From a story on axios.com by Rebecca Falconer and Sri Ravipati headlined “What to know about Titanic tourist vessel that vanished in North Atlantic”:

A tourist submersible has gone missing while on a diving trip to the wreck of the Titanic, sparking a massive search and rescue operation in the North Atlantic that entered a third day Tuesday.

What we’re watching: The U.S. Coast Guard said at a Tuesday news conference afternoon that the vessel carrying five people had an estimated 40 hours of air left from the sub’s capacity to hold up to 96 hours of oxygen.