A serious challenge ... in the technological and moral and psychological sense

Admiral Vladimir Kuroyedov

Visibility inside the ship will be very poor - almost zero - and it will be bitterly cold.

Divers will have to be very careful not to puncture their bulky pressure suits on jagged metal, or rip their air hoses. One tear could be fatal.

But first the divers need to actually get into the Kursk. Stormy weather has hampered relief efforts and it is proving difficult to drill into the submarine.

Stormy weather

The 18-strong team of Russian, British and Norwegian divers are using under-water blow-torches to cut two holes through the Kursk's tough double-steel hulls 108m (355ft) below the surface, in cold Arctic waters.

The operation is being run from the Regalia

The 100 sq metre Regalia diving platform, from where the operation is taking place, is built to withstand winds of up to gale force five and uses satellite navigation and thrusters to remain in position above the divers.

But very high waves can heave the platform ship up and down, jeopardising the safety of divers underneath. The operation had to be delayed on Monday when waves up to 9m high put the divers at risk.

The divers are drilling holes in precise locations that have been tested on the hull of Oscar-II class submarine, the Orel.

The plan was set up in the Rubin design bureau in St Petersburg, Russia. Each hole was projected inside the submarine to check the width of the wall panels, the position of oil pipeline work, ballast tanks and other obstacles.

But no-one knows exactly how the two explosions inside the Kursk may have changed the layout of the ship.

Entering the sub

The divers have managed to cut a hole into the eighth compartment, at the rear of the ship, where there appears to be the least damage.

But they will need to cut an entrance wide enough to comfortably allow them into the Kursk to retrieve the bodies.

The hole, 1.5m by 75cm (around 5ft by 2ft) will have to be cut through two layers - the 40mm thick outer shell and then the 200mm inner shell.

Each layer of steel is separated by 8in rubber to muffle mechanical sounds and make the submarine inaudible to enemy sonar.

Work has also begun to set up equipment to cut through the outer hull leading to the seventh compartment.

It will take at least 15 hours to cut the two holes and in all, the divers must pierce seven holes to reach all parts of the submarine where remains of crew members might be found.

The divers have been working in teams - two Russians and one foreign diver - and rest between dives in a pressurised chamber inside the Regalia, to prevent injury to their lungs and other organs.

They breathe a helium mixture, which affects the vocal chords and makes their voices shrill.

When the first hole is made, one Russian diver will go inside, with a torch, video equipment and a 20m long cable.

Another diver will back him up, while a Norwegian diver will stay in a diving bell 5m from the submarine.

Painstaking task

Recovered bodies and body parts will be packed into plastic containers and taken to the surface by rope.

Adding to the high risk and physical rigour of the divers' work is the psychological pressure of working with the dead, the ever-present possibility they will collide face to face with a floating corpse.

Russian navy commander, Admiral Vladimir Kuroyedov described the rescue effort as a "serious challenge ... in the technological and moral and psychological sense".

Even if remains are successfully taken out of the submarine, raising them to the surface will be hard, requiring a slow, gradual decrease in pressure.

If raised quickly, the bodies would be torn apart by the high pressure inside them.

Visibility problems

Last month a team of scientists from the Murmansk Marine Biological Research Centre visited the area of the accident and found no trace of radiation near the ship.

That is one less danger for the divers to worry about, but despite the complex operation, expected to cost about $7m, experts warn that at best the divers will only be able to recover about 40 bodies.

Aware of the risks, marine experts and even many of the victims' families now say the bodies should be left inside the submarine until it is brought to the surface.

And Russian Navy officials have said they may cancel the effort if experts decide the operation is too dangerous for the divers.