A guide and guard book for the professional diver, for doctors and directors of underwater operations, for the advanced, expert nonprofessional, has been translated from the French and offers basic laws of the underwater world and necessary precautions for accident prevention. The effects of pressure, facts of weight and vision and sound are the physical concepts applied to diving; next comes apparatus and equipment (dress and breathing mechanisms, protective clothings and air supply). This is followed by a survey of diving accidents and the physiology of diving, diving tables and their computation, breathing mixtures, free diving and underwater photography. The accidents section includes occupational disorders and gives causes, symptoms, prevention and treatment, from merely discomfort to grave dangers. From members of the Undersea Research and Development Group of the French Navy this safety counsel carries authority that would profit any novice, even if its field is primarily specialized.