting a 10 cm gun.
The first of these "zero series" vehicles arrived in 1963. During testing, it was noticed that while a two-man crew could operate the vehicle successfully, other tasks became more difficult. Notably, it made operating in the field more difficult because a two-man crew was not enough to perform guard duty or easily perform track maintenance or reloading ammunition. The decision was made to add a third member, assigning them to operate the radios as well as having a second set of controls and vision systems to allow them to drive the tank in reverse at high speed.
The vehicle was first shown to the public in the spring of 1963. It was an immediate worldwide sensation. John F Kennedy expressed an interest in the design, leading to a memo by Robert S McNamara noting:
Into production The zero-series success led to a fall 1964 production order for 70 examples. The first production examples began to arrive in 1967. These demonstrated that the original Boeing T50 turbine was underpowered, and a new design from Caterpillar was introduced for the second production batch, the 220 S103B models, which began to arrive in 1970. These engines were retrofit to the earlier examples as well. The production of 290 production models was complete by 1971.
Later updates Plans during the 1970s called for new tanks to be introduced in the 1980s, but these were later pushed back to the 1990s. This led to a round of improvements for the S103's in service, producing the S103C. The changes were to replace the Rolls-Royce K60 with the Detroit Diesel Series 92, new tracks from Diehl Aerospace, external fuel tanks along the sides of the vehicle, a laser rangefinder, and the addition of the dozer blades to all of the tanks, instead of every third vehicle. Conversions began in 1986 and were complete by 1988.
There was some development of a S103D model carried out in the 1990s. Yet another turbine was used, along with a nuclear biological chemical filter system, a new ballistic calculator able to fire on moving targets, a muzzle reference system, better damping of the suspension, improved frontal armor and a separate stabilizer for the commander's machine gun. By this time the newer foreign tanks were selected for purchase and the D-series modifications were not carried out.
Design
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 did not give the Strv 103 any significant advantage over its most likely opponent, the T-62. The latter was just slightly taller with in height with its turret versus the of the Strv 103. On the other hand, the Swedish Centurions towered over both with their – in height. However, the T-62 paid for its low profile with an extremely cramped interior and lack of gun depression. Tanks are often deployed in 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 and 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 by adjusting the suspension.