Union Steam Ship Company of New Zealand Limited was once the biggest shipping line in the Southern Hemisphere and New Zealand's largest private-sector employer. It was incorporated by James Mills in Dunedin in 1875 with the backing of a Scottish shipbuilder, Peter Denny. Bought by shipping giant P&O around the time of World War I it was sold in 1972 to an Australasian consortium and closed at the end of the twentieth century.