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Chinese submarine appears to be using underground base in …
Underwater tunnel - Wikipedia
Inside Yugoslavia's Secret Naval Tunnels - Radio Free …
9 of the longest underwater tunnels in the world - Interesting …
Chinese Navy Submarines Are Protected By Underground Tunnels - Forbes
Submarine Tunnel - Speed Boat Kotor Montenegro
China’s longest underwater highway tunnel opens | CNN
Covert Shores - H I Sutton
Satellite images reveal Chinese expansion of submarine base - Defense News
Submarine Tunnels - Speedboat Kotor