Filmmaker James Cameron has built submersibles to go to extreme depths and knows what it takes to do it right.

In the video below he explains what happened with the Titan and how soon he knew that it had imploded:

 
Cameron was not impressed with the company who built this Titan sub nor the sub itself and how it was made, saying several times in the video above that he wished he had spoken out more.

If you want to hear more from Cameron on this, I found this longer video from him on the Titan: