Richmond enjoys a very mild Mediterranean climate year round. The climate is slightly warmer than the coastal areas of San Francisco, the Peninsula, and Marin County. During World War II, Richmond developed rapidly as a heavy industrial town, chiefly devoted to shipbuilding. Its major activity now is as a seaport, with 26 million tons of goods shipped through the Port of Richmond. Chevron USA has a major oil refinery in the city. The Social Security Administration employs over 1,000 at its regional office and program service center in Downtown Richmond. Kaiser Permanente’s Richmond Medical Center hospital in Downtown Richmond is one of the largest in the city.