Alcatraz Island the hands of Confederate sympathizers. Alcatraz, built as a "heavily fortified military site on the West Coast", formed a "triangle of defense" along with Fort Point and Lime Point, and ensured security to the bay. The island was also the site of the first operational lighthouse on the West Coast of the United States. Alcatraz never fired its guns offensively, though during the war it was used to imprison Confederate sympathizers and privateers on the west coast. Because of its isolation from the outside by the cold, strong, hazardous currents of the waters of San Francisco Bay, Alcatraz was used
Alcatraz Citadel compensation for his initiative in purchasing and securing Alcatraz Island for the U.S. government, but the U.S. government later invalidated the sale and paid Fremont nothing. Fremont and his heirs sued for compensation during protracted but unsuccessful legal battles that extended into the 1890s. Following the acquisition of California by the United States as a result of the Treaty of Guadalupe Hidalgo which ended the Mexican–American War (1848), and the onset of the California Gold Rush the following year, the U.S. Army began studying the suitability of Alcatraz Island for the positioning of coastal batteries to protect the approaches to