Abstract: In recent times, we have been observing a significant development of acoustic methods in underwater research. At the same time, we have easier and cheaper means of access for acoustic sensors to survey with a greater detail and more precise positioning of underwater objects. Recently, detailed investigation of underwater military, but not only the applications, has involved state-of-the-art technologies. Detection and examination of the shallow as well as deep underwater areas, using advanced technologies, have opened a new era in the ocean science. The human-operated vehicles, remotely operated vehicles and autonomous underwater vehicles have been employed for this purpose with great success. A new method of underwater observations, namely the acoustic time reversal method, has been applied in ocean investigations.