Official : imploded , pressure vessel collapsed - Sub of colossal fools

The single window was only certified to 1300 meter deep not 4000 where they went whitout prior unmanned testing ,the list of possible failures is endless

James Cameron hows expert on subs :
“People in the community were very concerned about this sub. Top players in the submergence community even wrote letters to the company, saying what they were doing was too experimental for passengers.”