The Battle of Alcatraz: Two Days of Violence

In May 1946, six desperate inmates at America's most secure prison executed what should have been impossible: they overpowered nine guards, seized weapons from the gun gallery, and held Alcatraz at gunpoint for two days. The federal government responded with Marines, bazookas, and grenades.Bernard Koy, a library orderly, had spent months studying security flaws in "The Rock." On May 2nd, he and five accomplices systematically subdued guards, freed violent criminals from their cells, and armed themselves. But when they couldn't find the key to the recreation yard—their path to freedom—desperation turned to violence. What began as a calculated escape became a pitched battle that shook the foundations of America's prison system.The Battle of Alcatraz remains the deadliest prison escape attempt in American history. Three inmates and two guards died in the fighting. Seventeen others were injured. The two-day siege exposed vulnerabilities in the nation's "escape-proof" fortress and led to permanent security reforms that reshaped federal prison operations.Subscribe to Hometown History for forgotten American history stories every week. New episodes release Tuesdays. Every hometown has a story—what's yours?In This Episode:How a library orderly named Bernard Koy identified critical security flaws in America's most secure prisonThe moment six inmates overpowered nine guards and seized control of Alcatraz's gun galleryWhy a single missing key (#107) turned a calculated escape into a two-day armed battleHow the US Marines brought bazookas and anti-tank mortars to storm their own federal prisonThe execution of two surviving masterminds and the surprising redemption of 18-year-old Clarence KarnesKey Figures:Bernard Koy - Library orderly and escape mastermind; discovered vulnerabilities through freedom of movementJoe Kretzer - Experienced escape artist who helped plan the operation; killed in final battleSam Shockley - Psychologically unstable inmate; executed 1948Marvin Hubbard - Armed accomplice; killed in battleClarence Karnes - Youngest participant at age 18; later paroled after becoming model prisonerMirin Thompson - Prior murderer; executed 1948 for role in guard killingsCaptain Harry Winehold - Former Marine who charged into D-Block; shot and wounded in attempted rescueHarold Stites - Guard who led rescue team into gun gallery; killed in gunfire exchangeTimeline:May 2, 1946, 1:30 PM: Koy initiates plan by subduing Officer Bill Miller in the kitchenMay 2, 1946, ~2:00 PM: Inmates seize control of gun gallery and distribute weapons to accomplicesMay 2, 1946, 2:07 PM: Main prison alarm activated after guard stations fail to respondMay 2-3, 1946: Two-day armed standoff; Marines deploy grenades, bazookas, anti-tank mortarsMay 4, 1946, 9:40 AM: Guards discover bodies of Koy, Kretzer, and Hubbard (gunshot wounds to head)December 3, 1948: Sam Shockley and Mirin Thompson executed via gas chamber at San Quentin1973: Clarence Karnes paroled after transformation into model inmate and prison chess championAftermath: The battle forced immediate security reforms at Alcatraz, including stricter work procedures and enhanced guard protocols. Despite these measures, escape attempts resumed within a decade. In 1962, Frank Morris and the Anglin brothers executed the only potentially successful escape from Alcatraz (their fate remains unknown). The violen