<P> Although Alcatraz had its own power plant, it was no longer functional, and 15 miles of cable were required to connect the island to San Francisco's electricity . As Siegel and Tuggle worked on the script, the producers paid $500,000 to restore the decaying prison and recreate the cold atmosphere; some interiors had to be recreated in the studio . Many of the improvements were kept intact after the film was made . </P> <P> The dangerous escape down the prison wall and into the water was performed without stunt doubles by Eastwood, Fred Ward, and Jack Thibeau, who had both been cast partly for their athleticism . Director Siegel twice thought they had been lost to the treacherous currents . </P> <P> The film implied that the escape had been successful . </P> <P> The character Charlie Butts is fictional . A fourth inmate, Allen West, did participate in the real escape but was left behind when he couldn't remove his ventilator grille on the night of the escape . He aided the FBI's official investigation of the escape . </P>

How much of escape from alcatraz was filmed at alcatraz