Oh man, it's my dream question. This is my one and only real area of expertise, so please, ask me everything about the strv 103. I know way too much about that thing. I love explaining how it works, it's an amazing piece of technology.

The answer that will follow is mostly based on my own original research in the formerly classified development documentation kept at the National Military Archives - even the most ambitious books on Swedish AFV developments don't do a great job of explaining the strv 103 and its peculiarities. I've been working on an internet argument essay with the tentative title "The Stridsvagn 103 Was Not A Tank Destroyer" for a while, and this answer is in part based on that. So, here goes.

Introduction
In internet arguments, it is frequently claimed that the stridsvagn 103 (strv 103, "S-tank") was a defensive tank, or basically a tank destroyer. It was, claims the common wisdom (perpetrated by places like History Channel), meant to dig down in a forest, take a few shots at attacking Soviet tanks and then retreat, using its rear driver to its advantage. Even in the Swedish army, some officers (although mainly ones who had no experience on the tank) thought it was worthless for traditional tank work - that is, offensive tasks. I will show that this is simply not true: the Swedish army set out to figure out how to build a good tank, came up with the S-tank idea, developed and built that idea as a tank, which it then proceeded to use operationally as a tank.

The origins of the strv 103, or "alternative S"
In 1957, the Swedish army initiated a study of the future of warfare, in order to determine what weapons technology it should pursue during the 1960's (as well as many other things). One of the sub-committees of this study was tasked with studying direct-fire infantry support weapon systems (such as tanks, anti-tank weapons, direct-fire crew-served weapons, etc). The central question that the sub-committee was tasked with answering was: "How should our system for direct fire (both anti-tank and anti-personnel fire) work around 1970 and in the time immediately thereafter?" ^1

Additionally, the committee was asked four more specific questions, two of which had to do with tanks. First, it was asked to draw up technical requirements for a new tank to be in service around 1965, and while doing so investigate the appropriate trade-off between firepower, speed and protection - perhaps more than one type of tank would be needed? Second, it was asked to study how tanks were to be integrated into the army organization, keeping in mind the requirement to be able to quickly concentrate strong tank formations that would allow attacking strategically important locations such as a hostile beachhead, and in connection to this recommend a minimum number of tanks required in the entire army. Here, it is already becoming apparent what the army was thinking about tanks.

As a part of its work, the committee naturally kept tabs on foreign design trends. It appeared that there were two main schools of tank design thought in the West: one Anglo-American and one French-German one. The Brits and the Americans, the committee found, were intending to develop heavier tanks (around 45 tons - this trend would materialize as the Chieftain and the M60) with more armor, while the Germans and the French were aiming at lighter and faster tanks (around 30 tons, which would materialize as the Leopard I and the AMX-30) - the latter school thought that it would be impossible to combine decent mobility with enough armor to protect against the constantly improving HEAT rounds of the period. For comparison purposes, these hypothetical tanks were designated the "A-tank" and the "T-tank" respectively, where A stood for America and T for Tyskland (the Swedish word for Germany). Additionally, it also studied a newly invented Swedish concept (patented in 1956 by an engineer at the Army Ordnance Administration, Sven Berge), consistently enough named the "S-tank". The S-tank concept lacked a turret and had a two-man or possibly even one-man crew, and because of this it could be designed with extremely well sloped front armor which would protect against the kinetic armor-piercing rounds of the period. The turretless design also allowed for a standoff screen in the front of the tank for protection against HEAT rounds. In short, it could potentially offer the protection of the A-tank with the same low weight and power-to-weight ratio as the T-tank - and low weight was considered important for strategic mobility reasons (easier to find railroad cars that could transport the tank and bridges that could support its weight).

After conducting a number of sub-studies (on things like the probability of victory in hypothetical duels between the three alternatives above, the effects of nuclear radiation on tank crews, the development of IR night vision devices, and war games involving tank assaults into beachheads) the committee delivered its report in May 1958. In regards to tanks, it recommended that development should be a started on a well armored tank much like the A-tank, and that development in the UK and the US should be monitored and the possibility of buying a design from either country be kept open. However, the committee also found that "alternative S" was interesting enough to merit further study, and recommended that some feasibility trials be conducted, at a limited scale. Furthermore the committee also found that newer, better tanks should be organized into armored brigades capable of attacking an opponent in open terrain, while older tanks should be assigned to direct infantry support only, in anti-tank companies in the infantry brigades.

It is already apparent where we're heading: the army concluded it needed a tank for its armored brigades, and the role of the armored brigades was an offensive one - counterattacking a beachhead being the typical example of an operation such a brigade might carry out. The S-tank was conceived as an offensive weapon, considered equal in role and performance to the foreign tanks then in development.

The development process
As the committee recommended, so were it to be, and initial work on some S-tank test rigs was contracted to Bofors in 1958. The development at this early stage was focused on a 30-ton two-man tank with a conventionally elevating gun, fed by an autoloader using two-piece ammunition (the "A-tank" proposal that was under development at the same time was to use the same gun and ammunition). By March 1959, however, the army had changed its mind, for several reasons. Experiments with two-man crews in other armored vehicles at the Armored Forces School had found that just driving, spotting and firing was so taxing on the crew that it left no mental resources over to manage communication with the rest of the unit, especially not if the commander also had to handle a secondary weapon, such as a machine gun or an autocannon. Consulting German war veterans at the West German armor school in Munster about their experiences pointed in the same direction: two men simply weren't enough, especially not with the complex radio equipment in use in the late 50's. Autoloaders were not entirely trusted either; it seemed like it would be a good idea to have someone who could monitor it and fix potential jams. A third crew member was necessary, and finding space for him would increase the weight of the tank. However, it seemed that this could be solved by returning to Sven Berge's original gun elevation idea, more or less as envisioned in his 1956 patent. By fixing the gun in the chassis in the vertical axis too and instead elevating by moving the road wheels, the autoloader mechanism could be moved to the rear of the tank, where the would also be room for the third man. From there, the step to giving him too a set of controls was not big - reversing in a tank is ordinarily quite difficult and usually involves a guide on the outside of the vehicle since the driver has zero visibility to the rear - and thus the rear driver/radioman was in place. ^2

The various trials were mainly positive - the concept was found to be workable in practice, and the A-tank development was put on hold. A prototype series of 10 S-tanks was ordered in 1960 - the positives seemed to by far outweigh the negatives already at this point, but further studies were conducted. In 1961, the Armored Forces School investigated the possible downsides of a lack of gun stabilization and an inability to engage targets that were not directly in front of the tank. The study stated that at the time, even in tanks with stabilization, firing on the move at distances greater than 500 meters was mostly a waste of ammunition. Even at shorter ranges only big targets (i.e. tanks) were to be fired at on the move. According to the study, the main benefit of stabilization was taking 2-3 seconds off of the time between stopping and opening fire. With this in mind, as well as the fact that in the S-tank it would be possible for the commander to take over control and show the gunner/driver a spotted target, it is easy to see why the study concluded that it could not see why the S-tank would be inferior in reaction time to a turreted tank. The ability to easily and quickly retreat with the front armor towards the enemy (thanks to the rear driver) was also considered an advantage. ^3

By 1961, the army HQ was calling for at least 200 new tanks, preferably with deliveries starting in 1965. The debate regarding which tank to buy would continue into 1962 - the S-tank was compared to both other Western tanks of the time and estimates of the Soviet adversary tanks in a number of simulations and paper wargames. The conclusion was that while the Chieftain was good, the S-tank was better - it was estimated to have very similar protection but was much lighter and presented a smaller target. ^4

Great write up and read! Now we finally have something to put the whole "tank destroyer" argument to rest with!

Just a couple of questions:

one in Skövde on the big plains in the southwestern part of the country where a lot of important air force bases were located, and where it could easily reach the important harbor in Gothenburg.

Interesting. I assumed Skaraborgsbrigaden was to launch a counter-attack against a bridgehead in the Bråviken area and/or an airborne landing on Närkeslätten (south of Örebro). Did the military believe that Gothenburg was a potential target for a bridgehead, considering the enemy would have to pass through the Öresund straits to get there?

Three of the seven armored brigades had their initial positions in the provinces of Skåne and Blekinge

P2, P4 and P7, which I assume are the three regiments/brigades you're refering to, were/are all located in the Skåne region. Or is it me that's missing some regiment?

Fairly minor points in the scale of things though. Thank you for taking the time to write this!

Awesome answer by Renhanxue I look forward to more responses from him about cold war Sweden!!!