This report is an unclassified introduction to a model for costing of submarines in the early phases - the developed SubCost model. From historic statistic data of Swedish submarines, a deduced Submarine price index (SPI) is presented. This also includes a Quality cost index (QCI), which is applied to Swedish conditions and reflects the Swedish approach and business model. Different QCI can be set depending on relevant conditions. From these parts, three different approaches for cost estimation, prediction and calculation can be used. These three approaches are related to the three earliest phases in a development of submarines; · Before a project has started (an estimation of cost, a "guesstimate"); · During Play-Card design in the functional domain (an prediction of cost); · During concept design in the systems and installation domain (a calculation of cost). The three approaches were validated by comparison with documented data from real designs.