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This paper describes the role of electricity as an enabling technology vital to the accomplishment of tasks underwater, i.e. subsea intervention. The basic methods of subsea intervention, i.e. ambient-pressure and atmospheric diving and the use of remotely operated vehicles (ROVs), are outlined, and the hyperbaric ambient- pressure diving environment described in some detail as this presents particular problems from the point of view of the design and operation of electrical equipment. Background information includes a brief history of the use of electricity underwater. The paper covers subsea electrical technology in general and also in relation to specific applications. General considerations include atmospheric and pressure-balanced enclosure of equipment, pressure-tolerant electronic (PTE) systems, power supplies, cables and connectors and electric safety. In the context of electric safety, the recent code of practice for the safe use of electricity underwater is summarised. Specific applications of electricity described include communications, navigation, sonar systems, underwater television and acoustic imaging, nondestructive testing (NDT), electric welding, diver heating and environmental monitoring. The consequences of, and limitations imposed by, the physical properties of water are discussed in appropriate context throughout the paper.