The movie is set in 1943. The lighthouse keepers are depicted as members of the U.S. Lighthouse Service. The Lighthouse Service was disbanded on July 7, 1939. At that time, all lighthouse functions were assumed by the U.S. Coast Guard. Lighthouse personnel in 1943 would have U.S. Coast Guardsmen.
Early in the film, Champ and Jimbo are shown reading a newspaper which describes the current news about the war. At Alcatraz, newspapers were not allowed. All news was announced to the convicts solely at the Warden's discretion. Major events like the attack on Pearl Harbor were announced, however convicts generally didn't get a daily update on the events of the war.
The film shows the prison industries at Alcatraz shutting down due to supply shortages caused by the war. In reality, all of Alcatraz's industries were busier than ever during wartime. Most of their production was geared towards helping the war effort. Alcatraz's shops produced items like scrambling nets to be used during amphibious assaults, rubber mats for the sides of ships, etc. And, the prison's laundry services was the place local Army and Navy bases sent their soiled items. Alcatraz even received a citation for the contribution to the war effort it provided. (The convicts were actually enthusiastic workers as they were completely behind the war effort. There were even reports that when Navy ships passed close to the island, convicts in the exercise yard would cheer at the ships.)
In the film, Champ and Jimbo are depicted as being cellmates. At Alcatraz, the policy throughout the prison's entire twenty-nine year history was that each cell housed only one man. Nobody ever had a cellmate. After the 1946 Battle of Alcatraz rendered large portions of "C" Block uninhabitable, the affected convicts were either temporarily transferred to the unused and antiquated "A" Block or transferred to another prison entirely. This was solely due to maintain the one cell/one man rule.