Naval operations in coastal waters are a huge challenge for modelling support in several disciplines. For example, any decision dependent on sonar performance could be depending on a proper translation of input from a reliable oceanographic model, that relies itself on reliable input from a meteorological model. Obvious to mention that many things can go wrong, and it is not surprising that there are not many examples for the complete information chain; from scratch or climatology to final operational interpretation and decision. During the MREA-04 exercise near Lisbon, in an attempt to complete the abovementioned chain, sonar range forecasts were provided based on the oceanographic fields provided by the Harvard Ocean Prediction System (HOPS). These fields are fourdimensional (xyz-t), or, in terms of operational sonar modelling: at any time, in any direction, providing range-dependent sound velocity profiles. This was used to model performance of a low frequency active sonar (LFAS) system, common in Anti- Submarine Warfare (ASW). At three hypothetic ship positions, the (simplified) sonar performance was provided in near real-time. This procedure can easily be extended for any ship’s track.