Fortress Alcatraz

Alcatraz's Military History 1850-1933

Fortress Alcatraz

Alcatraz's notoriety as a penitentiary overshadows its earlier, and longer, use by the Army. Surprisingly, this small island once was the most powerful fort west of the Mississippi River.

San Francisco Bay is the largest natural harbor on America's West Coast. The gold rush of 1849 turned San Francisco from a sleepy village of 300 people into a booming city - and a tempting prize for possible foreign invaders. The Army's first plans were for forts on each side of the Golden Gate, with Alcatraz as a secondary defense. However Alcatraz became a primary fort almost immediately, when there were major obstacles to building a fort on the north side of the Golden Gate.

San Francisco's first defenses, eleven cannons, were mounted on Alcatraz in 1854. By the early 1860's Alcatraz had 111 cannons. Some were enormous, firing a fifteen-inch ball weighing 450 pounds. Defenses included a row of brick enclosed gun positions called casemates to protect the dock; a fortified gateway or Sally Port to block the entrance road; and a three-story citadel on top of the island. This served both as an armed barracks and as a last line of defense.

Ironically, while built to guard against a foreign invasion, Alcatraz's most important period militarily was during the Civil War, 1861-1865. Since it was the only completed fort in the bay, it was vital in protecting San Francisco from Confederate raiders. Early in the war ten thousand rifles were moved to Alcatraz from a nearby armory to prevent their being used by southern sympathizers, The crew of a Confederate privateer were among the island's first prisoners.

There was some limited modernization of the island's defenses after the Civil War. Rifled cannons were mounted. In 1854 some 450 electrically controlled underwater mines were brought to the island to protect the Bay. However, as the ships of potential enemies became more and more powerful, the defenses were increasingly obsolete. In 1907 Alcatraz officially ceased being a fortress and became Pacific Branch, U.S. Military Prison.


Military Prison

Alcatraz Island's use as a prison began in December 1859 with the arrival of the first permanent garrison. Eleven of these soldiers were confined in the Sally Port basement. The Army recognized that the cold water (53 F) and swift currents surrounding Alcatraz made it an ideal site for a prison, and in 1861 the post was designated as the military prison for the Department of the Pacific - most of the territory west of the Rocky Mountains.

The prison population grew during the Civil War with the addition of prisoners from other army posts, the crew of a Confederate privateer, and civilians accused of treason. The Sally Port's basement was filled, then one of the gun rooms, and a wooden stockade was built just to the North of the Sally Port.

During the next three decades additional buildings were erected just north of the Sally Port to house up to 150 Army prisoners. These provided hard labor for construction projects both on and off the island. At various times "rebellious" American Indians were also held on Alcatraz. The largest group was nineteen Hopi, held in 1895.

The Spanish-American War of 1898 increased the size of the Army enormously, and the prison population also grew. A prison stockade, known as the "Upper Prison" was hastily built on the parade ground and by 1902 there were 461 prisoners on the Island. In 1904 the upper prison stockade was expanded to house 300 inmates, and the lower prison buildings near the Sally Port were used for other purposes.

With modern weaponry making Alcatraz more and more unsuitable as a fort, in 1907 the Army dropped plans to mount new guns, and instead designated the island "Pacific Branch, U.S. Military Prison." The next year, with plentiful prison labor available, work began on the Cellhouse which still stands today. Completed in 1912 with 600 single cells, each with toilet and electricity, the Cellhouse was the largest reinforced concrete building in the world.

In 1915 Alcatraz was changed from a military prison to "Pacific Branch, U.S. Disciplinary Barracks." The new name reflected the growing emphasis on rehabilitation as well as punishment. Prisoners with less serious offenses could receive training, education, and an opportunity to return to the Army. Prisoners convicted of serious crimes were not given these chances, and were discharged from the Army when their sentences were completed.

During the great depression of the 1930s military budgets were cut, and the Army was considering closing the Disciplinary Barracks - a perfect match for the Justice Departments desires for a super prison for incorrigible prisoners.

Negotiations moved rapidly, and Alcatraz was transferred to the Bureau of Prisons. By early 1934 eighty years of the U.S. Army on Alcatraz had ended - except for 32 hard case prisoners, who were left to become the first penitentiary inmates.

Last updated: November 30, 2022

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Golden Gate National Recreation Area
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