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DOER Marine, which is based in San Francisco, is a marine technology company that was set up in 1992.

The team there has been taking a slow and steady approach to getting to the world's deepest spot.

A large donation by Eric Schmidt, the chairman of Google, has been invested in an extensive research and development programme.

And, through a process of peer review, DOER Marine is seeking input from the scientific community so that the vessel will be tailored to their needs.

It is trying to factor in elements that can help researchers, such as a robotic arm that can collect samples.

Liz Taylor, president of DOER Marine, said: "In regard to this race to the deep, our methodology is very different.

"This isn't just a flag-planting exercise, or just to say we've been there and done that - because two guys have already been there and done that.

"We want a craft that can reliably go anywhere in the ocean - be it the deepest point, or anywhere in-between."

With its vessel still at the design stage, DOER Marine says it is some years off making its first dive.