Alcatraz Island 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
Alcatraz Federal Penitentiary as it was conjectured that they drowned in the bay and their bodies swept out into the sea due to the turbulent bay currents. The most violent escape attempt occurred on May 2–4, 1946, when a failed attempt by six prisoners led to the Battle of Alcatraz, also known as the "Alcatraz Blastout". It was carried out by six prisoners; Bernard Coy, Joseph Cretzer, Sam Shockley, Clarence Carnes, Marvin Hubbard and Miran Thompson. They daringly took control of the cell house by overpowering correctional officers, and were able to enter the weapons room, where they then demanded keys to the