Editing Stridsvagn 103 (section)

== 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 [[Emil (tank)|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&nbsp;mm guns were initially considered, with the 120 being favoured, and later a 155&nbsp;mm design was also considered. The overall design is very similar to the French [[AMX-50]].<ref name="Lindström"/>

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.<ref name="Lindström"/>

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.<ref name="Lindström"/>

===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.<ref name="Lindström"/>

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.<ref name="Lindström"/>

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.<ref name="Lindström"/>

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.<ref name="Lindström"/>

===Prototypes===
[[File:Strv103 Tanks During Field Exercises in Klagstorp, 1966 (GMSF.009705).jpg|thumb|left|Tank mobility trials in 1966]]
A spring 1957 meeting to consider the various designs resulted in "S" raising enough interest that a demonstration of its design features was needed.<ref name="Lindström"/> 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 72|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 a make a layout more similar to the S proposal.<ref name="Lindström"/>

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.<ref name="Lindström"/>

By this time, the UK had offered the latest Centurion Mk. 10, which featured the famed [[Royal Ordnance L7]] 105&nbsp;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 the very high rate of firing every three seconds.<ref name="Lindström"/> This led to the production design being given the name "Stridsvagn 103", meaning the third design mounting a 10&nbsp;cm gun.
[[File:Strv 103 in 1967 (GMSF.002303).jpg|thumb|left|An early production vehicle in 1967]]
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.<ref name="Lindström"/>

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:

{{cquote|Their new tank has advantages over our M60 in its low silhouette, lighter weight and amphibious capability. On the other hand, it is incapable of concurrent automotive movement and all-around engagement of targets. While the Army fully recognizes the advantages in the Swedish design, it considers this new tank to be more nearly a defensive tank destroyer or assault gun rather than a tank within the Army's concept of employment of tanks.<ref name="Lindström"/>}}

===Into production===
The zero-series success led to a fall 1964 production order for 70 examples.<ref name="Lindström"/> The first production examples began to arrive in 1967. These demonstrated that the original {{convert|300|hp}} [[Boeing T50]] turbine was underpowered, and a new {{convert|490|hp}} design from [[Caterpillar, Inc.|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.<ref name="Lindström"/>

===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 {{convert|240|hp}} [[Rolls-Royce K range engines|Rolls-Royce K60]] with the {{convert|290|hp}} [[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.<ref name="Lindström"/>

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.<ref name="Lindström"/>