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The Soviet's Elaborate Saturation Diver Submarine In The Black Sea
The Soviet Navy Project 1840 LIMA Class submarine, was a unique special purpose boat operational in the Black Sea from 1979 until 1994. Her retro lines, reminiscent of a 1950s submarine, belied an unusual internal arrangement. There is a lot which is unclear about her mission and operations.
The submarine was designed by the 40th State Research Institute together with the Malakhit design bureau in Lenningrad (now St. Petersburg). She was laid down on October 26, 1977 in Leningrad, but transferred, via the network of inland waterways, to the Black Sea on completion. The submarine was of conventional appearance, with a length of 86m, beam of 9.5m, and displaced 2,000 tonnes surfaced and 2,450 tonnes submerged. Performance was modest, only 17 knots surfaced and 14 knots submerged, and endurance only 10-12 days. Moreover, she was unarmed.
Such a submarine may not sound very interesting at this point, so here is the twist. Instead of a torpedo room, her forward hull contained an elaborate set of pressurized chambers for divers to live, cut off from the crew. This allowed saturation diving where the divers are subjected to great pressures for days on end, only decompressing at the end of their mission. The diver habitat allowed the divers to live at pressures equivalent to a depth of 300 meters even if the submarine itself was surfaced. It also allowed the divers to decompress at a safe speed (too quick and you get Decompression sickness, aka the bends!), independent of what the submarine itself was doing.
The emphasis on LIMA appears to be on experimentation (the boat is often described as a laboratory) and training of saturation divers. These could operate down to a depth of 300 meters, much deeper than regular divers. Their missions would include seabed warfare, investigating wrecks or enemy acoustic arrays (i.e. SOSUS), and maintaining the USSR's own arrays. It is likely that the divers would be transferred to arctic waters to operate with GUGI's infamous fleet of 'research' (read: spy) submarines. It doesn't seem that the LIMA class boat was ever on the formal lists of GUGI assets however, so the waters are a bit murky.
The divers used a range of equipment including the SVG-200 deep sea diving suit. Originally this allowed dives of up to 200 meters, but later versions with an improved breathing system supported deep dives to 300 meters. This was the same operating depth as the submarine. For context, this is 7.5 times as deep as regular recommended maximum depth for recreational divers.
The SVG-200 diving suit allowed dives of up to 300 meters depth.
The boat was another victim of the 'peace dividend' and Russian economic woes after the collapse of the Soviet Union. She was decommissioned in 1994 and subsequently scrapped.
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