Low pressure breathing air compressor intended for use with airline diving equipment.
https://en.wikipedia.org/wiki/Diving_air_compressor

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Surface-supplied diving is diving using equipment supplied with breathing gas using a diver's umbilical from the surface, either from the shore or from a diving support vessel, sometimes indirectly via a diving bell.[2] This is different from scuba diving, where the diver's breathing equipment is completely self-contained and there is no link to the surface. The primary advantages of conventional surface supplied diving are lower risk of drowning and considerably larger breathing gas supply than scuba, allowing longer working periods and safer decompression.
https://en.wikipedia.org/wiki/Surface-supplied_diving#Equipm...

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Some of the skills are common to all types of surface-supplied equipment and deployment modes, others are specific to the type of bell or stage, or to saturation diving. There are other skills required of divers which apply to the surface support function, and some of those are also mentioned here.
https://en.wikipedia.org/wiki/Surface-supplied_diving_skills