Source

The company OceanGate have constructed a DIY submersible, that's not been tested, regulated, checked, or certified.

The CEO of the company and four civilian passengers have gone on this submersible on an expedition to the Titanic wreck.

They've since lost contact with the crew. The oxygen is calculated to run out today.

It's a huge rescue operation.

There was a private tour to the titanic that ended in 5 people dead. You can read up more here: https://wiki.slipfox.xyz/wiki/Titan_(submersible)?lang=en

//Edit: This community did not fully federate and I did not see the comments, sorry!