As the tapping from the Kursk grows fainter, hope rests on a tiny diving bell

With oxygen supplies on the crippled Russian submarine Kursk rapidly diminishing and the tapping noises from the sailors growing ever fainter, rescuers last night seized on a break in the weather to try and save the 116 men trapped at the bottom of the Barents Sea.

With oxygen supplies on the crippled Russian submarine Kursk rapidly diminishing and the tapping noises from the sailors growing ever fainter, rescuers last night seized on a break in the weather to try and save the 116 men trapped at the bottom of the Barents Sea.

After a first attempt to try and reconnect power and oxygen supplies failed due to atrocious weather yesterday morning, the Russian Navy was pinning its hopes on a diving bell which it began lowering to the Kursk. The intention is to bring the sailors trapped on the nuclear submarine to the surface of the freezing waters in groups of between 15 and 20.

But last nights efforts started badly when the first attempt to attach the bell to the submarine failed.

At the end of a day of high drama and no little confusion, the head of the navy, Admiral Vladimir Kuroyedov, said he hoped emergency teams could bring out the first of the officers and crew before midnight. He said the entire operation could take up to seven hours, though given the difficulties faced by rescuers that seemed an overly optimistic assessment.

The operation - which Russia has insisted on carrying out without the assistance of other countries - has been made more difficult by the fierce weather and the position of the submarine on the sea-bed.

Speaking from the navy's Northern Fleet base at Severomorsk, a naval spokesman said: "It is difficult to work. The ships are being blown off their anchors. It is difficult for the ships to hold their course.

"All the ships and the capsule should be directed at a certain angle to ensure less resistance to the current. The storms have calmed down somewhat, although waves are still high. But the current is more important."

Despite the weather and the difficulty of attaching a diving bell to the submarine because of the angle at which it is lying on the sea-bed at a depth of more than 500 feet, rescuers are aware of the need to act swiftly. A spokesman said oxygen was running out and - somewhat ominously - that tapping noises coming from the submarine were getting weaker.

"Of course, the oxygen is running low, people just need to lie or sit down," said the spokesman.

It emerged yesterday that the Kursk - the most modern of the Northern Fleet's Oskar II class nuclear submarines - was carrying several senior ranking officers. They had been on board overseeing a major training operation involving the Northern Fleet when the submarine was crippled by an accident about 90 miles away from its base at Severomorsk, 10 miles from Murmansk.

It is believed that, contrary to earlier claims by the Russians of the Kursk being involved in a collision, the submarine was actually crippled by a self-contained explosion that took place in the torpedo tubes at the vessel's bows. A report from Norway last night said the Russians now admitted that the accident took place on Saturday rather than Sunday.

It is understood that as a result of the explosion, the front compartments in the submarine flooded with water forcing the crew to seek refuge in the rear. The submarine is designed with a series of air-tight compartments which can be sealed off in such situations.

A naval spokesman said the submarine then turned off its two nuclear reactors, robbing them of the power required for its communications and air-filter equipment. Although the submarine is designed to carry up to 24 nuclear warheads, the spokesman said the submarine was not carrying any at the time.

Despite the gloomy assessment offered by many experts, the submarine's designer, Igor Baranov, told the Russian Itar-Tass news agency that the crew should be able to survive aboard the Kursk for another two days. This raised hopes that a rescue operation could be successfully carried out up until Thursday or even Friday.

Despite the assurances from the Russians that the Kursk was not carrying warheads, there remained serious concerns among environmentalists last night about the possibility of leaking radiation. Experts in Norway have called an emergency meeting to assess what measures might need to be taken.

Part of the problem is the secrecy of the Russians and their decision to try and carry out the rescue operation without assistance from other countries which may be better equipped. Severomorsk remains out of bounds to foreigners while Zapadnaya Litsa - the actual submarine base where the Kursk was based - is off limits to everyone except those Russians who work there.

The United States has admitted that two of its submarines were in the area of the incident on Saturday though insisted that they were not involved. Historically Russian and western submarines have been involved in so-called cat-and-mouse games in the Barents Sea.

Norway has also insisted that none of its submarines were involved in the incident. The Norwegian armed forces spokesman, Brigadier Kjell Grandhagen, said: "We can say with 100 per cent certainty that there was no Norwegian submarine there."