US military bases have a tradition of producing some of the world’s finest soldiers. But as threats fade and new ones emerge, and technology moves on, some of these bases become obsolete and are decommissioned. Some find new purpose in the civilian world, while others are left abandoned to the elements.

Click through this gallery to discover America’s eeriest deserted military bases and the secrets they hold...

Fort Jefferson in the Florida Keys began construction in 1846 and was intended to help protect American shipping lanes in the Caribbean from piracy and enemy attack. The sturdy, six-sided brick walls protected living quarters where soldiers and equipment were stored, surrounded by a moat. When the American Civil War started the fort was used as a prison – mainly for Union deserters. Today it is part of the Dry Tortugas National Park and remains the largest masonry structure in the Americas, covering 16 acres.

When it was built in 1942 to protect America’s East Coast from possible attack by Nazi Germany, the Cape May Bunker sat on high ground 900 feet (275m) or more from the waterline and was covered in sod to blend in. Today it sits abandoned and exposed, the changing tides washing against the sturdy wooden pilings it sits on. The round concrete turrets on either side once housed six-inch guns, but these days the emplacement is neither safe to visit nor easily accessible.

The Stanley R Mickelsen Safeguard Complex in Nekoma, North Dakota was the United States' only operational ABM (anti-ballistic missile) defence system, designed to intercept and destroy incoming Russian missiles. While it was operational for less than a year, its very existence encouraged the Soviets to sign the Anti-Ballistic Missile Treaty in 1972, which led to a decline in Cold War tensions. Despite costing $6 billion (£5.3bn) to build, the underground complex was flooded when the site closed, with only the rather eerie launch pyramid still visible.

Love this? Follow us on Facebook for travel inspiration and more

Fort Ord is a former United States Army post on Monterey Bay on California’s Pacific coast. It was primarily a training centre, and as many as 1.5 million soldiers passed through the base from the beginning of the First World War through to Operation Desert Storm in 1991. The base was closed in 1994, and in 2012 President Obama proclaimed the land the Fort Ord National Monument. Many of the buildings on the base remain standing, including the old morgue (pictured), and are popular with urban explorers.

Fort Tilden was established in Queens in 1917 to protect the entrance to New York Harbor, its giant cannons pointing towards the sea, ready for action. Despite being reinforced with concrete during the Second World War the fort never saw action and was eventually decommissioned in 1974. It is now run by the National Park Service and offers athletics fields and hiking trails, plus plenty of abandoned buildings to explore. Clamber atop the historic battery and you’ll be rewarded with panoramic views of Jamaica Bay and the Manhattan skyline.

The Devil's Slide Bunker on the shores of San Mateo County in California is what's left of a triangulation station and observation site that saw use during the Second World War, and was once part of a much larger complex of buildings. The entire site was abandoned in 1949 and today a solitary bunker remains atop the promontory. It's now privately owned, but that has not stopped graffiti artists from tagging the edifice.

More of America's most unusual abandoned attractions

This hexagonal fort in the middle of the Patapsco River just south of Baltimore was started in 1848 but never completely finished. Robert E Lee, the future commander of the Confederate Army in the American Civil War, supervised the project for a time but grew impatient and accepted a position at the West Point military academy in 1851. In 1864, heavy rains flooded the island showing that it was unsuitable for storing weapons, and in 1920 it was abandoned. Today the only visitors are urban explorers and the birds that nest in the fort's trees.

Tucked 720 feet (220m) into the hillside below the swanky Greenbrier resort, just outside White Sulphur Springs in West Virginia, lies a heavily reinforced bunker that was built between 1958 and 1962 to house Congress in the event of a nuclear war. When its existence was exposed by The Washington Post in 1992 it was decommissioned and used as a data storage facility. Safeguarded by gigantic blast doors and layers of concrete, part of the decommissioned bunker can now be visited as part of a 90-minute tour.

More incredible top-secret bunkers from around the world

The Bong Air Force Base in Wisconsin is the US military base that never was. It was abandoned in 1959 just three days before concrete was to be poured for a 12,500-foot (3,800m) runway. A heating plant was one of the few buildings completed, and you can see it here with Colonel Charles E Lancaster, commander of the base. At the time of cancellation, four years of work and more than $29 million (£22.8m) had gone into the project. Today the site forms the Richard Bong State Recreation Area, a popular fishing and hiking spot. The gravel runway is still visible.

Built between 1819 and 1826 to defend the city of New Orleans from invasion by sea, Fort Pike now lies abandoned overlooking the narrow channel of the Rigolets. During its chequered history it held up to 400 garrisoned soldiers and plenty of prisoners, including more than 1,000 Indigenous Seminole people and their allies during the Seminole Wars in the 1830s. Over the years the fort has been devastated by storms, including hurricanes Katrina and Isaac, and the damage mixed with budget cuts mean that it's currently closed to the public.

101 abandoned places left to rot across America

Set in the Bering Sea at the far end of Alaska's Aleutian Islands, the Adak Army Airfield was built in 1942 to counter the Japanese-controlled base at Kiska Harbor, situated in the same island group. Directly opposite eastern Russia, it was also an important base during the Cold War, but after the Soviet Union fell so too did the Adak base. It was decommissioned in 1997 and in 2004 the 47,271-acre site was transferred to the Aleut Corporation, a local Indigenous organisation, and the Alaska Department of Transportation and Public Facilities.

Known as 'the Gibraltar of the Chesapeake', Fort Monroe was built between 1819 and 1834 to guard the entrances to Chesapeake Bay and Hampton Roads. It is the largest stone fort ever built in the US and has a storied history, running from the Civil War into the 20th century. The fort was visited by no fewer than 14 American presidents, stretching from Andrew Jackson in 1829 all the way through to Harry Truman. Some of them, including Abraham Lincoln and Ulysses S Grant, are said to continue to visit in ghostly form. The ghost of Edgar Allen Poe is apparently spotted too – he was stationed at the fort in 1828 as an artilleryman.

Chanute Air Force Base is a decommissioned United States Air Force facility about 110 miles (180km) south of Chicago. It began as a pilot training school towards the end of the First World War, and before its closure in 1993 it was one of the oldest Air Force facilities in the country. Since then, buildings like the former mess hall (pictured) have lain abandoned, although in 2006 much of the base was placed on the National Register of Historic Places.

Check out America’s eeriest abandoned castles

Another base that started life as a First World War pilot training facility, Carlstrom Field in Florida covered 700 acres and boasted 14 hangars, with a total of 90 different structures and buildings. In 1947 it became the G Pierce Wood Memorial Hospital, a controversial psychiatric hospital, which closed in 2002. The hospital continued to use many of the military buildings, with several hangars finding work as maintenance buildings. The site was sold to developers in 2014, and nothing remains of the airfield besides a plaque.

Constructed between 1897 and 1901 to defend the shores of south Baltimore, Fort Armistead was operational for less than two decades after most of the artillery was removed for use overseas when the United States entered the First World War in 1917. Today the fort serves as a local park, with its sturdy fortifications engulfed by nature and vast quantities of graffiti. Head to the Battery Irons Entrance (pictured) to explore its eerie tunnels... if you dare.

Fort McClellan was an army base in Alabama that opened in 1917 and closed in 1999 as part of the Base Realignment and Closure programme. It was a massive training camp during the Second World War, training almost half a million troops over the course of the war, and served as a prisoner of war camp. At various points it housed the Military Police Corps, the Women's Army Corps and the Chemical Corps, and when the base was decommissioned contamination from chemicals and smoke training had to be cleared up. Much of the land has now been repurposed, although concern lingers that some people who served there may have been exposed to low levels of hazardous chemicals.

Fort Worden is one of five seacoast fortifications started in the Puget Sound region in 1897 to protect the navy base at Bremerton. At its height it boasted 41 guns mounted in 12 batteries, and it was an active military installation until 1953. In 1973 the base was turned into a multi-use state park with long empty beaches, a picturesque lighthouse and spooky old military batteries to discover. Battery Kinzie (pictured), built to house artillery but now covered with moss, is perhaps the most interesting to explore.

Check out these awesome abandoned movie sets

Fort Snelling sits on the bluffs overlooking the confluence of the Minnesota and Mississippi Rivers. Completed in 1825, the fort became notorious prior to the Civil War when soldiers stationed there were allowed to bring enslaved people with them, even though slavery was prohibited in the surrounding territory. The famous Round Tower (pictured), one of the first buildings to be constructed, remains an impressive sight. Local lore holds that Count Ferdinand von Zeppelin, founder of the Zeppelin airship company, launched his first balloon flight from the top of the tower while staying there as a German military attache during the Civil War. There is sadly no evidence to support this claim.

Deep in the heart of rural eastern Washington, you’ll find what’s left of three Cold War missile silos that once housed Titan I nuclear ICBMs (intercontinental ballistic missiles). The Titan I programme was only operational for three years (between 1962 and 1965) before it was decommissioned, and 60 years later the silos are a world-famous dive site. Local company Undersea Adventures offers experienced divers the chance to explore the now submerged labyrinth of tunnels and control rooms that could have sent the world back to the Stone Age. Do not under any circumstances attempt to explore the sprawling facility solo.

Built between 1819 and 1834, pentagon-shaped Fort Morgan guards Mobile Bay on Alabama’s Gulf Coast. The fort saw active service right up until the Second World War, and played a vital role in the Battle of Mobile Bay during the Civil War, in which a Union fleet overcame Confederate defenders to capture the bay. The fort has struggled against hurricanes – the historic structures are currently under repair – and ghostly spirits are apparently also undeterred. Visitors have reported seeing shadowy figures and hearing the voices of former soldiers in the night.

Abandoned American prisons you won't want to stay in for long

Fort Stevens in northern Oregon was built during the Civil War to guard the mouth of the Columbia River. On 21 June 1942 it became the only military installation in the contiguous United States to be shelled by an enemy during time of war since the War of 1812, when it suffered a surprise attack from a Japanese submarine. Today it is a state park and marks the northernmost stop on the beautiful Oregon Coast Trail. During the summer visitors can take an underground tour of the gun battery that served as a Second World War command centre.

Fort Wolters began its life as a Texas National Guard training camp before being officially turned over to the US Army in March 1941. It became an enormous US Army training facility during the Second World War – its troop capacity peaked at nearly 25,000 – and during the Vietnam War it trained helicopter pilots. After being deactivated in 1975, parts of the base were turned into an industrial park. And in 1998 a small part of the former base was turned into the Fort Wolters Historical Park.

Saint Helena Island is perhaps best known as a major centre of African-American Gullah culture. But visitors digging a little deeper may stumble upon the remains of Fort Fremont, abandoned and draped in Spanish moss, and one of only two coastal fortifications to have survived intact from the Spanish-American War. Once a sprawling complex with a barracks, mess hall, hospital and stables, now only the mouldy bastions and a few shadowy tunnels remain.

Incredible abandoned islands the world forgot

Construction began on Fort Gorges in 1858 in order to protect Portland harbour. But by the time it was finished in 1864 it was already obsolete, as the cannon holds were too small for modern guns. It was briefly brought back into service during the Second World War as a storage space for submarine mines, but has since been abandoned and left to decay. Today it sits despondently in the Atlantic Ocean's Casco Bay, sprouting greenery from its ramparts and accessible only by boat.

Now discover the intriguing abandoned places you can visit in every US state