Not Much Defense Needed
People got to make use of Fort Alcatraz when the Civil War in the United States was happening. Sources say that there were about 350 men stationed on the island. Unfortunately, they were not so productive then since no one made attempts to take over the fort.
The Confederate army had a plot planned, but they never pushed through with it. There were only three men who faced arrest in 1863 in an attempt to attack the fort, but they had an unserved sentence of about ten years. It’s because the late Abraham Lincoln gave all of them a pardon after the war.