In spite of an intensive effort during these last twenty year, ocean acoustics and associated sensors and processing are still highly challenging scientific and technical issues. Reducing the cost by using components off the shelf (COTS) has permitted to address very complex problems that could not be studied with single purpose specific devices: understanding of the propagation and scattering in a shallow-water turbulent ocean environment, acoustic communication networks, improvement of detection, identification and localization of objects in the ocean. The “cheap” access to intensive processing allows increasing the automation either by refining beamforming and merging independent data or by detailed echo and shadows analysis. This paper is a presentation of the state of the art in acoustic underwater technologies for maritime applications in both mine hunting and anti-submarine warfare. The first part will deals with acoustical imaging and describes recent advances in three major areas: synthetic aperture sonar, spectral classification of echoes and portable underwater cameras. The second part is mainly concerned with passive sonar systems including both hardware and software aspects. The last part deals with acoustical communication and navigation.