It is the Coast Guard of the American city of Boston that has informed the BBC that a search operation is underway to locate the submarine.
It is not clear how many people were on board when the submarine went missing. The small submersibles are occasionally used to transport groups of tourists to the bottom of the Atlantic Ocean to view the wreck of the Titanic. The famous shipwreck lies at a depth of 3,800 meters, about 600 kilometers off the coast of Newfoundland in Canada.