The project Underwater Weapons Effect within the R&D program Underwater Technology concerns knowledge of the effects of underwater detonations in structures, primarily large structures, but also different infrastructure installations. The knowledge may be used for the design of warheads, predictions and assessments of effects of close-proximity charges, a posteriori investigations, reviewing requirements and reports, and proposing changes in system functionality. Project members have carried out assignments for FMV with the purpose of assessing the effect of warheads, in which a major leap towards a model library was taken. The project primarily conducts experiments using small to middle-sized targets, where the former is described as validating experiments, and the latter comprise an extended complexity in both experimental setup and for measuring the dynamic response. A priority for the project is to validate a numerical code, describing the advantages and disadvantages of the code, with the purpose of increasing the confidence in that the code predicts the effects of an underwater detonation. In target structures, materials, often steel, are found and must be characterized for every new steel batch used in experiments. The characterization results in a material model with model parameters. It is of particular interest to relate these material models to the computational mesh, since the mesh itself rarely can be made sufficiently fine to correspond to tensile tests. The project also studies simplified models, and what predictions these allow for underwater charges. A trilateral collaboration, SNAP-CPU (Survivability of NAval Platforms - Close Proximity UNDEX), with the DRDC (Canada) and the TNO (the Netherlands) have recently been concluded. A renewed collaboration will start 2025.