MH370: UK submarine joins search for missing plane
British submarine HMS Tireless has joined the hunt for missing Malaysia Airlines flight MH370.
The Ministry of Defence said the Trafalgar class submarine had arrived in the southern Indian Ocean and would help search for the plane's black box recorder.
It will soon be joined by Royal Navy coastal survey ship HMS Echo.
The aircraft disappeared with 239 people on board on 8 March while en route from Kuala Lumpur to Beijing.
Earlier on Tuesday, Air Chief Marshal Angus Houston - the man co-ordinating the search from Australia - said the hunt was the "most challenging" ever seen and could take weeks.
Several floating objects have been found in recent days, but none is believed to belong to the missing plane.
Search for debris
Nuclear-powered submarine HMS Tireless was launched on 17 March 1984 and holds a crew of 130, plus 18 officers.
An MoD source told the BBC the vessel had "advanced underwater search capabilities, but the task in hand remains a tall order and the search area immense".
"Her deployment is being co-ordinated closely with our Australian and US colleagues."
The submarine will listen for ultrasonic "pings" from the plane's black box, which continue to be broadcast for about 30 days after take-off.
The MoD source said the submarine was ordered to move from an operational tasking to the search area about a week ago and arrived on Monday.
Defence Secretary Philip Hammond informed his Malaysian counterpart of the additional British contribution during a phone call on Tuesday evening.
HMS Echo is expected to begin its work on Wednesday, and the MoD said it would "play an important role in the search for debris on the sea's surface and her advanced environmental assessment capability will help to optimise search operations".
Four RAF personnel on secondment to the Royal Australian Air Force and Royal New Zealand Air Force are also actively involved in the search.
Meanwhile the personal jet of Oscar-winning film director Peter Jackson has been reported by Radio New Zealand to have joined the search for the missing Malaysian airliner.
Radio New Zealand said that Sir Peter, the director of the Lord of the Rings and The Hobbit movies, personally approved the use of his Gulfstream G650 in the search.
On Monday, Malaysian acting Transport Minister Hishammuddin Hussein said the search area was 254,000 sq km (98,000 sq miles), according to the Australian authorities.
Malaysian authorities have released the full transcript of communications between flight MH370 and Kuala Lumpur's air traffic control.
They said there was no indication of anything abnormal in the transcript, although the last words received by ground controllers are different from those previously stated.
They were "good night Malaysian three seven zero", but authorities had previously said that they were "all right, good night".
It is not clear why the account has changed.
Officials say that based on satellite data they have concluded that flight MH370 crashed into the southern Indian Ocean, but many relatives of those on board have demanded proof and expressed anger at what they perceive as a lack of information.
Various theories about what went wrong have been suggested - including the captain hijacking his own plane.
The speculation was fuelled by reports that files had been deleted on the pilot's home flight simulator.
However, on Saturday Mr Hussein said investigators had found "nothing sinister" from the simulator.