"We were his big secret project this was to make a record dive to bottom of the planet," says Graham Hawkes, from Hawkes Ocean Technologies.
The Deep Space Challenger looks like a plane, but is actually a winged submersible - capable of diving to the lowest spot on Earth, The Mariana Trench. It is 37,000 feet below the surface and until now, the ship has been kept under wraps in a Richmond warehouse.
"It would have dramatically, dramatically opened the oceans for exploration. It would have been a game changer," said Hawkes.
Hawkes says the craft would have "flown" to the bottom of the ocean in an hour and 40 minutes and then rocketed back up. He wouldn't say what it cost to build, but it was almost ready to launch when Fossett disappeared.
"We finished testing all of the systems have been tested under pressure at the Department of Defense facilities. We were four weeks away from splashing it in," said Hawkes.
But now that Fossett has died, the project is on hold.
"Deep Flight Challenger is, I think, in my eyes, an extraordinary beautiful machine in my eyes, not like any else seen on this planet before," said Hawkes.
Hawkes owns the design, but the craft itself is owned by the Fossett estate, which has not yet decided what to do with it.