Rodman cannon at Alcatraz

James P. Delgado.  Alcatraz.  The Story Behind the Scenery.  KC Publications, Inc., 1985,
Sixth Printing, 1998. 

A photograph from the 1860's or 1870's.  San Francisco's Telegraph Hill can be seen in the background.

Alcatraz was originally the site of a military fortification, designed to protect the United States western approaches when tensions with the Spanish were rising.  During the American Civil War, Thomas Jackson Rodman invented a hollow-cast method for casting the largest guns ever made.  In 1864, the first of four massive, 36,000 pound smoothbore Rodman guns was installed on Alcatraz island, the first on the Pacific coast.  Ultimately, in addition to a variety of other artillery pieces, the Rock had 5 mounted 15-inch Rodmans and 4 unmounted ones of this size, along with a number of smaller Rodmans.  It took 12 men to service a 15-inch cannon.  None were ever fired in anger.   They were quickly rendered obsolete. Twelve years later, on July 4, 1876, they demonstrated their antiquity.  Delgado relates:

"In celebration of the nation's centennial, the defenses of San Francisco were demonstrated in a mock battle.  The guns of many forts, including Alcatraz, were trained on various targets.  One was an explosive-filled ship that was to be destroyed in a grand finale of impressive firepower. Alcatraz's smoothbore cannon, deadly deterrents during the Civil War, proved inaccurate, as did guns of the same vintage from other forts.  The ship was finally sunk when a small boat dispatched from Alcatraz set fire to it--a fact that did not elude disappointed spectators."

Beginning in 1898, the cannon were dismounted and were gone by 1901.  Some of the gigantic cannon tubes were left on the island as decoration, but in the 1920's most were dynamited for scrap.

For more on the history of these artillery pieces, visit Rodman's Great Guns.