Alcatraz is located in San Francisco Bay. The island was originally developed to defend the bay, but was quickly used as a military prison. In 1934 the island was transferred to the Department of Justice and designated a Federal Penitentiary. During it's 29 years as a federal prison 36 men tried to escape. 5 of those men were never found. Is it possible that they escaped?
This video gives an overview of all 14 escape attempts, with more details on some of the more interesting attempts. Prison authorities maintain that no one ever successfully escaped from Alcatraz, but the evidence shows that it is possible.