Details of possible cause.
Submarine blast 'caused by oxygen candle'
By Tim Hall
Last Updated: 8:53am GMT 22/03/2007
An investigation is underway today into an explosion aboard a nuclear submarine which left two Britons dead.
Early reports suggest yesterday's accident aboard HMS Tireless was caused by the explosion of an emergency air-purification device, known as an oxygen generation candle.
The device is fitted to all Trafalgar-class submarines, and the MoD has ordered crews not to use it until the investigation is complete.
Experts said that the piece of equipment is not vital to the operation of the vessels and the submarines will not need to return to base.
The HMS Tireless, which has a standard crew of 130, was taking part in a joint Anglo-American operation beneath the Arctic icecap.
The submarine was forced to surface through the polar ice after the explosion damaged a forward compartment.
The MoD confirmed that two submariners had been killed and a third had been airlifted to a hospital at Elmendorf Air Force Base in Anchorage. He is expected to make a full recovery.
The HMS Tireless is powered by nuclear fuel but does not carry nuclear weapons. The MoD said that there was no danger of a nuclear explosion.
A spokesman said: "The submarine, HMS Tireless, was never in any danger, its nuclear reactor was unaffected, it quickly surfaced and is completely safe.
"Tireless is a hunter-killer submarine and does not carry nuclear missiles."
Admiral Sir James Burnell-Nugent today paid tribute to the men killed. He said: "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.
"I also wish to pay tribute to the crew of HMS Tireless that this incident has been dealt with and contained so professionally."
Vice Admiral Jay Donnelly, commander of the US Submarine Force, added: "I am deeply saddened at the loss of the crew members from the Tireless.
"Submariners are brothers at sea and we all feel the loss as if it were our own. We stand by to continue to assist in any way we can."
Tireless, based in Devonport, Plymouth, which was launched in 1985, has encountered a series of problems in recent years.
In 2000 it suffered a leak in pipe work leading from the nuclear reactor system and had to spend a year in a Gibraltar dockyard. The problem, initially said to be minor, was later acknowledged to be more serious and 12 Royal Navy subs of the same class were recalled for checks. They were later given the all clear.
Three years later a ballast tank aboard the Tireless was damaged during a collision with an object while submerged.
In 2004 the submarine was prevented from operating at sea for more than a year because of a "theoretical safety concern" which led to further checks of the nuclear reactor.