[en] This study analyses the Swedish nuclear weapons research since 1945 carried out by the Swedish National Defence Research Establishment (FOA). The most important aspect of this research was dealing with protection in broad terms against nuclear weapons attacks. However, another aspect was also important from early on - to conduct research aiming at a possible production of nuclear weapons. FOA performed an extended research up to 1968, when the Swedish Government signed the Non-Proliferation Treaty (NPT), which meant the end of these production plans. Up to this date, five main investigations about the technical conditions were made, 1948, 1953, 1955, 1957 and 1965, which all together expanded the Swedish know-how to produce a bomb. The Swedish plans to procure nuclear weapons were not an issue in the debate until the mid 50's. The reason for this was simple, prior to 1954 the plans were secretly held within a small group of involved politicians, military and researchers. The change of this procedure did take place when the Swedish Supreme Commander in a public defence report in 1954 favoured a Swedish Nuclear weapons option. In 1958 FOA had reached a technical level that allowed the Parliament to make a decision. Two programs were proposed - the L-programme (the Loading Programme), to be used if the parliament would say yes to a production of nuclear weapons, and the S-programme (the Protection Programme), if the Parliament would say no. The debate on the issue had now created problems for the Social Democratic Government. The Prime Minister, Tage Erlander, who had earlier defended a procurement of nuclear weapons, was now forced to reach a compromise. The compromise was presented to the parliament in a creative manner that meant that only the S-programme would be allowed. The Government argued that the technical level did allow a 'freedom of action' up to at least the beginning of the 60's when Sweden was mature to make a decision on the issue. During this period of 'wait and see' FOA was not allowed to conduct research directed towards producing nuclear weapons. On the other hand, it was stated that it was impossible to make a clear-cut line between protection and construction research within a freedom of action. The Parliament accepted the Government's recommendation. Was then protection research the only research that was performed? The question has been under debate in the media and also the issue for one Government investigation. Former classified FOA documents have now been released and enabled this study. The conclusion of this report is that FOA went further in its efforts to make technical and economical estimations than the defined S-programme allowed, at least in a couple of instances. The findings in this report support the assumption that it was a political game that made the Swedish Government introduce the term protection research to escape criticism, while in practical terms construction research was performed in order to obtain technical and economical estimations for a possible production. A second finding of this report is that Sweden reached latent capacity to produce nuclear weapons in 1955. This is at least two years earlier than what is normally accepted in the international literature on nuclear proliferation. For example, in Stephen M Meyer's classic study The Dynamics of Nuclear Proliferation, Sweden is said to have reached latent capacity in 1957. Meyer's study refers to another study in this respect. An analysis of the declassified documents from FOA concludes that this is at least two years to late. A third aim of this report is to analyse the decommissioning of the nuclear weapons research after the NPT was signed in 1968. The fourth aim is to investigate how much plutonium, natural and depleted uranium and heavy water FOA had at its disposal within the research programme. The result of this investigation is given in appendix 2