Yugoslavia, during the Cold War, undertook one of Europe’s most ambitious and costly military-engineering projects: they excavated a secret air base hidden inside a mountain. It was a permanent setup similar to what the Rebel Alliance did in Star Wars by hiding its base from the Empire, but on a real, lasting scale. It is the Željava base.
Beyond concealing aircraft and pilots, it was designed to withstand the impact of an immense nuclear bomb and keep operating. The result was kilometers of tunnels surrounded by intricate facilities that the Yugoslavs, under the orders of Marshal Tito, spent more than ten years conceiving. It remained in operation for several decades, until it was partially demolished during the Yugoslav Civil War. Today, this base is no longer secret and can be visited.
The most expensive military secret of the former Yugoslavia
The Željava base, whose military designation was Objekt Klek 505, was excavated on Mount Plješevica: right at what is today the border between Croatia and Bosnia and Herzegovina. The military-political leadership of Yugoslavia decided to conceive it amid a historical period ruled by fear of a nuclear war. Its design was finalized in 1954, and its construction took place between 1956 and 1968. In total, 12 years.
The total cost remains a mystery, as it was highly secret. But it is said they spared no expense, as John Hammond might say: estimates range from $6 to $8 billion. Adjusted to present-day values, the figure would be more than €22 billion.
This ambitious investment materialized in about 3.5 km of tunnels carved into the bowels of Plješevica, interconnected and arranged in an M-shape. Under the mountain there was not only space for aircraft: there were workshops, technical and communications facilities, and all the systems needed to keep the base operational, in addition to space to house hundreds upon hundreds of soldiers.
An air-bunker base, built to survive a 20-kiloton bomb
This immense installation was conceived so that the outside world would be insignificant: the mountain itself served as a shield and the entrances were protected by enormous pressurized doors weighing around 100 tons. There were four, designed for the entry and exit of jet fighters in separate tunnels, connected to exterior runways.
The secret Željava air base was not alone: it formed part of a vast military complex spread around it, with auxiliary airfields, radar stations, and anti-aircraft positions. But the key installation lay hidden within the tunnel network, becoming a true, large-scale military bunker. Its major claim to fame: being
Objekt Klek 505 could house nearly 60 aircraft: two squadrons of fighters, including the Yugoslav Air Force’s MiG-21s, and another squadron for reconnaissance. It also had capacity for 1,000 soldiers and military personnel, with provisions to last a month. The tunnel network was complemented by an underground water supply and an electric generator, the latter fed by fuel delivered from a hidden depot located kilometers away through underground pipes.
The nuclear war never came, but the Yugoslav wars did
Željava survived the Cold War, during which no nuclear attack occurred, but not the dissolution wars of Yugoslavia. In October 1991, Croatian pilot Rudolf Perešin defected, escaping in a MiG-21 fighter. Soon after, another Croatian pilot, Daniel Borović, did the same. The breakup of Yugoslavia left it in disputed territory between Croats and Serbian forces, so the Yugoslav People’s Army (JNA) chose to destroy the base to prevent its use by rivals.
Thus, in 1992, during the JNA withdrawal, the exterior runways were destroyed. Then the underground complex beneath the mountain was blown up with several tons of explosives. The tunnels were burnt, some partially destroyed, and the passage of time and looting did the rest.
Today, this secret base has become a common destination for extreme tourism, much like Chernobyl. It is advisable to do it with a guide, since the surroundings are mined and the installation has compromised or contaminated areas. On the official website, visits can be booked, with a tour lasting about two hours, including the tunnel recorrido, several underground zones, and a Douglas C-47. Still, some venture to do it on their own, often YouTubers: thanks to their videos we can see these installations born to endure a nuclear war that never happened.
Images | Wikimedia, Krunchi on flickr
