The organisation of the technical maintenance both of manned and automatic lights is centred at Wellington, with depots at Auckland, Picton, and Bluff. The New Zealand Light Service is unusual in that all manned lights are electrified, where possible from the national mains supply, and otherwise with diesel-electric generating plant. As this allows for the use of electric alarm bells which cover all types of failure, the system is preferable to that of watchkeepers, as required for kerosene incandescent lights used in many other countries. The automatic light beacons are equally divided between electric lights of mains or battery operation and acetylene gas lights. Where road access is possible, replenishment of batteries or gas bottles is carried out by truck and, in one remaining case, by pack horse. Those lights which are on inaccessible coasts or islands are maintained from the sea by Marine Department vessels in the Cook and Foveaux Straits, Auckland, and Marlborough Sounds areas.