The Soviets tunneled into the mountain to conceal themselves: Submarines were entering the base from beneath the sea.

Among the projects developed to safeguard military secrets during the Cold War, the Balaklava Submarine Base stands out for its unconventional architecture.

The primary purpose of the facility, built by the Soviet Union under the code name "Object 825 GTS," was to protect submarines in the Black Sea from potential attacks and keep military operations out of the enemy's sight.

Thanks to the complex embedded within the mountain, submarines could reach the underground channels directly from the open sea.

120,000 Tons of Rock Were Removed From the Mountain.

Construction of the base began in 1953 and was completed in 1961. During construction, roughly 120,000 tons of rock were extracted from the mountain to create a vast underground complex.

At the center of the facility, a 602‑meter‑long water channel was designed to accommodate seven submarines simultaneously.

The underwater connections that allowed submarines to enter the base without surfacing were one of the facility's most important secrecy elements.

Special Protection Against Nuclear Attack Provided

The facility in Balaklava was planned not only as a covert shelter but also as a military center capable of continuing operations in the event of a nuclear war.

Heavy steel doors and reinforced concrete structures installed at the complex's entrances were designed to withstand the shock wave that a 100-kiloton nuclear blast could generate.

Inside, independent air filtration systems, power units, and food storage facilities for long-term use were also established.

This equipment was intended to allow personnel to continue living independently from the outside world under the radioactive fallout conditions that could arise after a nuclear attack.

Submarines were undergoing maintenance and munitions operations.

The underground complex's function was not limited to storing submarines. Maintenance and repair work on military vehicles was also carried out at the facility.

While torpedo and nuclear munitions were being loaded in the special sections, the mountain's thick rock layer made it difficult to detect these activities from the air.

Thus Balaklava became one of the Soviet Navy's strategic points in the Black Sea.

Military activities ended in 1993.

The submarine base, which began to lose its importance after the collapse of the Soviet Union, was closed in 1993.

With the end of military use, some parts of the complex were converted into a museum. Once the building was one of the world's most secret military facilities, it is now open to visitors.

The long underground tunnels, submarine channels, and protected military areas showcase the extraordinary engineering projects of the Cold War era.