Now, let's tell you about the Titan submersible disaster, which you'll remember back in June of last year, gripped the world for several days, with everybody hoping that the five people on board would return to the surface, safe and sound. While knocking sounds were heard that were thought to be possibly coming from the Ocean Gate sub, but hopes were then dashed when Titan's wreckage was eventually found. Rory Golden was on the mothership at the surface at the time, and our science editor, Rebecca Gael Morrell has been speaking to him before he set sail on the first expedition to the wreck of the Titanic since the submersible disaster last year.

A service held at sea above the wreck of the Titanic to remember the 1,500 lives lost in the 1912 maritime disaster, but also those who died on board the Titan submersible in June last year. The sub was attempting to visit the wreck when contact was lost. Rory Golden was on the surface ship anxiously waiting.

When the sub was over due, we weren't on duty concerned because communications break down a lot in the ocean. But when the alarm was finally raised, that's when we realized that there were some serious issues.

A major search and rescue operation was launched, but a few days in, banging sounds were detected underwater, raising hope these were coming from the missing sub. It wasn't the case. Titan had imploded just hours into its dive.

We lived in false hope for four days. And The one redeeming thing that we can say is that at least we know they didn't suffer because we had this image in our heads of them being down there, running out of oxygen in the freezing cold, getting terribly frightened and scared. That was actually quite more frightening than the fact that we didn't know that they had died instantly.

Those who perished were British explorer Hamish Harding, the British-Pakistani businessman Shazada Darwood and his son Suleiman, French diver, PH Najahale, and Stockton Rush, the CEO of Oceangate, who owned the sub. Rory was a close friend of PH Najahale.

I was one of the last to see him. He left the ship in great spirits, in great form, and he was happy out. He was going to somewhere that he wanted to be.

A plaque is being laid to honor PH. Rory had also visited the Titanic on the Titan sub.

I made a dive two years ago when I was on the Oceangate expeditions, and I'm here, as are many others. That Titan had made 15 dives to the Titanic up to that point, so it had worked.

What do you think now about going in the sub? Do you wish you hadn't, or do you-No, I don't wish that at all.

It wasn't my time. Life is precious, and I got a second chance because you never know when your time is going to come. That certainly brought that home to all of us.

When the wreckage of Titan was finally found, Rory and those waiting on the ship knew all hope was gone.

We all cried when the remains were found in the sub. A special bond has been formed between all of us, all those who were on the ship that week. That's a bond that would always be there.

Industry experts had raised many questions about the safety of the sub, and an investigation is still ongoing. It's likely to call for changes to ensure such a tragedy doesn't happen again. Rebecca Morrell, BBC News, Providence, Rhode Island.