Alcatraz - Military History

The earliest recorded owner of the island of Alcatraz is one Julian Workman, to whom it was given by Mexican governor Pio Pico in June 1846 with the understanding that the former would build a lighthouse on it.
Julian Workman is the baptismal name of William Workman, co-owner of Rancho La Puente and personal friend of Pio Pico. Later in 1846, acting in his capacity as Military Governor of California, John C. Fremont, champion of Manifest Destiny and leader of the Bear Flag Republic, bought the island for $5000 in the name of the United States government from Francis Temple.

In 1850, President Millard Fillmore ordered that Alcatraz Island be set aside specifically for military purposes based upon the U.S. acquisition of California from Mexico following the Mexican-American War. Fremont had expected a large 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 (1848) which ended the Mexican-American War, 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 San Francisco Bay. In 1853, under the direction of Zealous B. Tower, the Corps of Engineers began fortifying the island, work which continued until 1858, eventuating in Fortress Alcatraz. The island's first garrison at Camp Alcatraz, numbering about 200 soldiers and 11 cannons, arrived at the end of that year. When the American Civil War broke out in 1861 the island mounted 85 cannons (increased to 105 cannons by 1866) in casemates around its perimeter, though the small size of the garrison meant only a fraction of the guns could be used at one time. At this time it also served as the San Francisco Arsenal for storage of firearms to prevent them falling into the hands of Southern sympathizers. Alcatraz never fired its guns offensively, though during the war it was used to imprison Confederate sympathizers and privateers on the west coast.