The character of Dan Durando is the only one of the escapees that is fictional. The actual sixth member was Clarence Carnes, a Native American who was spared execution because he refused to kill the captured prison guards as ordered, although he was given an additional life term.
This film was originally set to have been made several years earlier, starring Glenn Ford, Ernest Borgnine and Stacy Keach. Richard Lang was to have been director.
The film depicts only 6 men getting out of their cells and trying to escape. In fact, almost 30 inmates were freed from their cells, but returned when they were unable to open the door of the cell house.
The General Merrill portrayed in this film, and who did really participate in this Battle of Alcatraz, was the famous Frank Dow Merrill (1903 -1955) of the Merrill's Marauder's fame. These men formed the 5307th Composite Unit, a long-range penetration jungle warfare group of the United States Army. They soldiered in the Southeast Asian theatre during the Second World War.
David Morse, who plays Marvin Hubbard, later appeared in A Rocha (1996) as Major Tom Baxter, a U.S. Marine who is part of a team that takes over Alcatraz prison.