Alcatraz Island is the island in the San Francisco bay on which a fortress was constructed in the mid-19th century. Shortly afterwards, the fortress was converted into a famous and notoriously escape proof prison to hold prisoners of war. After the 1906 San Francisco earthquake, it was used to house civilian prisoners.
There has been only one successful escape from Alcatraz. The prisoners constructed papier-mâché heads, including real hair clippings which they collected during their visits to the prison barber. A utility corridor that was seldom used ran behind all of their cells. They used tools such as spoons to chip away at the walls and built false walls to conceal the damage. They gained access from it to the roof of the cellblock by removing fans from an air vent, using grilles carved from bars of stolen soap to hide the exit, and used the corridor to build a raft six feet wide and fourteen feet long out of fifty prison-issued rubber raincoats.
On the day of the escape, they put the dummy heads in their beds, collected their raft and the paddles and lifebelts they had built, took everything up to the prison roof through the air vent, then climbed down the side of the building and went to the edge of the sea. They used a stolen concertina to inflate the raft, and set off. They were never seen again. One dead body in prison uniform, impossible to identify, was found some months later, but there is no evidence for either the death or survival of the other two.