Two sailors were killed yesterday by an explosion on board a Royal Navy nuclear-powered submarine as she took part in an exercise deep under the Arctic ice-cap.

The accident on HMS Tireless, a Trafalgar Class hunter-killer submarine, happened about 200 miles (320km) north of Prudhoe Bay in Alaska.

One submariner was killed in the blast and the second victim died from inhaling fumes. Next of kin were told of the deaths.

Soon after the explosion, the submarine, with 110 crew members on board, surfaced through the ice so that the hatches could be opened to let out the fumes.

Navy sources said that the smoke had been contained in the area of the explosion and that there was no other damage to equipment.

One sailor was injured and airlifted to an American military hospital in Alaska, where his condition was described as not life-threatening. Any explosion on board a nuclear-powered submarine has the potential for a disaster because of the presence of a pressurised water reactor in the central part of the boat. The reactor core is protected heavily, but crew members startled by the explosion would have needed immediate reassurance that the core was functioning normally.

The explosion was in the forward section of Tireless — at least 40 metres from the nuclear reactor compartment.

Captain Mike Davies-Marks, a submarine officer at the Ministry of Defence, said that there had been no risk of damage to the nuclear reactor.

The explosion took place in a small compartment, which contained a back-up air purification system, close to the escape hatch.

It is understood that Commander Iain Breckenridge, the commanding officer, had ordered the back-up system to be checked while Tireless was engaged in a training exercise with an American submarine, USS Alexandria.

Royal Navy sources said that the explosion in the air purification compartment was unprecedented.

Captain Davies-Marks said that there was no suggestion that either the primary or secondary air purification systems had malfunctioned. “It’s the duty of every commanding officer to test all equipment, and the explosion appears to have taken place when the tertiary back-up system was being checked,” he said.

The back-up system is needed when sailors have to leave the boat through the escape hatch during an emergency or in a training exercise. They gather in the forward compartment and breathe the oxygen that is supplied by the purification system before heading up to the surface.

The system that exploded had been upgraded and installed in the submarine — and in other Trafalgar Class boats — during a major refit. Commanding officers of all other nuclear-powered submarines were ordered yesterday not to use the back-up system, which converts carbon dioxide into oxygen.

Admiral Sir James Burnell-Nugent, Commander-in-Chief Fleet, offered his sympathies to the families of the two dead sailors. “I very much regret that this incident has occurred and my thoughts go out to the family and friends of the men who have lost their lives,” he said.

“I also wish to pay tribute to the crew of Tirelessthat this incident has been dealt with and contained so professionally.”

Tireless was involved in a major scare seven years ago, while submerged off Gibraltar, when a crack was discovered in pipework in the primary coolant system that led to the nuclear reactor.

There was no danger to the health of the sailors, but the submarine remained out of operation for a year and the Ministry of Defence recalled all other nuclear-powered boats to carry out checks. The incident caused a dispute with the people of Gibraltar because the repairs were carried out in the local dockyard. It was judged to be too risky and too costly to transport the damaged submarine back to her home base in Devonport.

A full investigation was launched yesterday into the latest accident. The MoD said that the air purification system had had a 100 per cent safety record.

Navy sources said that no damage was caused to the submarine, apart from that caused by the smoke, and that she could resubmerge if necessary. No decision had been made about whether the submarine would continue with the exercise. The training had included a study of the thickness of the ice. Sources said that the two submarines were the only vessels involved in the exercise.

Tireless had been fitted recently with Tomahawk cruise missiles. The submarine, which was launched in 1985, is armed with torpedoes and does not carry nuclear weapons.

Beneath the surface

* “Underhand, underwater and damned un-English” — Admiral Sir Arthur Wilson speaking in 1900 on why the Royal Navy should not adopt submarines

* Holland I, the Royal Navy’s first submarine, was launched in 1901. She had a crew of eight, compared with modern crews of 120

* Modern submarines produce an indefinite supply of air, water and power, so can remain submerged until food runs out

* Sonar can detect “noisy” ships from 75 miles away

* Submarines can dive to depths in excess of 250 metres and travel faster than 25mph. Maximum depths and speeds are classified

* China suffered one of its worst submarine disasters when 70 crew members were killed aboard a Ming-class submarine in 2003

* The explosions in the torpedo compartment of the Russian Kursk nuclear submarine on Saturday, August 12, 2000, were so loud they were picked up by Western seismic detectors

Source: Royal Navy, MoD, Times database

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