In a video posted to Telegram in early February, two floating barriers are shown at the entrance to the natural harbor at Balaklava in Russian-held Crimea.
Pro-Ukrainian activists claim the barriers, which can close the harbor to marine drones, are the latest evidence that a long mothballed submarine base, once known as Object 825 GTS, is being returned to service.
"The [Russian] occupiers are again using an old underground submarine base, which previously functioned as a museum, for military purposes," the Crimean Tatar guerilla group Atesh recently posted to Telegram.
The group believes the anti-drone barriers indicate the submarine base is being used for military purposes since no other sensitive facilities currently exist in the bay. Balaklava harbor was demilitarized by Ukraine in 2008, then had extensive marina facilities for pleasure craft built beginning in 2016 while under Russian control.
The Balaklava submarine base was completed in 1961 when Crimea was a key Soviet naval hub.
Balaklava's unique landscape allowed Soviet planners to tunnel straight from the sea some 600 meters through a mountain bulky enough to protect people and vessels inside from a direct nuclear strike.
The secret facility contained shelter for up to nine submarines and their crews, as well as a dry dock in which vessels could be repaired, and chambers where nuclear weapons could be stored and prepared for deployment.
Secrecy around the Soviet base led to Balaklava's harbor becoming a "closed" area, in which only those with special permits were able to enter. During the Cold War, submarines slipped in and out of the underground base only under cover of darkness.
After the breakup of the Soviet Union the base came under Ukrainian control but was left unguarded. A visitor in 1994 recalled entering the once secret site that appeared as if "it had been abandoned as a result of some sudden catastrophe," adding that "Chernobyl involuntarily comes to mind."
Much of the interior was stripped by thieves through the 1990s before Ukraine reopened the facility as a museum in 2003.
After the annexation of the Crimean peninsula by Russia in 2014, the base came under Russian control but continued operation as a museum.
Recent reports that the base is being returned to military use is only the latest such claim. In October 2022, the Ukrainian army pointed to apparent construction taking place near an entrance to the submarine base as evidence it was being returned to military duties. The museum, however, appears to remain open to the public.
John C. K. Daly, a defense expert for The Jamestown Foundation told RFE/RL if the facility is currently being used by the Russian Navy it would be for ships, rather than submarines. "Given size constraints of the Black Sea Fleet's Kilo-class submarines (their beam is too broad for Balaklava's current configuration), its use at present before renovation would necessarily be for surface ships."
With Russian naval ports being targeted by Ukraine's rapidly evolving marine drones, it is possible Russian naval ships are being sheltered in sections of the base, including vessels previously berthed at the nearby Sevastopol Naval Base, which has repeatedly been hit by Ukrainian sea drones and missiles.
Daly says the rapidly evolving marine drone technology being deployed by Ukraine has been "one of the most unexpected and significant developments" of the Russian invasion.
