Military prison[edit]
Main article: Alcatraz Citadel
Because of its isolation from the outside by the cold, strong, hazardous currents of the waters of San Francisco Bay, Alcatraz was used to house Civil War prisoners as early as 1861.
Following the war in 1866, the army determined that the fortifications and guns were being rapidly rendered obsolete by advances in military technology. Modernization efforts, including an ambitious plan to level the entire island and construct shell-proof underground magazines and tunnels, were undertaken between 1870 and 1876 but never completed (the so-called "parade ground" on the southern tip of the island represents the extent of the flattening effort).[20] Instead, the army switched the focus of its plans for Alcatraz from coastal defense to detention, a task for which it was well suited because of its isolation. In 1867, a brick jailhouse was built (previously inmates had been kept in the basement of the guardhouse), and in 1868, Alcatraz was officially designated a long-term detention facility for military prisoners. The facility was later discontinued for POW's in 1946. Among those incarcerated at Alcatraz were Confederates caught on the West Coast,[6] and some Hopi Native American men in the 1870s.[21]
In 1898, the Spanish–American War increased the prison population from 26 to over 450, and from 1905 to 1907 it was commanded by George W. McIver. After the 1906 San Francisco earthquake, civilian prisoners were transferred to Alcatraz for safe confinement. On March 21, 1907, Alcatraz was officially designated as the Western U.S. Military Prison, later Pacific Branch, U.S. Disciplinary Barracks, 1915.[18] In 1909 construction began on the huge concrete main cell block, designed by Major Reuben Turner, which remains the island's dominant feature. It was completed in 1912. To accommodate the new cell block, the Citadel, a three-story barracks, was demolished down to the first floor, which was actually below ground level. The building had been constructed in an excavated pit (creating a dry "moat") to enhance its defensive potential. The first floor was then incorporated as a basement to the new cell block, giving rise to the popular legend of "dungeons" below the main cell block. The Fortress was deactivated as a military prison in October 1933 and transferred to the Bureau of Prisons.[18]
During World War I, the prison held conscientious objectors, including Philip Grosser, who wrote a pamphlet entitled Uncle Sam's Devil's Island about his experiences.[22]