GEOFF BENNETT: As we reported, search crews are looking for a submersible craft that was taking tourists to see the Titanic and ultimately went missing.

For more on this effort, we turned to Kristin Romey, an editor for National Geographic.

Thank you for being with us.

And as we learn more, Kristin, about this search-and-rescue effort, help us understand first the difference between a submersible and a submarine and what these vessels are typically used for.

KRISTIN ROMEY, National Geographic: Right.

A submersible can't power by itself, unlike a submarine, which could leave port, steam out to where it needs to go and come back.

A submersible is reliant upon a mother ship.

And, currently, that mother ship is some 900 miles, nautical miles east of Cape Cod.

GEOFF BENNETT: As we understand it, rescuers are looking about 900 miles, as you said, off the coast of Cape Cod, about 13,000 feet deep.

They're searching through the water.

How difficult, onerous a process is this?

KRISTIN ROMEY: Well, when you consider that it's very -- it's almost more difficult to travel to the bottom of the ocean than it is to space nowadays, I mean, everything down there is conspiring to keep humans out.

When you think about it, 12,500 feet, which is where the Titanic is roughly, you're talking about 380 times the pressure that's being expended on you versus at sea level.

On top of that, I mean, you have extremely cold temperatures.

It's an inhospitable place.

And you're trying to find a submersible the size of a truck at the bottom of the vast expanse of the North Atlantic.

GEOFF BENNETT: What is known about the company that owns the submersible that's now missing?

KRISTIN ROMEY: OceanGate has really been a leader in developing these deep sea submersibles.

I spoke to the CEO, Stockton Rush, when he was actually developing this submarine back in 2016.

The Titan is very unique, in that it is a carbon fiber and titanium submarine.

Up until now, most of the tourist rides to Titanic have been on very older Soviet steel submersibles.

So this is new technology.

And it does come with a real-time monitoring system that monitors the integrity of the hull.

So it's interesting that we haven't been hearing anything regarding that, because, if there was an issue with the hull, we would think that there would be some information being conveyed to the mother ship.

GEOFF BENNETT: Help us understand the increase in the numbers of people who have been going on these extreme, dangerous excursions post-pandemic.

KRISTIN ROMEY: Well, I mean, it began before the pandemic, but it's a combination of technology and people who have the money to kind of create - - create these bucket lists and achieve them.

I mean, what Stockton Rush is doing with OceanGate is very closely paralleling what we're seeing in the commercial space field, particularly with Blue Origin, as well as Virgin Galactic.

So, this is a new emerging brave new world of travel.

And it does not come without risk.

GEOFF BENNETT: And, Kristin, understanding that you're learning more about this case at the same time we are, what more is known about the five people who were on board this craft?

Have we heard from their families?

KRISTIN ROMEY: Well, right now, there are no discussions regarding who is on board.

There has been a little bit in social media.

I think that the concern really, before we identify who is on there, is just getting them up.

There is a limited amount of oxygen on this submersible, roughly 96 hours, four days' worth of oxygen.

If this submersible did indeed leave around 2:00 a.m. Sunday morning East Coast time, as they estimate, they're about halfway through that available oxygen supply.

GEOFF BENNETT: And what will you will be watching for as this search-and-rescue effort continues?

KRISTIN ROMEY: It is a massive deployment of resources, Canadian Navy, Canadian Coast Guard, U.S. Coast Guard.

This is an amphibious rescue mission.

There are -- we have ships patrolling with sonar.

We have airplanes actually flying over the North Atlantic who are able to detect objects deep below.

And we hope that they get to them in time.

GEOFF BENNETT: Kristin Romey, thanks again for being with us with that reporting and your insights.

We appreciate it.

KRISTIN ROMEY: Thank you.