The suitability of sound waves as a carrier of information in the ocean is known to be highly variable. In the past, the assessment of the controlling environmental parameters has typically been subject to post-cruise analysis and often took years. SACLANT Undersea Research Centre and NATO’s organization for military oceanography agreed upon a three-year series of surveys in the Mediterranean Sea aimed at the development of a methodology for rapid environmental assessment (REA). A large number of research ships and patrol aircraft were provided by various nations. Researchers of numerous institutes were engaged in the REA trials. Time-invariant parameters such as bottom properties were measured directly or determined by inversion. The results were transferred for optional replacement in a standard database. Time-dependent parameters such as the sound velocity structure were predicted by means of real-time ocean models initialized and updated with survey data. The infrastructure for timely delivery of REA products and forecasts was developed, the main requirements being appropriate data channels and data fusion capacity. Rapid response was the first demonstration by the research community that the critical characteristics of the acoustic environment can be provided by the end of a mission.