It is going to prove very difficult to rescue the tourist submersible ‘Titan’, missing since it began its dive to explore the Titanic wreck on Sunday with 5 people on board.

Notably, the fact that communication with the vessel has been lost means that rescuers are not even sure if it is currently on the ocean floor (about 3,800m down) or on the surface, although it is unlikely to be stuck anywhere between these two limits. If it is on the ocean floor then it is in absolute darkness and experiencing incredible pressure (every 10m depth of water adds another atmosphere of pressure) and there are significant currents in the water which can move the craft. It has been speculated that the sub might have become entangled with the wreck of the Titanic itself which could hamper a rescue even if it can be located. If it is on the surface, the occupants are still in peril as they are effectively locked in from the outside and therefore dependant on the submersible’s air supply – which started as a 96-hour capacity.

Efforts at this stage are focused on trying to locate the vessel by listening for noises generated by the trapped crew, detected using sonar buoys – with a number of these having been deployed by rescue aircraft. If the noises can be picked up by more buoys it will help to narrow the search area considerably but the operation has been realistically compared to looking for a needle in a haystack.