In the temporarily occupied Crimea, in Balaklava, there is a mysterious underground submarine base, known as Object 825, which periodically attracts attention for various reasons.
First, russian occupiers created a Cold War Museum on this base, where the exhibit is the S-49 diesel-electric submarine of Project 633, which once belonged to the russian Black Sea Fleet. Secondly, reports occasionally emerge suggesting that russians are conducting military activities at Object 825.
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The primary source in this case was a report from the Atesh partisan movement, which stated that russians in Balaklava Bay were reinforcing engineering barriers in preparation for a potential attack by Ukrainian maritime drones and possible sabotage groups.
In addition, this report states that "the occupiers are repurposing the old underground submarine base, which once functioned as a museum, for military purposes. The facility, known as Object 825 GTS, is located in Balaclava and is an underground complex capable of sheltering submarines and providing repair and maintenance".
The wording is somewhat ambiguous, and at first glance, it might suggest that russians are preparing to reopen the complex to deploy their Project 636.6 submarines armed with Kalibr cruise missiles, similar to how Object 825 was used during the Cold War.

However, it would not be entirely accurate to claim that russians have used Object 825 in Balaklava exclusively for civilian purposes up to this point. For example, it is known that in 2022, Balaklava Bay was used as a berth for the patrol ships of the Federal Security Service of the russian federation’s Coast Guard, which are also part of the overall defense system of russian occupiers in Crimea.
In this case, the Russians always have reason to worry about the reliability of Balaklava Bay's defense system. However, the concern does not lie in the type of ships or vessels that could be deployed there, but rather in the fact that the facility is under the supervision of the Federal Security Service.
Moreover, in the fall of 2022, there were also reports of the unclear nature of russian activity in Balaklava Bay. As we can now understand, the focus was more on modernizing the berthing infrastructure for surface patrol ships, although at the time, it appeared that the russians genuinely intended to resume the operation of the base for their submarines
However, here we are referring to an underground base, which main structures were carved into the rock and designed for submarines much smaller than the ones russians now have at their disposal.

As we can see in the photo, the S-49 museum submarine fits perfectly into the dimensions of the Object 825 base structures. However, it should be noted that the S-49 has a hull length of 76.7 meters, a width of 6.7 meters, and an average draft of 5 meters.
In turn, the Kalibr missile carriers of the Project 636.6 Varshavyanka-class submarines have a hull length of 73.8 meters, a width of 9.9 meters, and an average draft of 6.2 meters. That is, there is a risk that the Varshavyanka may simply not fit into the dimensions of the Object 825 base structures without additional work in the rocky part of the facility.
Against this backdrop, it seems more likely and practical for russians to keep their Kalibr carriers at a remote base in Novorossiysk, where no additional infrastructure work is required.

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