Rescue teams are in a race against time after a tourist submersible carrying five people went missing during a dive into the wreck of the Titanic.
But how are rescuers trying to find a vessel that has already been missing for nearly three days in the vast depths of the Atlantic Ocean and what will the challenges be when they do?
The crew of the Titan submersible lost contact with its surface vessel – the Polar Prince – an hour and 45 minutes after it began a dive to see the wreck on Sunday. The sub’s air supply is expected to run out at about 11:00 BST (10:00 GMT) on Thursday.
The Titanic wreck lies some 435 miles (700km) south of St John’s, Newfoundland, and about a dozen ships are at the scene or on the way to help the rescue mission but changeable weather and poor visibility are hampering efforts.
Prof Alistair Greig, a submarine expert from University College London, says one of the big problems is that rescuers do not know whether to look on the surface or the seabed – it is “very unlikely” to be in between – and warns searching each poses challenges.
If the sub can’t send distress signals for any reason, Prof Greig says: “It’s about the size of a large transit van and it’s painted white so trying to see that from the air… is going to be a real challenge.”
US and Canadian agencies, navies, and commercial deep-sea firms are all helping the rescue operation, which is being run from Boston, Massachusetts.
The Polar Prince has been joined by seven ships to search an area of more than 25,000 sq km with the aid of military planes and sonar buoys.
Some of those ships are carrying unmanned remotely operated vehicles (ROVs) that will be needed to scour the sea floor.
Polar Prince (on site) – A research vessel that launched the Titan submersible
Deep Energy (on site) – Commercial cable-laying ship with two ROVs that can operate down to 3,000m (10,000ft)
Atlantic Merlin (on site) – Canadian offshore supply vessel with a 4,000m winch system. Carries ROVs but it’s unknown how deep they can operate
Skandi Vinland (on site) – Subsea support vessel with two ROVs but it’s unknown how deep they can operate
L’Atalante (on site) – French-operated ship heading to the scene with an ROV that can operate at depths of Titanic wreckage
Horizon Arctic (on site) – Commercial vessel loaded with support equipment
Glace Bay (in the vicinity on standby) – Canadian naval ship carrying decompression chamber and ready to provide medical assistance
John Cabot (on site) – Scientific research vessel with sonar search capabilities operated by the Canadian Coast Guard
Ann Harvey (on site) – Light icebreaker vessel operated by the Canadian Coast Guard
Terry Fox (en route) – Heavy icebreaker vessel operated by the Canadian Coast Guard
Source- BBC
