The diving helmet is a rigid head shell and breathing gas supply used in underwater diving. They are mainly worn by professional divers engaged in surface diving, although some models can be used with diving equipment.

The diving helmet isolates the whole head of the diver from the water, so that the diver can clearly see the underwater, provide breathing gas for the diver, protect the diver’s head during heavy or dangerous work, and usually communicate with other divers on the water.

Source: @a_ron_crubbard