Electric drive is not advocated for all vessels, as its adoption can involve additional weight, complexity and cost. It can be justified where flexibility of machinery layout and operation, rapid manoeuvrability, constant-power characteristics and simple provision of power for large auxiliaries are features which can be utilised in service. Both a.c.- and d.c.-transmission systems are in use; a.c. for larger installations, and d.c. for smaller, more specialised vessels requiring the higher degree of flexibility available with this system. Reliability is the keynote in machine and control-gear design. In general, equipment is based on land practice, but machine ventilation requires special consideration. Electric drive is established as the natural choice for cable ships, icebreakers and certain types of dredger. It is in severe competition with other forms of drive for bulk-carrier, tug, trawler, ferry and passenger-vessel applications. Future technical advances in diesel-engine-governing and thyristor techniques should enable a.c. generation to be used with conversion to d.c. for propulsion and special auxiliary drives. This will greatly simplify the generation and distribution arrangements.