It also provided housing for the Bureau of Prisons staff and their families. During its 29 years of operation, the penitentiary claimed that no prisoner successfully escaped. A total of 36 prisoners made 14 escape attempts, two men trying twice; 23 were caught alive, six were shot and killed during their escape, two drowned, and five are listed as "missing and presumed drowned".[26] The most violent occurred on May 2, 1946, when a failed escape attempt by six prisoners led to the Battle of Alcatraz.