'Giant' mission to raise the Kursk

By CNN's Tammy Oaks

MOSCOW, Russia -- The operation to attempt to lift the sunken Kursk submarine will be a highly-complex mission.

A special pontoon, dubbed "the Giant," capable of lifting massive weights will be used after an earlier attempt to lift the vessel failed.

The Russian nuclear submarine sank on August 12 last year with 118 crew on board after a series of powerful explosions, which Russian officials said were caused by the vessel's torpedoes.

Now a team of international experts have been contracted to raise the submarine, and the Norwegian ship Mayo carrying Russian and Norwegian divers, international experts and equipment arrived in the Barents Sea on July 15.

RESOURCES Animation: How the Kursk will be raised   (Web link courtesy of kursksalvage.com  -- External sites are not endorsed by CNN Interactive)    IN-DEPTH Raising of the Kursk   • Russia's military plight   • Kursk namesake   • Comparative sizes   • Diagram: Last refuge   • Damage to the sub   • Timeline of sinking   • News search   • Message board   • Quick vote   • In-depth: Sub disaster   • Download salvage images     From kursksalvage.com   • Kursk salvage animation     From parallelgraphics.com     (External sites not endorsed by CNN)

The Russian government has contracted the Dutch salvage company Mammoet and the Rotterdam-based marine services firm Smit International to attempt to recover the Kursk.

The companies' joint web site says the special pontoon is 140 metres long and 36 metres wide (460 by 120 feet) -- bigger than five tennis courts.

The pontoon, which has been fitted with 26 strand jacks -- special lifting cables -- and is capable of lifting up to 23,000 tonnes, will be used to hoist the submarine from the sea bed.

According to the web site, divers working in temperatures between 0 and 6 degrees Celsius will cut holes in the Kursk's hull using water jets by means of high-pressure water and abrasives.

The Kursk's bow -- where the torpedoes were stored -- will be cut free and left on the seabed so that the rest of the vessel can later be lifted as a compact load.

The lifting cables will be lowered from the pontoon and anchored in the holes in the Kursk using large steel plugs.

When the weather permits, the submarine will be raised to just below the pontoon. Once it has been raised, the Kursk will be towed to Murmansk. On arrival, the Giant/Kursk combination will be lifted by auxiliary pontoons in order to sail it into a dry dock.

Russian and Norwegian divers retrieved 12 bodies from the Kursk in November but their mission was called off because of rough weather and the danger from broken equipment inside the submarine.

Officials found a note in the pocket of one of the recovered submariners saying that 23 sailors had remained trapped alive in the ninth compartment for several hours after the Kursk sank.

Eighteen divers -- half from the Russian military and half from a Norwegian company -- worked around the clock in teams of three on the operation.

The team cut a hole, 1.5 metres by 75cm (5ft by 2ft), through the 40cm (16-inch) hull after five days of work and pumped water into the submarine under high pressure to eliminate silt and debris that might have made the recovery process more difficult.

Remote-controlled cameras were also lowered inside the submarine to measure radiation levels in case of any nuclear leaks.

Officials say the Kursk did not carry nuclear weapons and its nuclear reactors were shut down to avoid radiation leaks.

The Kursk is lying at a depth of more than 100 metres (330 feet). The salvage is expected to be completed in September.

The Mayo, a high-tech diving support ship which has seen regular service in the North Sea oil industry, is owned by the Norwegian-Scottish company DSND Subsea, based in Aberdeen.