Stockton Rush, the CEO of OceanGate who was killed on board the Titan submersible, repeatedly dismissed warnings over the safety of the sub, emails between Rush and a deep sea exploration expert seen by the BBC show.

In messages seen by the BBC, Rush described criticism of Titan’s safety measures as “baseless lies” from “industry players” who were trying to stop “new entrants from entering their small existing market.”

The emails between Rush and Rob McCallum, a leading deep sea exploration specialist, ended after OceanGate’s lawyers threatened legal action, McCallum said. In one email McCallum writes to Rush "I think you are potentially placing yourself and your clients in a dangerous dynamic. In your race to the Titanic you are mirroring that famous catch cry: ‘She is unsinkable’."

He told the BBC that he repeatedly urged OceanGate to seek certification for the Titan before using it for tours. The vessel was not registered with international agencies, nor was it classified by a maritime industry group tasked with setting basic engineering standards.

McCallum was among more than three dozen industry leaders in the submersible vessel field who signed a 2018 letter warning Rush of possible “catastrophic” problems with Titan’s development.

In one email, McCallum writes to Rush: "I implore you to take every care in your testing and sea trials and to be very, very conservative."

Rush, however, expressed frustration, writing in one email: "We have heard the baseless cries of ‘you are going to kill someone’ way too often. I take this as a serious personal insult."

The OceanGate co-founder defended his company’s '“engineering focused, innovative approach” which “flies in the face of the submersible orthodoxy,” and said he himself was “well qualified to understand the risks and issues associated with subsea exploration in a new vehicle.”