The Portsmouth was an important ship during the Mexican-American War, when her crew liberated the town of Yerba Buena, whose name was changed to San Francisco in 1847. She set sail on 25 January 1845 from Norfolk, Virginia, on a cruise around Cape Horn to join the Pacific Squadron under the command of Commodore John D. Sloat. En route, she made stops in Rio de Janeiro, Valparaiso, Callao, the Sandwich Islands, and Acapulco. To prevent the possibility of Great Britain acquiring California, she was initially engaged in protecting San Francisco Bay by watching the movements of British vessels off the California coast. After the declaration of war with Mexico, a detachment of Marines under the command of Second Lieutenant Henry Bulls Watson rowed ashore and raised the American flag over Yerba