This section deals with the more specialized equipment used by professional and military divers, as well as some recreational technical divers. Many of the military diver’s tasks, and some of those of the professional diver, involve comparatively shallow depths. Such tasks could be conducted with scuba gear of the type described earlier. Equipment fitted with communication devices allows the diver to confer with the surface support. Communication devices operate better in air, so they are commonly fitted into a helmet or full-face mask. In these devices, the airflow may either be continuous or on demand.
More specialized equipment is used for some military diving where an element of stealth is required. For these tasks, an oxygen rebreathing system that can be operated with no telltale bubbles may be used. In dealing with explosive mines, stealth is again required to avoid activating the noise- or magnetically triggered circuits. If the mine may be too deep for an oxygen set, a rebreathing system with an oxygen-nitrogen mixture may be used.
For even deeper tasks, for which oxygen-helium mixtures are used, some method of reducing the gas loss gives cost and logistical savings. This can be achieved by the diver’s using a rebreathing system or returning the exhaled gas to the surface for reprocessing.