Discover the Hidden Story of Alcatraz’s Underground Military Base

For most people, “Alcatraz” might evoke the image of an old, impenetrable prison fortress off the coast of San Francisco. A place of captivity where no one would dare to escape—uninhabitable and solemn. However, besides its history of criminal correction and military utility, researchers recently discovered that Alcatraz also houses an incredible collection of long-buried secrets. 

The island’s first intended purpose was not as a place to hold convicts—but to keep cattle. Alcatraz was given to a man named Julian Workman by Pio Pico, the Mexican governor of Alta California, on the understanding that he would build a lighthouse there to guide ships as well as his ranch.

Acting on behalf of the United States government, John Fremont, the newly installed Military Governor of California, bought Alcatraz for $5,000. Fremont expected the government to reward him with a large payout for the purchase of the island. Unfortunately, this would not come to pass.

Fremont may as well have thrown his $5,000 investment into the sea. The United States government declared that his purchase of the island was invalid since it already belonged to them. Despite his protests, he was left high and dry without so much as a “thank you.” 

The original Spanish name of the island, La Isla de los Alcatraces, roughly “ Island of the Pelicans” in English, was coined by the Spanish explorer Juan Manuel de Ayala in 1775. This lengthier name later became “Alcatraz Island” following the Mexican land cession. 

By 1853 the United States began construction of a fort on Alcatraz Island. With the Gold Rush in full swing at the time, the authorities felt the need to establish a base to keep the city secure. The promise of fortune saw San Francisco go from a population of 300 people to 30,000. 

Alcatraz Island wasn’t the only base in the area. The military dug in at Fort Point, on a neighboring island. The two locations would help the country safeguard all those new arrivals should there be trouble. The engineers went all in on the job. 

The engineers at the time knew that they were building in an indomitable location. Remarking on their tactical luck, the Pacific Coast Board of Engineers commented, “Nature seems to have provided a redoubt for this purpose in the shape of Alcatraz.”

In laying out his plans, Zealous Tower took the naturally solid foundations of the island and built upon them. Rock from the island was used to throw up great walls along the coastline, saving costs and packing the island’s defense all in one stroke. 

Not only was the fort fully stocked with cannons pointing in just about every direction that mattered, as well as offering a sheer rock face for anyone looking to scale the perimeter, but the fort also boasted caponiers—short towers that jutted out from the shoreline. 

The lighthouse wasn’t just for the safety of the nearby vessels. It was of strategic importance and, being the first of its kind, symbolic. To safeguard it, anywhere between 100 and 200 soldiers could be outfitted and deployed on Alcatraz at any given moment. 

It seems the engineers behind Alcatraz did their job a little too well and made the fort too intimidating to take on. With 350 serving men placed at the island fort, it never saw action—not even a minor conflict—all throughout the civil war. 

The final touches on Alcatraz Island took longer than planned to complete. They finally finished putting up provisions and decor in 1859. There was a scarcity of skilled laborers in San Francisco at the time. 

Today, Alcatraz Island is remembered for its prison construct rather than its military history. Interestingly, these two stories intersect as the first individuals held captive on the island were military soldiers in 1859. During the Civil War, Alcatraz housed captured Confederate soldiers.

The government soon repurposed Alcatraz to hold civilians. The first prisoners began to arrive in 1934. The island was the ideal holding pen for several reasons. First, the obvious—the prison was surrounded by a freezing cold ocean.

Alcatraz transitioned into a prison complex gradually. The fort had its own jailhouse as early as 1867, but it could only handle a few inmates. During the American-Spanish conflict, the jailhouse had expanded. The fort could hold and feed over 450 prisoners. 

On August 11, 1934, Alcatraz Penitentiary opened its doors to its inaugural cohort of prisoners, hand-picked due to their disruptive behavior at other facilities. These inmates were in for a change of pace on the remote island prison. Alcatraz’s first warden, James A. Johnston, was responsible for maintaining order among these rowdy convicts. 

With Alcatraz fully operational as a penitentiary, it soon became a hub for housing some of the United State’s most infamous figures. Names like George Kelly and Al Capone likely still ring familiar today. Alcatraz is where they ended up serving their time.

Throughout Alcatraz’s history, it was the site of 14 escape attempts. None of the prisoners who attempted to flee the island were confirmed to have reached the mainland. Six lost their lives, 23 were recaptured, and two drowned. The remaining five are “missing and presumed drowned.”

The 13th escape attempt from Alcatraz Penitentiary was truly an intriguing episode. Three convicts, John Anglin, Clarence Anglin, and Frank Morris, executed a meticulously planned breakout and braved the icy waters of the San Francisco Bay.

By the 1960s, it had become impossible to keep Alcatraz open as a penitentiary. For one, it was too costly to pay for all the inmates. Each head would cost the prison $10 a day compared to that of other prisons, which cost $3. There were additional maintenance costs, too.

Although Alcatraz is often described to have a Spanish discoverer, the island was well-known to many Native American tribes long before foreign ships arrived on the shore of the continent, a sentiment expressed by the historian Troy R. Johnson in The Occupation of Alcatraz Island.

When Alcatraz opened its doors to the public, it became a tourist destination. However, long after Alcatraz had become a popular tourist destination, the Binghamton University team, led by Timothy de Smet, had a scientific mission when they visited the island.

With their cutting-edge equipment, de Smet and his team of researchers were able to uncover something about Alcatraz without picking up a single stone or drilling through an inch of concrete. It seems the military back in the 19th century was more dug-in than many people realized.

Each traverse contained communication tunnels, as shown by the green arrows here. According to the researchers, the features of the constructions were remarkably well preserved. One of the layers sits directly below the Alcatraz Recreation Yard, separated by a thin layer of concrete.

Part of the reason for their excellent keeping might be that they were covered over in thin layers of concrete. This would likely have been done a little while after the fort’s initial construction. Here’s an image of the outside of the facility when there were still cannons still facing out to sea. 

Much of the military fort was bulldozed to make way for the prison complex. With that in mind, de Smet and the team asked whether some constructions of historical value might remain underground at Alcatraz. The non-invasive laser technology used to draw a picture of the below levels was created as a result of that question. 

While the finding of the secret Alcatraz levels is incredible in itself, the real discovery might have been the development of their laser-and-radar-based sensing technology. This innovation helped push the limits on what archaeology is capable of doing in the future.